Gentamicin blood levels: ordered too soon and too often

Records of 100 consecutive patients in whom gentamicin blood levels (GBLs) had been measured were reviewed to assess the relation between GBL, disease course, and outcome. Thirty-two patients discontinued treatment, 16 within 72 hours because of negative cultures or improved clinical course, and 16 within 96 hours because susceptibility tests indicated that another antibiotic would be more appropriate. Of the remaining 68 patients who continued treatment, 21 recovered from their infection despite low peak or low peak and trough gentamicin levels, at least partially attributable to treatment with multiple antibiotics. Renal function deteriorated in only 1 of 10 patients with normal renal function and a high GBL. Our findings of early discontinuation of gentamicin, low concentrations with good outcome, and rare nephrotoxicity indicate wasteful overuse of GBLs. To decrease patient care costs without adversely affecting outcome, gentamicin measurements should be delayed for 72 to 96 hours--until culture results become available--except in patients with decreased renal function, documented gram-negative sepsis, leukopenia, or severe burns.