[Assessment of Renal Function and Simulation Using Serum Cystatin-C in an Elderly Patient with Uncontrollable Plasma Vancomycin Levels Due to Muscular Dystrophy: A Case Report].

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 (CLcr) 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 (GFRCysC) 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 CLcr. 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 GFRCysC might be useful in elderly patients with muscular dystrophy.