Proper recognition and resolving the problem of drug-drug interaction are one of the most essential issues in pharmaceutical care. The paper concerns the problem of drug-drug interactions with the special attention toward the interactions that are important for pharmacists working in the community pharmacies.

The mechanism of clinically relevant pharmacokinetics and pharmacodynamics drug-drug interactions are presented. Moreover, the paper focuses on the interactions based on cytochrome P450. Special attention is given toward those interactions which include inhibition and induction of the most important isoforms of CYP450: CYP3A4 and CYP2D6. The examples of clinically important well documented interactions involving those isoforms are presented.