Drug

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I INTRODUCTION

Drug, substance that affects the function of living cells, used in medicine to diagnose, cure, prevent the occurrence of diseases and disorders, and prolong the life of patients with incurable conditions.

The availability of new and more effective drugs, such as antibiotics, which fight bacterial infections, and vaccines, which prevent diseases caused by bacteria and viruses, helped increase the average American’s life span from about 60 years in 1900 to about 78 years in 2005. Drugs have vastly improved the quality of life. During the 20th century, drugs enabled the eradication of smallpox, once a widespread and often fatal disease. By the early 21st century, vaccines had led to the near eradication of poliomyelitis, once feared as a cause of paralysis.

II CLASSIFICATION OF DRUGS

Drugs can be classified in many ways: by the way they are dispensed——over the counter or by prescription; by the substance from which they are derived—plant, mineral, or animal; by the form they take—capsule, liquid, or gas; and by the way they are administered—by mouth, injection, inhalation, or direct application to the skin (absorption). Drugs are also classified by their names. All drugs have three names: (1) a chemical name, which describes the exact structure of the drug; (2) a generic or proprietary name, which is the official medical name, assigned in the United States by the U.S. Adopted Name Council (a group composed of pharmacists and other scientists); and (3) a brand, or trade, name, given by the particular manufacturer that sells the drug. If a company holds the patent on a drug—that is, if the company has the exclusive right to make and sell a drug—then the drug is available under one brand name only. After the patent expires, typically after 17 years in the United States, other companies can also manufacture the drug and market it under the generic name, or give it a new brand name.

Another way to categorize drugs is by the way they act against diseases or disorders: chemotherapeutic drugs attack specific organisms that cause a disease without harming the host, while pharmocodynamic drugs alter the function of bodily systems by stimulating or depressing normal cell activity in a given system. The most common way to categorize a drug is by its effect on a particular area of the body or a particular condition.

A Endocrine Drugs

Endocrine drugs correct the overproduction or underproduction of the body’s natural hormones. For example, insulin is a hormone used as a drug to treat diabetes. Another example of endocrine drugs are birth control pills, which contain the female sex hormones estrogen and progesterone.

B Drugs that Fight Infections

Anti-infective drugs are classified as antibacterials, antivirals, or antifungals depending on the type of microorganism they combat. Anti-infective drugs interfere selectively with the functioning of a microorganism while leaving the human host unharmed.

Antibacterial drugs, or antibiotics—sulfa drugs, penicillins, cephalosporins, and many others—either kill bacteria directly or prevent them from multiplying so that the body’s immune system can destroy invading bacteria. Antibacterial drugs act by interfering with some specific characteristics of bacteria. For example, they may destroy bacterial cell walls or interfere with the synthesis of bacterial proteins or deoxyribonucleic acid (DNA)—the chemical that carries the genetic material of an organism. Antibiotics often cure an infection completely. However, bacteria can spontaneously mutate, producing strains that are resistant to existing antibiotics.

Antiviral drugs interfere with the life cycle of a virus by preventing its penetration into a host cell or by blocking the synthesis of new viruses. Antiviral drugs may cure, but often only suppress, viral infections; and flare-ups of an infection can occur after symptom-free periods. With some viruses, such as human immunodeficiency virus (HIV), which causes acquired immunodeficiency syndrome (AIDS), antiviral drugs can only prolong life, not cure the disease.

Vaccines are used as antiviral drugs against diseases such like mumps, measles, smallpox, poliomyelitis, and influenza. Vaccines are made from either live, weakened viruses or killed viruses, both of which are designed to stimulate the immune system to produce antibodies, proteins that attack foreign substances. These antibodies protect the body from future infections by viruses of the same type (see Immunization).

Antifungal drugs selectively destroy fungal cells by altering cell walls. The cells’ contents leak out and the cells die. Antifungal drugs can cure, or may only suppress, a fungal infection.

C Cardiovascular Drugs

Cardiovascular drugs affect the heart and blood vessels and are divided into categories according to function. Antihypertensive drugs reduce blood pressure by dilating blood vessels and reducing the amount of blood pumped by the heart into the vascular system. Antiarrhythmic drugs normalize irregular heartbeats and prevent cardiac malfunction and arrest.

D Drugs that Affect the Blood

Antianemic drugs, such as certain vitamins or iron, enhance the formation of red blood cells. Anticoagulants like heparin reduce blood-clot formation and ensure free blood flow through major organs in the body. Thrombolytic drugs dissolve blood clots, which can block blood vessels and deprive the heart or brain of blood and oxygen, possibly leading to heart attack or stroke.

E Central Nervous System Drugs

Central nervous system drugs—that is, drugs that affect the spinal cord and the brain—are used to treat several neurological (nervous system) and psychiatric problems. For instance, antiepileptic drugs reduce the activity of overexcited brain areas and reduce or eliminate seizures.

Antipsychotic drugs are used to regulate certain brain chemicals called neurotransmitters, which do not function properly in people with psychoses, major mental disorders often characterized by extreme behaviors and hallucinations, such as in schizophrenia. Antipsychotic drugs can often significantly alleviate hallucinations and other abnormal behaviors.

Antidepressant drugs reduce mental depression. Antimanic drugs reduce excessive mood swings in people with bipolar disorder (also called manic-depressive illness), which is characterized by behavioral fluctuations between highs of extreme excitement and activity and lows of lethargy and depression. Both types of drugs act by normalizing chemical activity in the emotional centers of the brain. Antianxiety drugs, also referred to as tranquilizers, treat anxiety by decreasing the activity in the anxiety centers of the brain.

