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drugs; substances used in the treatment or prevention of diseases. Before the 19th century fresh products or products of vegetable, animal, or mineral origin subjected to relatively simple processing were used as drugs. As chemistry developed, the active principles were isolated from these raw materials, the chemical structures were established, and drugs were synthesized. Analogues and homologues of natural alkaloids, hormones, and other substances were obtained through the study of the connection between chemical structure and pharmacological effect. Elucidation of the mechanisms of action of medicines promoted the purposeful search for new and effective preparations. Before a medicine is adopted by medical practice, it undergoes detailed study, first in experiments on animals and then under clinical conditions.
Medicines may be classified according to chemical structure, influence on physiological systems, sphere of use, or main form of action. Usually a mixed classification using various criteria is preferred. For example, narcotics, neuroleptics, analgesics, spasmolytics, cardiovascular agents, diuretics, laxatives, hormonal preparations, and other medicines designated for the specific treatment of infectious diseases are conventionally called chemotherapeutic agents.
Depending on the effect desired, medicines are introduced into the body by various means: internally, subcutaneously, topically, intramuscularly, intravenously, or by inhalation. Each of these methods requires a special form of the preparation: solution, powder, tablet, or ointment.
With repeated use, a medicine sometimes has a cumulative effect, either as a result of accumulation of the drug in the body or a summation of effects. Attenuation of the effect is also possible. With certain medicines, repeated use may bring about craving and habituation (drug addiction). Individual sensitivity to a medicine is sometimes observed (idiosyncrasy).
The most important medicines, approved in every country, are entered in the Pharmacopoeia with descriptions of their chemical and physical properties, quality determinations, and maximal dose indications.
REFERENCESMashkovskii, M. D. Lekarstvennye sredstva, 7th ed., parts 1–2. Moscow, 1972.
Zakusov, V. V. Farmakologiia, 2nd ed. Moscow, 1966.
Kalashnikov, V. P. Rukovodstvo po retsepture, 2nd ed. [Leningrad] 1954.