Drug Interactions and Their Management

With the increasing prevalence of polypharmacy, it is more important than ever to consider the possibility of drug–drug interactions. A drug–drug interaction occurs when the way in which a drug works is altered by the presence of another drug. Interactions can also occur between drugs and other substances contained in herbs, supplements, food, and smoking. Further drug interactions can include drug–disease and drug–laboratory test interactions. Drug–drug interactions can be classified into two main categories: pharmacokinetic and pharmacodynamic. Pharmacokinetic drug interactions occur when one drug alters the rate or extent of absorption, distribution, metabolism, or excretion of another drug. Many drug interactions that occur in practice are pharmacokinetic in nature, for example, those interactions affecting the metabolism of a drug through the involvement of cytochrome P450 enzymes in the liver. Pharmacodynamic drug interactions occur when the action of a drug in the body is altered by a coadministered drug. In this chapter, we will consider the mechanisms by which drug interactions occur, examine some clinically relevant drug interactions, outline how drug interactions can be managed and prevented in practice by health-care professionals, and consider the future research needs relating to drug interactions.