Contraindication

A contraindication is a specific clinical situation in which a medicine should not be administered because the expected harm outweighs any potential benefit. Contraindications are typically listed in the prescribing information following the boxed warning (if any) and are divided into two categories: absolute contraindications (the medicine must not be used under any circumstances in this scenario) and relative contraindications (the medicine should be avoided unless the benefit clearly outweighs the risk, with extra precaution and monitoring).

Examples of absolute contraindications include the use of ACE inhibitors or ARBs in pregnancy due to known fetal renal malformations and oligohydramnios; the use of beta blockers in severe asthma exacerbation; the use of NSAIDs in severe heart failure or active GI bleeding; the use of MAO inhibitors with serotonergic medicines because of the risk of life-threatening serotonin syndrome; the use of triptans in patients with recent myocardial infarction or uncontrolled hypertension; and the use of fluoroquinolones in pregnant patients and pre-pubertal children, traditionally avoided because of concerns about cartilage damage.

Relative contraindications are softer and depend on clinical judgment. Metformin should generally be avoided in patients with significantly reduced kidney function due to the risk of lactic acidosis, but the cutoff has shifted over time as evidence has matured. Statins are used cautiously in patients with active liver disease. Beta blockers may be used with care in mild asthma if a cardioselective agent is chosen.

Clinically, contraindications form the backbone of pharmacy verification and clinical decision support systems. Electronic health records flag prescribing attempts that violate documented contraindications - a patient with a documented penicillin allergy receiving amoxicillin, a pregnant patient receiving warfarin, or a patient on an MAO inhibitor receiving meperidine. These alerts have reduced major prescribing errors but also contribute to alert fatigue when overused.

A common misconception is that a contraindication is a polite suggestion. It is not - prescribing a medicine despite an absolute contraindication is considered medical error and a deviation from the standard of care unless extraordinary circumstances and informed consent are clearly documented. Another misconception is that contraindications are permanent. Many contraindications are condition-dependent and resolve when the underlying issue resolves (postpartum status, recovery of kidney function, resolution of liver disease).

Prescribers should review the prescribing information for all relevant contraindications before initiating a new medication, particularly in pregnancy, pediatrics, geriatrics, organ failure, and polypharmacy contexts. Documentation of the rationale for proceeding when a relative contraindication exists protects both patient and clinician.