Sedative-hypnotic drugs are used both as sedatives to reduce anxiety and as hypnotics to induce sleep. Sedative-hypnotic drugs act by reducing brain-cell activity. Stimulant drugs, on the other hand, increase neuronal (nerve cell) activity and reduce fatigue and appetite.

Analgesic drugs reduce pain and are generally categorized as narcotics and non-narcotics. Narcotic analgesics, also known as opioids, include opium and the natural opium derivatives codeine and morphine; synthetic derivatives of morphine, such as heroin (the use of which is illegal in the United States); and synthetic drugs such as meperidine and propoxyphene hydrochloride. Narcotics relieve pain by acting on specific structures, called receptors, located on the nerve cells of the spinal cord or brain. Non-narcotic analgesics such as aspirin, acetaminophen, and ibuprofen reduce pain by inhibiting the formation of nerve impulses at the site of pain. Some of these drugs can also reduce fever and inflammation.

General anesthetics, used for surgery or painful procedures, depress brain activity, causing a loss of sensation throughout the body and unconsciousness. Local anesthetics are directly applied to or injected in a specific area of the body, causing a loss of sensation without unconsciousness; they prevent nerves from transmitting impulses signaling pain (see Anesthesia).

F Anticancer Drugs

Anticancer drugs eliminate some cancers or reduce rapid growth and spread. These drugs do not affect all cancers but are specific for cancers in certain tissues or organs such as the bladder, brain, liver, or bones. Anticancer drugs interfere with specific cancer-cell components. For example, alkylating agents are cytotoxic (cell-poisoning) drugs that alter the DNA of cancer cells. Vinca alkaloids, chemicals produced by the periwinkle plant, prevent cancer cell division.

G Other Drugs

Many other categories of drugs also exist, such as anti-inflammatory, antiallergic, antiParkinson (see Parkinson Disease), antiworm (see Anthelmintic Drugs), diuretic, gastrointestinal, pulmonary, and muscle-relaxant drugs. Often a drug in one category can also be used for problems in other categories. For example, lidocaine can be used as a local anesthetic or as a cardiac drug.

III HOW DRUGS MOVE THROUGH THE BODY

The effect of a drug on the body depends on a number of processes that the drug undergoes as it moves through the body. All these processes together are known as pharmacokinetics (literally, “motion of the drug”). First in these processes is the administration of the drug after which it must be absorbed into the bloodstream. From the bloodstream, the drug is distributed throughout the body to various tissues and organs. As the drug is metabolized, or broken down and used by the body, it goes through chemical changes that produce metabolites, or altered forms of the drug, most of which have no effect on the body. Finally, the drug and its metabolites are eliminated from the body.

A Administration

Depending on the drug and its desired effect, there are a variety of administration methods. Most drugs are administered orally—that is, through the mouth. Only drugs that will not be destroyed by the digestive processes of the stomach or intestines can be given orally. Drugs can also be administered by injection into a vein (intravenously), which assures quick distribution through the bloodstream and a rapid effect; under the skin (subcutaneously) into the tissues, which results in localized action at a particular site as with local anesthetics; or into a muscle (intramuscularly), which enables rapid absorption through the many blood vessels found in muscles. An intramuscular injection may also be given as a depot preparation, in which the drug is combined with other substances so that it is slowly released into the blood.

Inhaled drugs are designed to act in the nose or lungs. General anesthetics may be given through inhalation. Some drugs are administered through drug-filled patches that stick to the skin. The drug is slowly released from the patch and enters the body through the skin. Drugs may be administered topically—that is, applied directly to the skin; or rectally—absorbed through an enema (an injection of liquid into the rectum) or a rectal suppository (a pellet of medication that melts when inserted in the rectum).

B Absorption

Absorption is the transfer of a drug from its site of administration to the bloodstream. Drugs that are inhaled or injected enter the bloodstream more quickly than drugs taken orally. Oral drugs are absorbed by the stomach or small intestine and then passed through the liver before entering the bloodstream.

C Distribution

Distribution is the transport of a drug from the bloodstream to tissue sites where it will be effective, as well as to sites where the drug may be stored, metabolized, or eliminated from the body. Once a drug reaches its intended destination, the drug molecules move from blood through cellular barriers to various tissues. These barriers include the walls of blood vessels, the walls of the intestines, the walls of the kidneys, and the special barrier between the brain and the bloodstream that acts as a filtration system to protect the brain from exposure to potentially harmful substances.

The drug molecules move from an area of high drug concentration—the bloodstream—to an area of low drug concentration—the tissues—until a balance between the two areas is reached. This process is known as diffusion. When a drug reaches its highest concentration in the tissues, the body begins to eliminate the drug and its effect on the body begins to diminish. The time it takes for the level of a drug to fall by 50 percent is known as the drug’s half-life. Depending on the drug, this measurement can vary from a few minutes to hours or even days. For example, if a drug’s highest concentration level in the blood is 1 mg/ml and this level falls to 0.5 mg/ml after five hours, the half-life of the drug is five hours. A drug’s half-life is used to determine frequency of dosage and the amount of drug administered.

Distribution of a drug may be delayed by the binding of the drug to proteins in the blood. Because the proteins are too large to pass through blood vessel walls, the drug remains in the blood for a longer period until it is eventually released from the proteins. While this process may increase the amount of time the drug is active in the body, it may decrease the amount of the drug available to the tissues.

