TERMINOLOGY OF DRUG ACTION

There are certain terms which describe the action and interaction of drugs in the body. These terms are listed below with explanations of their meanings:

Potentiation (Synergism). Sometimes a combination of two drugs can cause an effect which is greater than the sum of the individual effect of each drug alone. For example, penicillin and streptomycin, two antibiotic drugs, are given together in treatment for bacterial endocarditis because of their synergistic action.

Additive Action. In this drug action, the combination of two similar drugs is equal to the sum of the effects of each. For example, if drug A gives 10 per cent tumor kill as a cancer chemotherapeutic agent and drug В gives 20 per cent tumor kill, using A and В together would give 30 per cent tumor kill. If these drugs were synergistic in their action, a combi­nation of drugs would give greater than 30 per cent tumor kill.

Cumulation. If a drug is given in short intervals and the body cannot dispose of it rapidly enough, the drug concentration will rise in the body tissues with each successive dose. This cumulation may cause toxic ef­fects in the body. There are some instances, however, in winch cumulation is desired for therapeutic purposes: the use of digitalis in management of cardiac insufficiency is an example of a therapeutic buildup of a drug to promote the efficient working of the heart.

Tolerance. In this drug action, the effects of a given dose diminish as treatment goes on, and larger and larger doses are needed to pro­duce desired effect.Tolerance is a feature of addiction to drug (f.e. morphine).

Idiosyncrasy. In some instances, a patient may display unexpected effects following the administration of a drug. Idiosyncratic reactions are produced in very few patients taking a drug, but may be life-threatening in those few instances. For example, in some individuals penicillin is known to cause an idiosyncratic reaction such as anaphylaxis (acute type of hypersensitivity, including asthmaand shock).