Aminoglycoside serum concentration sampling via central venous catheters: a potential source of clinical error

Two patients receiving aminoglycosides via central venous Silastic catheters were noted to have serum drug concentrations markedly divergent from expected results. Study of these patients, and of four additional patients prospectively selected for study, demonstrated that three of five patients had higher peak and/or trough aminoglycoside serum concentrations--when blood was obtained from the central venous catheter--than were contained in simultaneous samples from peripheral blood; these divergent results were noted after the catheter had been in use for more than 1 week; divergent results were not improved by additional catheter flushing prior to central venous blood sampling. These observations suggest that spurious aminoglycoside serum concentration results may sometimes be obtained when blood sampling is performed from central venous Silastic catheters, and can result in improper drug dosage alterations. It is necessary to access the timing, processing, and reliability of serum drug-monitoring practices on a routine basis to preclude such problems, and to reassess individual patient-monitoring studies which are inconsistent with anticipated results.