Half-life prediction in unstable renal function: its utility in therapeutic drug monitoring and theoretical and practical considerations.

A simple equation is derived to describe the changes in drug elimination half-life (t1/2) in correspondence to the changes in renal function (as measured by creatinine clearance). This equation can be utilized to predict the t1/2 at any time following an initial period in patients with unstable renal function provided that the initial t1/2 and renal function corresponding to each period are known. The clinical application of this equation in predicting 21 serum gentamicin concentrations (SGC) was evaluated in patients with unstable renal function. Excellent correlation (coefficient of determination, r2 = 0.88) between the predicted and measured SGC was obtained.