D Metabolism and Elimination

While circulating through the body, a drug undergoes chemical changes as it is broken down in a process called metabolism, or biotransformation. Most of these changes occur in the liver, but they can take place in other tissues as well. Various enzymes oxidize (add oxygen to), reduce (remove oxygen from), or hydrolyze (add water to) the drug. These changes produce new chemicals or metabolites that may continue to be medically active in the body or may have no activity at all. A drug may be broken down into many different metabolites. Eventually, most drugs or their metabolites circulate through the kidney, where they are discharged, or eliminated, into the urine. Drugs can also be excreted in the body’s solid waste products, or evaporated through perspiration or the breath.

E Dose-Response Relationship

The extent of the body’s response to a drug depends on the amount administered, called the dose. At a low dose, no response may be apparent. A higher dose, however, may produce the desired effect. An even higher dose may produce an undesirable or harmful response. For example, to relieve a headache most adults require two tablets of aspirin. A half tablet may provide no relief from pain while ten tablets may cause burning pain in the stomach or nausea.

The doses prescribed by physicians are those recommended by each drug’s manufacturer to produce the best therapeutic, or medically beneficial, responses in the majority of patients. However, doses may need to be adjusted in certain individuals. For example, a person may be born without the enzyme required to metabolize a particular drug while other individuals may suffer from lung disorders that prevent them from absorbing inhaled drugs. Factors such as alcohol consumption, age, the method of drug administration, and whether or not the individual has taken the drug previously can affect an individual’s response to a drug.

F Receptors

Drugs interact with cell receptors, small parts of proteins that control a multitude of chemical reactions and functions in the body. Receptors have a specific, chemical structure compatible only with certain drugs or endogenous compounds—substances that originate within the body such as hormones and neurotransmitters. This relationship can be compared to that of a lock and key: A drug molecule—the “key”—attaches briefly to its specific receptor—the “lock” that only this molecule can open. The lock-and-key combination of the drug and receptor results in a cascade of chemical events. The extent of the response is determined by the number of receptors activated. Stimulation of only a few receptors may not produce a response while stimulation of a certain number of receptors is needed to produce the desired effect.

IV THERAPEUTIC RESPONSES AND ADVERSE REACTIONS

The same receptors can be found in different tissues and organs in the body, but receptors produce different responses depending on their location. As a result, a specific drug can affect the body in more than one way. Desirable effects are called therapeutic or beneficial responses. Undesirable or harmful effects are called adverse reactions. Some adverse reactions, or side effects, can be predicted. The most common side effects are drowsiness, headache, sleeplessness, nausea, and diarrhea. Other reactions, such as those that occur only in specific individuals for unexpected reasons, called idiosyncratic reactions, and those that occur with the triggering of the body’s immune system, called allergic reactions, are less predictable.

Drug toxicity, or poisoning, can occur when drugs are given in too large a dose or when individuals take a particular drug over a long period of time—the drug may build up to dangerous levels in the kidneys and liver and damage these organs. For some drugs, such as those used to treat epilepsy, the difference between therapeutic and toxic concentrations is small. Physicians constantly monitor the precise levels of such drugs in an individual’s bloodstream to prevent drug poisoning.

Other drugs, such as those used to treat cancer, are known to have toxic effects; however, the benefits outweigh the risks—that is, treatment without them may result in death.

A Drug Interactions

When taken together, drugs can interact with one another and produce desirable or undesirable results. Some drugs have an additive effect—that is, they increase the effect of other drugs. For example, alcoholic beverages intensify the drowsiness-producing effect of some sedatives. Other drugs have a reducing effect—that is, they interfere with the action of drugs already present in the body. For example, antacids prevent antibiotics from being absorbed by the stomach. Some drugs combine with other drugs to create a substance that has no medical benefit. In some cases, however, drug interactions can produce desirable results. Doctors have found that using three drugs to fight AIDS is more effective than using one drug alone.

Drugs are most effective when properly prescribed by physicians and taken correctly by patients. Missing doses, taking drugs at the wrong time of the day or with instead of before meals, and stopping drug use too soon can markedly reduce the medical benefits of many drugs.

V DRUG ABUSE

Drug abuse is characterized by taking more than the recommended dose of prescription drugs such as barbiturates without medical supervision, or using government-controlled substances such as marijuana, cocaine, heroin, or other illegal substances. Legal substances, such as alcohol and nicotine, are also abused by many people. Abuse of drugs and other substances can lead to physical and psychological dependence (see Drug Dependence).

Drug abuse can cause a wide variety of adverse physical reactions. Long-term drug use may damage the heart, liver, and brain. Drug abusers may suffer from malnutrition if they habitually forget to eat, cannot afford to buy food, or eat foods lacking the proper vitamins and minerals. Individuals who abuse injectable drugs risk contracting infections such as hepatitis and HIV from dirty needles or needles shared with other infected abusers. One of the most dangerous effects of illegal drug use is the potential for overdosing—that is, taking too large or too strong a dose for the body’s systems to handle. A drug overdose may cause an individual to lose consciousness and to breathe inadequately. Without treatment, an individual may die from a drug overdose.

Drug addiction is marked by a compulsive craving for a substance. Successful treatment methods vary and include psychological counseling, or psychotherapy, and detoxification programs—medically supervised programs that gradually wean an individual from a drug over a period of days or weeks. Detoxification and psychotherapy are often used together.

