Drug Interactions

INTRODUCTION A drug interaction is a pharmacological response which cannot be explained by the action of a single drug but may be due to two or more drugs acting simultaneously but The effects of a drug may also be changed by the presence of food, drink or by some environmental chemical agent. The outcome of a drug interaction may be harmful if the interaction results in increased efficacy or toxicity of one or more drugs. However, reduction in efficacy due to a drug interaction can sometimes be just as harmful.1,2 The clinical relevance of drug interactions is evident when one considers that up to 8% of hospital admissions are due to adverse drug reactions and over 20% of these are due to drug interactions.3 The incidence of drug interactions is difficult to quantify as this may depend on the “clinical significance” of the interaction.1 However the greater the number of drugs taken inevitably increases the risk of a drug interaction occurring.1