Among drug-drug interactions, pharmacokinetic drug interactions are those in which multiple drugs interact to produce fluctuations in their blood concentrations, and mainly involve drug-metabolizing enzymes (cytochrome P450, UDP-glucuronyltransferase) and drug transporters (P-glycoprotein, etc.). The risk of drug interactions along with an increase in the number of drugs being used simultaneously; therefore, it is important to know the mechanisms of drug interactions, and the drugs to be wary of, as well as to make efforts to reduce the number of drugs used as much as possible.