ABSTRACT
Pharmaceutical interactions occur by chemical reaction or physical interaction when drugs are mixed. Pharmacodynamic interactions occur when different drugs each infuence the same physiological function (e.g. drugs that influence state of alertness or blood pressure); the result of adding a second such drug during treatment with another may be to increase the effect of the first (e.g. alcohol increases sleepiness caused by benzodiazepines). Conversely, for drugs with opposing actions, the result may be to reduce the effect of the first (e.g. indometacin increases blood pressure in hypertensive patients treated with an antihypertensive drug such as losartan). Pharmacokinetic interactions occur when one drug affects the pharmocokinetics of another (e.g. by reducing its elimin-ation from the body or by inhibiting its metabolism). These mechanisms are discussed more fully below in the section on adverse interactions grouped by mechanism. A drug interaction can result from one or a combination of these mechanisms.
