Drug concentrations. A guide to their usefulness in clinical practice.

When used properly, measurements of plasma drug levels in the clinical setting may provide valuable information. Optimally the drug level will permit the clinician to devise a therapeutic regimen on the basis of an individual patient's handling of the drug and thus obtain maximal drug efficacy while minimizing the risk of drug toxicity. However, the technology that permits the measurement of drug levels has often outpaced the clinical data base that allows proper interpretation of the level. Thus, the physician should be aware of both the potential and the limitations of therapeutic drug monitoring and apply the technique critically with respect to individual drugs in individual patients.