Use of serum drug concentrations in surgical patients.

Surgical patients frequently require drug treatments that can be assessed with serum drug concentrations. Of the agents for which serum drug concentrations are routinely available, the aminoglycosides theophylline, vancomycin, digoxin, and phenytoin are used most frequently in surgical patients. When using serum drug concentrations, the clinician should have an understanding of the relationships (or lack of) between drug concentrations and therapeutic or toxic effects. When blood is collected for serum concentration determinations, the exact timing of the sample in relation to the dose must be considered. For some drugs, (such as the aminoglycosides, it is necessary to determine peak and trough concentrations, whereas for other agents, like theophylline, the average or mid-dose level may be more important to consider. There are many factors that affect serum drug concentrations. Among these are various disease states, obesity, fluid imbalances, the drug dosage form used, and concurrent drug use. Not all patients require serum drug concentration monitoring; however, with each drug there are high-risk patients who may benefit. When used properly, serum drug concentrations may be helpful in maximizing therapeutic benefits, minimizing or diagnosing drug toxicity, and assessing patient compliance with drug regimens.