The illegal use of drugs was once considered a problem unique to residents of poor, urban neighborhoods. Today, however, people from all economic levels, in both cities and suburbs, abuse drugs. Some people use drugs to relieve stress and to forget about their problems. Genetic factors may predispose other individuals to drug addiction. Environmental factors such as peer pressure, especially in young people, and the availability of drugs, also influence people to abuse drugs.

VI HISTORY
Humans have always experimented with substances derived from minerals, plants, and animal parts to treat pain, illness, and restore health. In ancient Egypt, physicians prescribed figs, dates, and castor oil as laxatives and used tannic acid to treat burns. The early Chinese and Greek pharmacies included opium, known for its pain-relieving qualities, while Hindus used the cannabis and henbane plants as anesthetics and the root of the plant Rauwolfia serpentina, which contains reserpine, as a tranquilizer.

A school of pharmacy established in Arabia from 750 to 1258 ad discovered many substances effective against illness, such as burned sponge (which contains iodine) for the treatment of goiters—a noncancerous enlargement of the thyroid gland, visible as a swelling at the front of the neck. In Europe, the 15th century Swiss physician and chemist Philippus Aureolus Paracelsus identified the characteristics of numerous diseases such as syphilis, a chronic infectious disease usually transmitted in sexual intercourse, and used ingredients such as sulfur and mercury compounds to counter the diseases.

During the 17th and 18th centuries, physicians treated malaria, a disease transmitted by the bite of an infected mosquito, with the bark of the cinchona tree (which contains quinine). Heart failure was treated with the leaves of the foxglove plant (which contains digitalis); scurvy, a disease caused by vitamin C deficiency, was treated with citrus fruit (which contains vitamin C); and smallpox was prevented using inoculations of cells infected with a similar viral disease known as cowpox. The therapy developed for smallpox stimulated the body’s immune system, which defends against disease-causing agents, to produce cowpox- and smallpox-specific antibodies.

In the 19th century scientists continued to discover new drugs including ether, morphine, and a vaccine for rabies, an infectious, often fatal, viral disease of mammals that attacks the central nervous system and is transmitted by the bite of infected animals. These substances, however, were limited to those occurring naturally in plants, minerals, and animals. A growing understanding of chemistry soon changed the way drugs were developed. Heroin and aspirin, two of the first synthetic drugs created from other elements or compounds using chemical reactions, were produced in the late 1800s. This development, combined with the establishment of a new discipline called pharmacology, the study of drugs and their actions on the body, signaled the birth of the modern drug industry.

VII DRUG DEVELOPMENT

Today most drugs are synthesized by chemists in the laboratory. Synthetic drugs are better controlled than those occurring naturally, which ensures that each dose imparts the same effect. Some new synthetic drugs are developed by modifying the structure of existing substances. These new drugs are called analogues. For example, prednisone is an analogue of the hormone cortisone (see Hydrocortisone). Because scientists can selectively alter the drug’s structure, analogues may be more effective and cause fewer side effects than the drugs from which they were derived.

One of the newer methods for developing drugs involves the use of gene splicing, or recombinant DNA (see Genetic Engineering). In drug research, this technique joins the DNA of a specific type of human cell to the DNA of a second organism, usually a harmless bacterium, to produce a recombinant (or “recombined”) DNA. The altered organism then begins to produce the substance produced by the human cell. This substance is extracted from the bacteria and purified for use as a drug.

The first drug produced in this manner was the hormone insulin in 1982, which was created in large quantities by inserting the human insulin gene in Escherichia coli (E. coli) bacteria. This recombinant insulin has largely replaced versions of the drug extracted from pig and cattle pancreases. Since 1982 other genetically engineered drugs for humans have been developed, including tissue plasminogen activator (tPA), an enzyme used to dissolve blood clots in people who have suffered heart attacks, and erythropoetin, a hormone used to stimulate the production of red blood cells in people with severe anemia.

Because of the great expense and time involved, most new drugs are created by large, well-funded pharmaceutical companies. From idea to production, the development of a new drug can take up to ten years and cost about $200 million. The process usually starts with the idea that an existing chemical substance has therapeutic value or that the structure of an existing drug can be modified for new clinical uses. Out of 10,000 chemicals tested in a laboratory, only one may eventually become a drug.

Once drug researchers have determined that a new substance may have medical value, an elaborate testing program begins. The drug is tested first on small animals such as rats and mice, and then on larger animals such as monkeys and dogs. If these tests indicate that the new drug is effective against its intended target—such as a particular disease—and shows an acceptably low level of toxicity, the drug company requests government permission to test the drug in humans. In the United States, the Food and Drug Administration (FDA), an agency of the U.S. Department of Health and Human Services, grants or denies these requests.

If the agency approves the request, clinical trials on humans can begin. These experiments are usually divided into three phases, each of which can last from several months to several years. In the first phase, the drug is tested on a small number of healthy individuals to determine its effect on the body. The second phase tests the drug on a small number of people who have the disease or disorder the drug manufacturer hopes the drug will treat. These individuals are divided into two groups: those who receive the drug and those who receive a placebo, or inactive compound. Neither the investigating physicians nor the members of the test group know who is receiving the drug or who is receiving the placebo. This technique, called a double-blind study, ensures that no one consciously or unconsciously influence the drug’s effect. The third phase tests the drug on a much larger group of people and determines specific doses, possible interactions with other drugs, responses related to gender, and other information used for drug labeling. At the end of the third phase, a drug manufacturer compiles the results of the clinical trials and submits them to the FDA in a new product application. If the drug has been proven effective and safe, and its benefits outweigh any risks, the agency approves the drug for marketing. FDA approval of a new drug may take up to 18 months; however, the agency is working to reduce the time to 12 months for most drugs and 6 months for highly effective drugs that treat previously incurable conditions.

