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Related to drug action: pharmacodynamics, Mechanism of drug action
Local: When the drug is applied locally or directly to a tissue or organ, it may combine with the cell's membrane or penetrate the cell. Its action may be (1) astringent when the drug causes the cell or tissue to contract, (2) corrosive when the drug is strong enough to destroy cells, or (3) irritating when too much of the drug combines with cells and impairs them.
General, or systemic: This type of action occurs when the drug enters the bloodstream by absorption or direct injection, affecting tissues and organs not near the site of entry. Systemic action may be (1) specific, when it cures a certain disease; (2) substitutive or replenishing, when it supplies substances deficient in the body; (3) physical, when some cell constituents are dissolved by the action of the drug in the bloodstream; (4) chemical, when the drug or some of its principles combine with the constituents of cells or organs to form a new chemical combination; (5) active by osmosis, caused by dilution of salt (also acids, sugars, and alkalis) in the stomach or intestines by fluid withdrawn from the blood and tissues; or by diffusion, when water is absorbed by cells from the lymph; (6) selective, when action is produced by drugs that affect only certain tissues or organs; (7) synergistic, when one drug increases the action of another; (8) antagonistic, when one drug counteracts another; (9) physiological, when the drug exerts a potentially beneficial effect similar to that which the body normally produces; (10) therapeutic, when the effect is to treat or repair diseased organs or tissues; (11) side active, creating an undesired effect; (12) empirical, producing results not proved by clinical or laboratory tests to be effective; or (13) toxicological, having a toxic or undesired effect, generally the result of overdose or long-term usage.
Cumulative: Some drugs are slowly excreted or absorbed so that with repeated doses an accumulation in the body produces a toxic effect. Such drugs should not be administered continuously.
Incompatible: Undesired side effects occur when some drugs are administered together. This may be due to the antagonistic action of one drug on others or to a physical interaction of the drugs that inactivates one of them (e.g., precipitation of some drugs mixed in intravenous fluids).