drug interactions
the effects of administering two or more drugs concurrently, which alters the pharmacological action of one or more of them. Pharmacokinetic interactions alter the absorption, distribution, metabolism, and excretion of the drugs; they may induce or inhibit the elimination of these drugs, leading to unexpected increases or decreases in their concentrations in the body. Pharmacodynamic interactions affect the drugs’ activities at target organs or receptor sites; they may be synergistic, enhancing the effectiveness of a drug at a target receptor or organ (see drug synergism), or antagonistic, in which the presence of one drug reduces the effectiveness of another (see antagonist).