VIII DRUG REGULATION

Because drugs can produce harmful effects when manufactured or taken improperly, most governments control drug development as well as availability. In the United States, the FDA determines how drugs are produced and how they are sold. Drugs that can be sold over the counter (OTC)—that is, without a prescription from a physician—are called proprietary drugs. They are considered safe for unsupervised use by the general population. Drugs that must be prescribed by physicians and dispensed by pharmacists are known as ethical drugs. Their use is monitored closely by medical personnel.

The FDA regulates the sale and manufacture of drugs in the United States as outlined in applicable laws enacted over the past century. Legal standards for composition and preparation of drugs in the United States are found in the publication known as the United States Pharmacopeia (USP). Drugs that can be abused, such as the powerful narcotic heroin, are regulated by the Drug Enforcement Administration (DEA) of the U.S. Department of Justice to ensure that they are not prescribed or sold illegally.

Before 1900 any individual could sell a drug and claim it offered therapeutic benefits without medical proof. This changed after 1906 with the passage of the Pure Food and Drug Act, which required drug manufacturers to state the content, strength, and purity of each drug they produced. The Pure Food and Drug Act ended the practice of including morphine, cocaine, and heroin in drugs without the public’s knowledge. In 1914 the U.S. legislature began to strictly regulate the trade of narcotics with the enactment of the Harrison Narcotic Act; in 1937 the government added marijuana to this list of controlled substances (the Marijuana Tax Act).

The Federal Food, Drug, and Cosmetic Act was enacted in 1938 requiring that new drugs be safe for humans; however, it did not require that manufacturers prove their drugs’ effectiveness. It would be 24 years before legislation was passed that would require proof of the efficacy of new drugs (the Kefaver-Harris Amendments, 1962). Enforcement of this law was entrusted to the FDA.

Two laws enacted in the 1960s strengthened the FDA’s efforts to reduce drug abuse. The Drug Abuse Control Amendments of 1965 provided penalties for the illegal sale or possession of stimulants, sedatives, and hallucinogens, and the Narcotic Addict Rehabilitation Act of 1966 set up a federal program for addicts that provided them with the option of receiving treatment for their drug problems in place of a prison sentence.

In 1970 the Comprehensive Drug Abuse Prevention and Control Act established rules for manufacturing and prescribing habit-forming drugs. It stipulated that physicians can prescribe all drugs, but a special license is required to prescribe drugs with a high abuse potential. This license is issued by the Drug Enforcement Administration.

The Anti-Drug Abuse Acts, signed into law in 1986 and 1988, set up funding for the treatment of drug abuse and for the creation of law-enforcement programs to fight the illegal sale of drugs. These acts also detailed severe punishments for individuals selling and possessing drugs illegally. Harsh penalties for using anabolic steroids (hormones that promote the storage of protein and the growth of tissue that are sometimes abused by competitive athletes) were included in the 1988 act, along with the requirement that all alcoholic beverages be labeled with warnings about alcohol’s potentially dangerous effect on the body. The 1988 act also established the Office of National Drug Control Policy to develop an action plan that would involve the public, as well as private agencies, in eliminating the illegal sale of drugs; in helping individuals who use drugs to stop; and in preventing nonusers from ever starting to use drugs.

The U.S. government and its regulatory agencies continually monitor the development and use of all drugs sold in the United States to ensure that the American public has access only to drugs that are safe and effective. Sometimes, adverse reactions to a drug come to light after it has been approved by the FDA and used by large numbers of patients. For example, the analgesic Vioxx was approved in 1999, but in 2004 the FDA asked the drug’s maker to remove it from the market because it had been linked to heart attacks and strokes.
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Nose and Smell

Hi readers, in this article i'll to tell you something about "Nose and Smell" . hopefully useful and enrich your knowledge :) happy reading :D

Here’s a question: If you lost your nose, would you still be able to smell? Believe it or not, the answer is yes! Even though the nose is the organ of smell, it’s only the outside part. There’s an inside part that you can’t see. That’s where the smelling gets done.

THE NOSE

There are all kinds of noses in the animal world: big or small, flat or round, and long or short. In people, what we call the nose is the formation of bone, cartilage (tough tissue), and skin on the front of the face. The nose has two openings called nostrils. They allow air to come in and go out. When that happens, the nose collects the molecules of substances that cause odors.

The nose has other functions, too. The stiff hairs in the nostrils help keep out dust, dirt, and insects that you might take in when you breathe. Once inside the nose, the air you breathe is warmed and moistened in the big nasal cavity before going to the lungs. The nasal cavity is the big space behind your nostrils. It’s what gets stuffed up and swollen when you have a cold.

The size, shape, and health of your nose help determine the way your voice sounds. Pinch your nose shut and talk. Can you hear the difference?

SMELL

Smell is the detection of odors. It’s one of the five senses. The others are touch, taste, sight, and hearing.

Smelling takes place deep inside the nasal cavity. That’s because there are nerve endings called olfactory nerves located there. You actually smell stuff somewhere roughly between your eyes!

When a molecule that represents an odor hits the olfactory nerves, these nerve endings send a signal to your brain. The brain then determines what the smell is, and you recognize it. Most people can detect about 10,000 different odors! Unfortunately, one of them is dirty socks.

