Misuse of therapeutic drug monitoring: an analysis of causes and methods for improvement.
The quantification of serum drug levels provides physicians with an indication of attainment of the desired pharmacologic goals. However, based on the preceding evidence, therapeutic drug monitoring (TDM), which is commonly used in conjunction with the prescribing of anticonvulsants, antiarrythmics, cardiac glycosides, antibiotics, antineoplastics, bronchodilators, lithium, antidepressants, neuroleptics, benzodiazepines, and other psychotropic drugs, is not used effectively for therapeutic intervention in the elderly. In addition to determining if a blood level is within the therapeutic range, TDM can also be helpful in identifying the reasons why a patient is not responding to a prescribed drug or is exhibiting toxic signs or symptoms, as well as in elucidating causes of coma, patient noncompliance, poor absorption, and excessively rapid metabolism. Furthermore, drug blood levels can be an asset in the diagnosis and monitoring of treatment programs for alcohol and drug abuse. Despite the existence of computerized programs for drug level determination in clinical laboratories, and the existence of individualized computer programs for optimizing the choice and dosage of drugs for many categories of patients with a multitude of metabolic and pathophysiologic problems, most physicians still rely on tradition, imitation, and information provided by drug advertising and sales representatives to choose therapeutic regimens for patients. To make proper use of TDM, a physician has to have at least a working knowledge of the basic concepts of pharmacokinetics. This advancing medical science also demands a thorough knowledge of the routes of absorption, distribution, metabolism, and excretion of drugs. Results from TDM determinations indicate how effectively the appropriate amount of drug is delivered to the desired location of action from the site of administration. One of the most common reasons for misuse of TDM results is that physicians order specimens for drug monitoring to be drawn at inappropriate times. Accurate TDM requires that (most) specimens be drawn at trough levels, after steady-state levels have been attained. Trough levels occur immediately prior to the administration of the next dose. Such measurements avoid the absorptive peaking levels that occur shortly (usually) after drug administration. Steady-state levels are attained when the amount of drug absorbed and the amount excreted are essentially equal. This usually occurs after the drug has been administered for approximately five half-lives.(ABSTRACT TRUNCATED AT 400 WORDS)
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D006801:Humans; D008991:Monitoring, Physiologic / Q000706:statistics & numerical data*; D004364:Pharmaceutical Preparations / Q000032:analysis*
D004364:Pharmaceutical Preparations