[Assessment of Renal Function and Simulation Using Serum Cystatin-C in an Elderly Patient with Uncontrollable Plasma...

Herein, we describe a case of an elderly patient with muscular dystrophy for whom control of the plasma vancomycin (VCM) concentration proved difficult when he developed a catheter-related bloodstream infection. The pharmacist initially carried out therapeutic drug monitoring using an estimate of the creatinine clearance (CL_cr) level, which was based on the serum creatinine (SCr) and serum cystatin-C (CysC) levels, but was ultimately unable to control the plasma VCM concentration. Therefore, the plasma VCM concentration was predicted ex post facto using population pharmacokinetic parameters as a covariate; that is, directly including the glomerular filtration rate (GFR_CysC) estimated from the CysC level, which is not affected by the muscle mass. As a result, the estimated VCM concentration was closer to the actual concentration than that predicted using CL_cr. Furthermore, the results of examining the predictive accuracy according to the assessment of renal function at the time of initial VCM administration suggested that estimation of the trough concentration using GFR_CysC might be useful in elderly patients with muscular dystrophy.