Smell plays a big part in the sense of taste, too. The taste buds can only detect four tastes: sweet, sour, salty, and bitter. Your sense of smell adds to these tastes. That’s why food is so rich and varied in taste. That’s also why if your nose is blocked up, your taste buds don’t work well either.

ANIMAL NOSES

For most animals, the nose and sense of smell are crucial to survival. They help animals find food. They can help animals tell friends from enemies and find mates.

Many animals have noses with extra talents. The elephant’s trunk is long like an arm and useful like a hand. It’s a trumpet when an elephant calls, and it’s a hose that allows an elephant to drink or give itself a shower.

Horses and camels can open and close their nostrils the way you can open and close your eyes. It helps them keep dirt or sand out when the wind is blowing.

A young salmon will travel thousands of miles downriver and into the ocean to live. Years later, it can use its sense of smell to return to the exact place it was born. Its ability to smell is that good! Can you imagine finding your way home from school only using your nose?
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Diseases of Animals

hi readers, in this article a'll to tell you something about "Diseases of Animals" . hopefully helpful ! happy reading :)

I INTRODUCTION

Diseases of Animals, disorders that influence an animal's health and ability to function. Animal diseases are of great concern to humans for several reasons. Diseases can reduce the productivity of animals used to produce food, such as hens and dairy cows. Animals that are raised as food, such as pigs and beef cattle, that become ill may affect the economic well-being of many industries.

Some animal diseases can be transmitted to humans, and control of these types of diseases, known as zoonoses, is vital to public health. In the wild, animal populations reduced by disease can upset the ecological balance of an area. And, in the case of pets, prevention and treatment of animal diseases helps pets live long and healthy lives, enhancing the companionship shared by a pet and its human owner.

Animal diseases are characterized as infectious and noninfectious. Infectious diseases are caused by an agent, such as bacteria or a virus, that penetrates the body's natural defense mechanisms, while noninfectious diseases are caused by factors such as diet, environment, injury, and heredity. Sometimes the cause of a disease is unknown. An animal may also experience one disease or a combination of diseases at any one time.

To identify a disease, a veterinarian (a doctor who treats animals) first determines the animal's signalment—its species, breed, age, and sex. This information helps to identify a disease because some diseases are more prevalent in certain species, or a disease may preferentially affect one sex or age group. The veterinarian then gathers a complete history of the animal and its problem. This history includes the symptoms the animal is displaying and when they first appeared, as well as whether the animal has been exposed to something new in its surroundings or to other animals. The veterinarian gives the animal a thorough physical examination, which may include measuring its body temperature, listening to its heart, checking its pulse, and feeling its abdomen and lymph nodes. The veterinarian then creates a list of possible diseases that may be making the animal sick. The list may be narrowed by running diagnostic tests such as X rays, electrocardiograms, blood analyses, and bacterial or fungal cultures. Once the disease is identified, the doctor develops a treatment plan for the animal (see Veterinary Medicine).

II INFECTIOUS DISEASES

Many microscopic organisms naturally and peacefully exist in enormous quantities within animal bodies. For example, the multichambered stomach of a cow contains bacteria that help the animal digest its food. But many other microscopic organisms, known as pathogens, cause diseases in animals. Pathogens include bacteria, viruses, fungi, prions—newly identified mutated proteins—and parasites. Pathogens are easily spread: an animal may consume food or drink something that has been contaminated with infected fecal material, for example. If the ground is contaminated by Salmonella bacteria, for instance, infection can travel from barn to barn on the soles of a farmer’s boots. Or an animal may be exposed while walking across contaminated ground. Some diseases are transmitted by biting insects; others are spread by sexual contact.

In addition to reducing the productivity of livestock, some infectious diseases pose a danger to humans. More than 100 zoonoses are recognized. Most cases are transmitted from animals that have close contact with humans, such as pets, farm animals, or rats. Examples of zoonoses include toxocariasis, a disease caused by a parasitic worm transmitted by infective eggs within canine feces; psittacosis, a respiratory disease caused by the bacteria-like Chlamydia psittaci and transmitted from infected birds; hantavirus pulmonary syndrome, spread by contact with rodent feces and urine; and rabies, a viral infection transmitted in the saliva of infected animals, typically foxes, bats, and raccoons, that causes damage to the brain and spinal cord.

As the human population grows and expands into wilderness territories, humans are coming into closer contact with other animals that carry pathogens dangerous to humans. Some of these pathogens are carried by insects, as in the case of yellow fever, spread from monkeys to humans via mosquito bites. Some hemorrhagic fevers, such as that caused by the Ebola virus, are recognized as zoonoses, but the exact transmission route from animal to human is still unknown.

A Bacterial Diseases

Salmonellosis is any disease caused by the Salmonella bacteria, characterized by septicemia and severe diarrhea. In its many forms, it is one of the major diseases of wild and domestic mammals, birds, and reptiles, as well as humans. Salmonella bacteria usually enter the body through the mouth, most commonly along with food or water contaminated by infected feces. Transmission also may occur through direct contact with an infected animal. In addition, salmonella bacteria can be spread by contact with objects, such as bowls and cutting boards, that have been contaminated by infected animal products, such as eggs or meat.

