Adverse drug reactions - basic principles

Any drug that is capable of producing beneficial therapeutic effects can also cause unwanted ‘adverse’ effects. Adverse drug reactions (ADRs) are therefore common and constitute an important public health challenge in their own right. A significant proportion of admissions to hospital are caused by ADRs and hospitalised patients frequently experience ADRs that complicate and prolong their stay. Many of these ADRs can be avoided if greater care is taken. All prescribers need to make a judgment about the likelihood that a patient will either gain from the beneficial effects or experience an ADR before prescribing. Some drugs rarely cause ADRs (e.g. paracetamol) while others frequently do so (e.g. cancer chemotherapy). The decision to prescribe these ‘higher risk’ drugs will depend on the extent of the potential benefits. Although prescribers always face the possibility of causing an ADR the risks of doing so can be minimised by (i) recognition of patient and drug factors that increase the susceptibility and (ii) by counselling patients about early indications that an ADR may be developing.