II. Reading. Drugs are chemical substances used in medicine in the treatment of diseases

Drugs

Drugs are chemical substances used in medicine in the treatment of diseases. These chemical substances can come from many different sources. Drugs are obtained from various parts of plants, such as the roots, leaves, and fruit. Examples of such drugs are digitalis (from the foxglove plant), and antibiotics such as penicillin and streptomycin (from plants called molds). Drugs can also be obtained from animals; for example, hormones are secretions from the glands of animals. Drugs can be made from chemical substances which are synthesized in the laboratory. Anticancer drugs, such as methotrexate and predni­sone, are examples of laboratory-synthesized drugs. Some drugs are contained in food substances; these drugs are called vitamins. Drugs are dispensed and stored in an area known as a pharmacy.

The field of medicine which studies drugs, their nature, origin, and effect in the body is called pharmacology. Pharmacology is a large medical specialty and contains many subdivisions of study, including pharmacodynamics, molecular pharmacology, clinical pharmacology, pharmacogenetics, chemotherapy, toxicology and others.

Pharmacodynamics involves the study of how drugs exert their ef­fects in the body. Scientists interested in pharmacodymanics study the processes of drug absorption (how drugs pass into the bloodstream), metabolism (changes drugs undergo within the body) and excretion (removal of the drug from the body).

Molecular pharmacology concerns the study of the interaction of drugs and cells or subcellular entities, such as DNA, RNA, or en­zymes. These studies provide important information about the mecha­nism of action of the drug.

Clinical pharmacology is a medical field of medication effect on humans.

Pharmacogenetics deals with clinical testing of genetic variation that gives rise to different responses to drugs.

Chemotherapy is the subdivision of pharmacology, which studies drugs that are capable of destroying microorganisms, parasites, and cells within the body without destroying the body itself. Chemotherapy includes treatment of infectious diseases, mental illnesses, and cancer.

Toxicology is the study of harmful chemicals and their dangerous effects on the body. Toxicology includes the study of the potentially harmful effects of any drug on the body; any drug, if given in high enough doses, can have harmful actions on the body. Toxicological studies in animals are required by law before new drugs can be tested in individuals. A toxicologist is also interested in finding proper anti­dotes to these harmful effects. Antidotes are substances given to neu­tralize unwanted effects of drugs.

Drug toxicity refers to the poisonous and potentially dangerous effects of some drugs. Idiosyncrasy is an example of an unpredictable type of drug toxicity. Other types of drug toxicity are more predictable and based on the dosage of the drug given. If the dosage of certain drugs is increased, unfavorable effects may be produced. Physicians are trained to be aware of the potential toxic effects of all drugs they prescribe and must be cautious with their use.

Side effects are toxic effects which routinely result from the use of a drug. They often occur with the usual therapeutic dosage of a drug and are usually tolerable. For example, nausea, vomiting, and alopecia are common side effects of the chemotherapeutic drugs used to treat cancer.

Contraindications are the factors in the patient's condition which make the use of a drug dangerous. Among the most dangerous toxic complications of drug usage are blood dyscrasias (blood diseases) such as aplastic anemia and leukopenia, cataract formation (eye disorder), cholestatic jaundice (biliary obstruction leading to yellow discoloration of skin), neuropathy, collagen disorders (connective tissue damage such as arthritis), and photosensitivity (abnormal sensitivity to light).

III. Language development

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