Potential applications of free drug level monitoring in cardiovascular therapy.

Cardiovascular drugs, as a class, have low therapeutic indices, but also have great therapeutic potential. Plasma concentration information is therefore often of value when using these drugs. Unfortunately, the total plasma concentration may not reflect the concentration of pharmacologically active free drug, since a number of factors including disease states, heparin anticoagulation, non-linear binding characteristics, and in vitro artefacts can affect the protein binding of these agents. This may also explain their poor dose-response relationships and great interindividual variability in plasma concentration data. Careful studies relating bound and free drug concentration to pharmacological response may provide the clinician with a better guide to therapy, and enhance the usefulness of these drugs.