Drug Interactions

Abstract

Drug interaction is the alteration of the effect of one drug due to the concomitant or prior presence of another drug. Drug interactions represent a major preventable cause of adverse drug interactions. Factors which predispose to drug interactions include increasing age, polypharmacy, liver disease, kidney disease, and environmental and food interactions. In vitro interactions occur rarely when the drugs are mixed in a solution before administration intravenously. The two types of in vivo interactions are pharmacokinetic and pharmacodynamic interactions. Alteration of gastric pH, gastrointestinal motility, gut flora, and chelation represent interactions which can happen at the level of drug absorption stage. At the level of distribution, one drug can displace another from protein binding sites. The induction and inhibition of liver enzymes by one drug that metabolizes other drugs are one of the major reasons behind drug interactions. At the level of drug excretion, a drug can affect tubular secretion and reabsorption of other drugs. These interactions can be further classified as additive, synergistic, or antagonistic. In many instances, we have successfully employed drug interactions for our benefit.