Drug Interactions I: How They Occur

Medication use is extensive in developed countries: it has been estimated that approximately four fifths of US adults use at least one medication (prescription medicine, over-the-counter (OTC) drug, herbal remedy) per week, and this rate increases with age. A recent US survey reported an average of 2.3 medications prescribed or provided per patient visit. A study carried out in Ireland noted that, during 2001-2002, up to 45% of patients >70 years were receiving >5 concomitant medications. The concomitant use of more than one medication leads to the potential for drug interaction which is said to occur when the response of a patient to a drug is changed by the presence of another drug, food/drink, herbal substance or some environmental agent. This is the first of 2 bulletins on drug interactions; it will explain the various ways that a drug interaction may occur, and describe ways of preventing or minimising their impact on the patient.