Correlation of Serum Creatinine Concentration and Gentamicin Half-Life

The serum half-life of gentamicin sulfate following an intravenous dose was compared to the serum creatinine concentration in 21 adult patients with different degrees of renal failure. A correlation was found such that the gentamicin half-life (in hours) could be estimated by multiplying the serum creatinine concentration (mg/100 ml) by four. The apparent distribution volume for gentamicin is about 24% of the body weight, but may be larger in patients with renal insufficiency. An injection of 2 mg/kg of body weight will result in therapeutic drug levels. Kinetic analysis predicts that repetition of this loading dose every third half-life will result in therapeutic, nontoxic serum levels in patients with renal failure. An alternate approach using a constant dose interval but varying the quantity of drug can be predicted from a nomogram.