Aminoglycoside predictions using a hand-held calculator: limitations of the model

Previously published methods for determining an appropriate aminoglycoside dosage have been adapted for use in the hand-held programmable calculator (Texas Instrument-59). The purpose of this study was to evaluate the accuracy of calculator-generated serum level predictions compared with measured values. Twenty-four adult patients receiving intravenous aminoglycosides (gentamicin, netilmicin, or tobramycin) had urine and serum collected for creatinine clearance calculations and had blood obtained for peak and through aminoglycoside concentration determinations. All but one patient had normal renal function. A statistically significant relationship between predicated and measured creatinine clearance values was found. There was also generally good agreement between the calculator-predicted aminoglycoside levels and the measured levels, although some patients exhibited unexplained deviations. Error in the estimation of creatinine clearance and adjustments for lean body weight did not improve prediction accuracy. We conclude that the hand-held calculator was able to predict measured aminoglycoside levels for most patients with acceptable precision. However, the calculator method offers no real advantage over other methods (except speed in performing the calculation), and may give the user a false sense of security.