Medicine

Medicine goes beyond the bedside of patients. Medical scientists engage in a constant search for new drugs, effective treatments, and more advanced technology. In addition, medicine is a business. It is part of the health care industry, one of the largest industries in the world and among the leading employers in most communities.

Since time immemorial, disease has played a role in the history of societies. It has affected—and been affected by—economic conditions, wars, and natural disasters. Indeed, the impact of disease can be far greater than better-known calamities. An epidemic of influenza that swept the globe in 1918 killed between 20 million and 40 million people.

Disease has been one of humanity's greatest enemies. Only during the last 100 years has medicine developed weapons to fight disease effectively. Vaccines, better drugs and surgical procedures, new instruments, and understanding of sanitation and nutrition have had a huge impact on human well being. Like detectives, physicians and other health care professionals use clues to identify, or diagnose, a specific disease or injury. They check the patient's medical history for past symptoms or diseases, perform a physical examination, and check the results of various tests. After making a diagnosis, physicians pick the best treatment. Some treatments cure a disease. Others are palliative—that is, they relieve symptoms but do not reverse the underlying disease. Sometimes no treatment is needed because the disease will get better by itself. While diagnosing disease and choosing the best treatment certainly require scientific knowledge and technical skills, health care professionals must apply these abilities in imaginative ways. The same disease may present very different symptoms in two patients, and a treatment that cures one patient may not work on another.

Physicians diagnose diseases and injuries, administer treatment, and advise patients on good diet and other ways to stay healthy.

Drugs

            Drug is a 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.

 Since 1900 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, has increased the average American’s life span from about 60 years to about 75 years. Drugs have vastly improved the quality of life. Today, drugs have contributed to the eradication of once widespread and sometimes fatal diseases such as poliomyelitis and smallpox.

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 oral administration (via mouth), injection, inhalation, or direct application to the skin (absorption).

 Drugs are also classified by their names. All drugs have three names: a chemical name, which describes the exact structure of the drug; a generic or proprietary name, which is the official medical name assigned by a council (a group composed of pharmacists and other scientists); and 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, 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. 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 metabolised, 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.

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 anaesthetics; 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 anaesthetics 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).

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. 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, metabolised, 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.