Anthrax is one of the oldest and most destructive diseases recorded in history. Caused by the bacterium Bacillus anthracis, anthrax can affect virtually all warm-blooded animals and humans. The onset of anthrax may be sudden and death may occur before symptoms are observed. In other cases, typical symptoms include restlessness, lethargy, appetite loss, fever, rapid breathing, and unsteady gait. The disease is contracted from contaminated soil, feed, or water. It can also spread when the skin is penetrated by insect bites or by objects contaminated with anthrax spores.

Leptospirosis, caused by spiral Leptospira bacteria, affects cattle, dogs, pigs, sheep, goats, and humans. Ponds, lakes, and other bodies of water are common sources of leptospirosis, and rodents may carry the infection. This infection causes kidney disease and destruction of red blood cells with potential anemia; it may also cause abortion. Brucellosis also causes abortion, as well as swelling of the reproductive organs in males. Caused by the Brucella bacterium, it occurs primarily in cattle, pigs, sheep, dogs, and goats, and may be transmitted to humans (see Undulant Fever).

Tuberculosis (TB) is a chronic disease of animals and humans, caused by bacteria of the genus Mycobacterium and transmitted by inhalation of droplets from an infected animal’s cough or sneeze, or by wound infection. TB infection causes lesions called tubercles to develop in certain tissues, such as the lung or liver. Symptoms include fever, emaciation, and progressive loss of strength.

Kennel cough is a respiratory disease of dogs that is caused by the bacterium Bordetella bronchiseptica, with or without the aid of various viruses. Symptoms include a harsh, dry cough, appetite loss, discharge from the nose or eyes, and lethargy. It typically spreads when dogs are grouped together, such as at dog shows or boarding kennels.

B Viral Diseases

Viruses are unable to grow and reproduce outside of the living cells from other hosts. Viruses attach and invade a cell and replicate, and then the newly created viruses destroy the host cell and seek out other cells to continue replication.

Feline leukemia is caused by the feline leukemia virus. Often fatal, it can seriously impair the immune system and, in some cases, cause the growth of life-threatening tumors. Spread from direct contact with an infected cat, symptoms of the disease include lethargy, weight loss, anemia, and fever. A cat may not appear ill until years after exposure.

Foot-and-mouth disease is caused by a virus found in the saliva of cattle, pigs, and other hoofed animals. Highly contagious, it is spread from direct contact with an infected animal. It may also spread in milk or in garbage that contains contaminated meat. Typical symptoms include blisters that appear on the mouth and feet; animals may become lame when their hooves degenerate.

Canine distemper is a highly contagious disease caused by the paramyxovirus, which is transmitted in discharges from the nose and eyes. Symptoms begin with fever, malaise, and nasal and ocular discharges and may progress to convulsions and other nervous system disorders. Parvoviruses affect dogs and in some cases cattle, pigs, and humans. Usually fatal if left untreated, canine parvovirus causes inflammation of the intestines, producing diarrhea, vomiting, fever, and loss of appetite.

C Fungal Diseases

A fungal infection typically develops slowly and recurs more frequently than a bacterial infection. Histoplasmosis, characterized by a chronic cough and diarrhea, is contracted by inhaling the Histoplasma capsulatum fungus, which grows in soil. In the Central United States histoplasmosis is the most widespread fungal disease diagnosed in dogs, although it also affects other animals. Ringworm, a common skin disease of many species, causes circular patches of hair loss and scaly, reddened skin. It readily spreads by direct contact with an infected animal.

Yeast, another type of fungus, grows in warm and moist places, such as the ear canals of dogs. It may cause otitis externa, an infection of the outer ear. The yeast Candida albicans is commonly found in the intestinal tract of birds and other animals. It may be the primary cause of disease, or it may be a secondary invader in an animal already sick with another infection.

D Parasitic Infections

Diseases caused by parasites are widespread in domestic animals and wildlife. Parasites may be internal or external. Internal parasites include Coccidia, a microscopic protozoal (single-celled) organism that causes diarrhea and extreme weight loss in many young animals.

Other internal parasites include the roundworm, tapeworm, and fluke. Larval roundworms can cause considerable damage to lungs and other organs in some animals. For instance, Capillaria worms may attack the lining of the digestive tract of chickens and turkeys; they parasitize the respiratory and urinary tracts of dogs. Adults of the heartworm Dirofilaria immitis, another roundworm, live in the heart of dogs and produce microscopic larval stages, which swim in the blood. Symptoms of heartworm disease include coughing, fatigue, and weight loss. If left untreated, an animal may experience heart failure. Tapeworms may have very damaging larval stages. In echinococcosis, the larval tapeworms may form large cysts in liver, lungs, and other organs of humans and animals.

Flukes may directly damage the liver, lungs, or intestines, or they may act as carriers of other disease agents, as in the case of salmon poisoning of dogs in which the fluke, encysted in the body of a salmon, carries a virulent rickettsial agent.

External parasites live or feed on the surface of the animal's body. This group includes bloodsucking insects, such as mosquitoes, gnats, some flies, fleas, and some lice. Some insects are bloodsuckers in larval stages, such as ear maggots of hawk nestlings. Others, including some larval flies and some lice, eat tissue. Great damage to the meat and hides of cattle is caused by larval flies such as the ox warble, which migrates through the tissues and, after boring breathing holes through the skin, leaves the body to reproduce. Bloodsucking flies can transmit parasitic blood protozoans and some viruses.

