Estimation of safe and effective dose of vancomycin in MRSA-infected patients using serum cystatin C concentrations.

OBJECTIVE: To utilize serum cystatin C (CysC) concentration to identify the daily dosage regimen of vancomycin (Van) for the treatment of patients with methicillin-resistant Staphylococcus aureus (MRSA) infections.
METHODS: Serum Van, CysC, and serum and urine creatinine (Cr) concentrations were detected in 65 MRSA-infected patients. The estimated glomerular filtration rate (eGFR), Cr clearance (CLcr) and Van clearance (CLvan) were calculated and the correlation equation between CysC and CLvan was obtained using mathematical methods. Finally, the daily dosage equation of Van was derived according to pharmacokinetic theory.
RESULTS: In the test sample, serum Cr was 183.27 ± 68.34 μmol/l, CLcr was 75.56 ± 30.02 ml/min, eGFR was 70.79 ± 40.79 ml/min, and serum CysC was 1.35 ± 0.61 mg/l. There was significant correlation between eGFR and CLcr (R2 = 0.8051, p = 0.000). Bland-Altman analysis showed an agreement of 96.9% (63/65) between eGFR and CLcr. eGFR was significantly correlated with CLvan (R2 = 0.8465, p = 0.000) and the correlation was significantly higher than that between CLvan and CLcr (R2 = 0.6367, p = 0.000). CysC fits a high correlated CLvan estimating equation (R2 = 0.9211, p = 0.000): CLvan(ml/min) = 64.4026 × (CysC)-1.1488. Accordingly, the predicted equation was created for calculation of the Van dosage to achieve the appropriate target steady-state serum concentration (Css): IR (the rate of continuous infusion, g/D) = 64.4026 × (CysC)-1.1488 × Css (mg/l) × (60/1,000) × 24.
CONCLUSIONS: Serum CysC is a good marker of renal function in comparison with serum Cr for the dose determination of Van. CysC can estimate the daily dose of Van, and may improve therapeutic success rates of MRSA-infected patients.