Class effects and evidence-based medicine.

Drugs grouped into a therapeutic class on the basis of a common mechanism of action often have considerably different pharmacodynamic and pharmacokinetic properties. Among angiotensin-converting enzyme (ACE) inhibitors, differences with potential clinical relevance include potency, whether the drug is an active compound or requires metabolic activation, lipophilicity, route(s) of elimination, and half-life. Large clinical trials have documented the clinical benefits of several ACE inhibitors in various patient populations, and many clinical effects of ACE inhibitors are likely to be the same. However, there are possible quantitative differences among ACE inhibitors that may alter the overall therapeutic benefits for specific patient populations and indications. Equipotency in terms of clinical efficacy is difficult to determine. Since the concept of "class effect" is a term of convenience that has no universally accepted definition and subsequently should not form the basis for the practice of evidence-based medicine, untested drugs of a "class" should be considered to be unproven drugs.