Determination of serum gentamicin sulfate levels: ordering patterns and use as a guide to therapy

Determination of serum gentamicin levels (SGLs) is helpful in monitoring therapy in patients receiving this drug because there is a narrow therapeutic margin and serum levels may vary greatly between patients receiving similar doses. During a ten-month period, definite indications for obtaining SGL determinations were present for 189 of 212 serum samples (89.2%) submitted to the laboratory. However, 110 samples (51.9%) were improperly drawn and results of 85 samples (40.1%) were ignored. Only 26 of the 62 correctly drawn and not ignored samples (41.9%) were appropriately acted on. At most, 42 of the 212 samples (19.8%) were appropriately used in making patient-care decisions. Thus, in this study, an inordinatley large number of SGLs were incorrectly drawn, apparently ignored, or inappropriately used in making patient-care decisions.