Drug interactions.

Drug interactions have been implicated in approximately 7 percent of all reported adverse drug reactions. Although many drug interactions are not clinically significant, the potential for an interaction increases from 5.6 percent in patients receiving two drugs to 100 percent in patients receiving eight or more drugs. Drug interactions can involve alterations in the pharmacokinetic parameters of absorption, distribution, metabolism and excretion, or can result from cumulative or antagonistic effects.