Therapeutic coverage: reducing the risks of partial compliance.

It is now apparent that the incidence of inadequate compliance is greater than had previously been recognised. The pattern of poor compliance is generally characterised by underdosing rather than overdosing and will usually involve interruptions in therapy of several days. There are many potentially important consequences of this, but therapeutically the most important is associated with the period without drug action. Establishing, for a range of antihypertensive agents, that there is a clear relationship between the circulating drug concentration and blood pressure-lowering effect it is possible to demonstrate that the pharmacodynamic characteristics of a drug will be well correlated with its pharmacokinetics. Thus, compared with other agents, amlodipine with its relatively smooth concentration-time profile and long elimination half-life will be superior in maintaining blood pressure control both with perfect compliance and when dosage regimens are perturbed due to missed drug doses.