Adverse drug reactions

Adverse drug reactions (ADRs) affect around 5–10% of medical in-patients, and one-half of ADRs occur prior to admission. ADRs are often missed, and they should be considered in the differential diagnosis of a wide range of conditions. ADRs can be classified according to dose-relatedness, time-course, and susceptibility (DoTS). ADRs can be subdivided by dose-relatedness into toxic effects, such as nephrotoxicity with high doses of aminoglycosides; collateral effects, such as Clostridium difficile infection with broad-spectrum antibiotics; and hypersusceptibility reactions, which include anaphylactoid reactions to iodinated contrast media and acetylcysteine. Time-course patterns for ADRs are either time-dependent, as in the ‘red man syndrome’, due to rapid administration of vancomycin, or time-independent, as seen in ADRs due to drug interactions. Individuals can be susceptible to rare ADRs due to genetic variation; examples include drug-induced haemolysis in patients with glucose-6-phosphate dehydrogenase deficiency. Other factors increasing susceptibility include age, sex and certain disease states. The detection of ADRs relies heavily on spontaneous reporting (e.g. the UK Yellow Card scheme), stimulated post-marketing surveillance, and case-control studies. Detecting and reporting ADRs makes prescribing safer and more likely to achieve its aims.