Lice are of two types, those with chewing mouthparts and those with sucking mouthparts. Lice cause irritation, carry disease agents, and may cause anemia. Fleas are all bloodsuckers, and may transmit larval tapeworms, roundworms, and other disease agents. The sticktight flea may kill young birds by excessive bloodsucking. Mites may be external bloodsuckers, such as the red mite of birds (it can also affect humans and other animals), or they may be internal parasites, such as the Sternostoma mites of the lungs and air passages of canaries and other birds. Ticks, larger than mites, feed on blood and can carry serious infectious agents such as the bacteria that cause Q Fever and Lyme disease, which can be transmitted to humans.

E Prion Diseases

Newly identified protein particles called prions have been found in the brains of animals that have died from diseases such as scrapie and bovine spongiform encephalopathy, more commonly known as mad cow disease. How prions act is unclear, but scientists theorize that prions attach to normal proteins in the brain. Once attached, the prions cause the normal proteins to change into an abnormal shape, leading to progressive destruction of brain cells and death. Prion diseases are thought to spread by means of feed supplements derived from infected animals. In recent years, public health officials have been concerned about the possibility that prion diseases may be transmitted to humans. This happens when humans eat contaminated beef or organs, causing them to contract such rare neurological diseases as Creutzfeldt-Jakob disease.

F Prevention and Treatment

Controlling the spread of infectious animal diseases begins with isolating, or quarantining, animals with threatening infections, such as salmonella, to prevent further transmission. Many bacterial diseases can be treated with various antibiotics, such as penicillin and streptomycin. But as with all disease, prevention is more important than treatment, and a major activity for veterinarians is immunization of animals. Immunization commonly involves an injection of a weakened or killed pathogen for a specific disease that encourages the immune system to fight off infection. Many infectious diseases, including rabies, canine distemper, feline leukemia, anthrax, and brucellosis, can be prevented by immunization. In the case of severe outbreaks of infectious disease, public health officials may work with animal owners to destroy large groups of animals. This was the case in the early 1990s, when an outbreak of bovine spongiform encephalopathy triggered the slaughter of many beef cattle in Britain.

Transmission of animal diseases to humans is a constant concern of public health officials. To protect people from disease, veterinarians inspect food animals for wholesomeness; quarantine and examine animals brought into the United States from other countries; test animals for the presence of disease; and actively work to prevent and eradicate diseases that threaten human health.

III NONINFECTIOUS DISEASES

Even if it were possible, a world without pathogens would not be disease-free. Many animal diseases are caused by noninfectious factors such as an animal's environment, genetics, and nutrition. Heatstroke, for example, occurs when an animal is forced to endure high temperatures without access to water, adequate ventilation, or suitable shade. A common scenario involves an animal that has been locked inside a car without air-conditioning during hot weather. Conversely, extreme cold can lead to hypothermia or frostbite. Other environmental hazards include the vast array of products humans use to eliminate pests and weeds from homes, farms, and gardens. For example, rodenticide, poison used to kill rats and mice, can cause fatal internal hemorrhaging in any animal that ingests this toxic substance. Improper use of flea powders, sprays, dips, and collars can also cause illness. Automobile antifreeze is another well-known poison. Its sweet taste appeals to some animals, such as cats and dogs, but consuming only a small amount can result in death. Many plant species are also toxic to animals. Some, such as pokeweed and yew, commonly grow in pastures and yards.

Poor feeding practices can lead to diseases such as nutritional secondary hyperparathyroidism, a condition involving the muscles and bones of dogs that is associated with an all-meat diet. Large, rapidly growing puppies that consume too many calories and too much calcium can develop hypertrophic osteodystrophy, a disease resulting in lameness. Cats need sufficient amounts of an essential amino acid called taurine in their diets. Without it, they may develop eye problems. Not enough iodine intake can cause a goiter, or enlargement of the thyroid gland, in cows, horses, and other animals.

Trauma is a leading cause of injury and premature death in animals, especially pets that are allowed to roam free outdoors. Many animals are hit by cars or bitten by other animals. Farm animals may be attacked by predators, or they may harm themselves on sharp fencing or discarded nails. Untreated wounds can become infected and cause permanent damage.

Hip dysplasia, a painful and debilitating skeletal condition, is a noninfectious disease caused in part by heredity. Certain defects of the heart or palate, the roof of the mouth, may also be inherited. Some animals are genetically predisposed to diseases such as generalized demodectic mange, a skin disease caused by mites and characterized by hair loss and scaling around the eyelids, mouth, and front legs.

An animal's immune system is designed to detect and eliminate invading organisms. Occasionally, however, it behaves as though the animal's own body were the attacker, and it destroys healthy tissue. Diseases caused by this response, known as autoimmune diseases, include pemphigus foliaceous, a skin disease of dogs, cats, and horses; and rheumatoid arthritis, a severe type of arthritis that involves inflammation of the joints. In the autoimmune disease hemolytic anemia, the animal's own red blood cells are destroyed by its immune system.

Cancer exists in all animals. It is classified as either benign—that is, relatively noninvasive and unlikely to return after treatment; or as malignant—that is, aggressive and likely to spread. Any organ or system can be affected, either directly or through metastasis—when cancer cells from one part of the body spread to other areas of the body. Some forms of cancer are more widespread in animals of a particular breed, age, or sex, and even individuals of a specific color. For example, cancer of the mammary gland occurs more often in female animals, while melanoma, or skin cancer, is the most frequent tumor of elderly gray horses, and lymphosarcomas, tumors of the lymph nodes, are the most common type of specific tumor in cats. The study of cancer, known as oncology, is a growing field in veterinary medicine.
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