Validation of the Hartford nomogram in trauma surgery patients

OBJECTIVE: To validate the Hartford nomogram for once-daily aminoglycoside dosing in trauma surgery patients. METHODS: A chart review was performed in trauma surgery patients who were started on once-daily aminoglycoside therapy. A peak aminoglycoside concentration was drawn 30 minutes after the end of the first or second infusion, and a random concentration was drawn approximately 10 hours after the dose. The 10-hour random concentration was used to validate the Hartford nomogram by predicting the actual dosing interval (determined by extrapolating the peak and random concentrations to achieve a trough concentration <1 mg/L). The percentage of intervals accurately predicted by the nomogram was determined. RESULTS: Forty-nine patients (34 men and 15 women), age 43.0+/-15.9 y, total body weight 81.3+/-24.5 kg, ideal body weight 68.1+/-10.7 kg, dosing body weight (DBW) 72.0+/-14.4 kg, and estimated creatinine clearance [Cl(cr)] 89.5+/-20.6 mL/min/1.73 m2 were evaluated. Patients received 505+/-105 mg (7.0+/-0.4 mg/kg) of either gentamicin or tobramycin per dose. The concentration 30 minutes after the infusion was 22.4+/-5.9 mg/L, the concentration at the end of the dosing interval was 0.20+/-0.46 mg/L, the 10-hour random concentration was 2.6+/-1.8 mg/L, the elimination rate constant was 0.26+/-0.08 h(-1), the elimination half-life was 3.0+/-1.2 hours, and the volume of distribution was 19.9+/-7.9 L (0.28+/-0.09 L/kg of DBW). Ninety-eight percent (48/49) of the intervals were accurately predicted by the nomogram. CONCLUSIONS: In trauma surgery patients with Cl(cr) of more than 60 mL/min/1.73 m2, the Hartford nomogram using a single random aminoglycoside concentration accurately predicted the same once-daily aminoglycoside intervals as determined by two concentrations. Less aggressive therapeutic drug monitoring in this patient subpopulation can lead to significant cost savings.