Elevations of urinary pH may lower vancomycin serum concentration.

Abstract This study investigated endogenous factors that may increase the elimination of vancomycin (VCM) in adult methicillin-resistant Staphylococcus aureus (MRSA) patients with pneumonia. 48 patients (32 men and 16 women) admitted to the National Hospital Organization Kumamoto Medical Center for pneumonia due to MRSA were evaluated. VCM (500 - 2,000 mg/dose) was administered intravenously for 60 - 120 min at 8- - 12-h intervals. The dose of VCM prescribed was determined based on the treatment guidelines of the Infectious Diseases Society of America and was dependent on a patient's creatinine clearance. Univariate analysis identified that potassium value (K) (p = 0.081) and urinary pH (p = 0.026) were possibly associated with decreased VCM concentration. Multivariate analysis confirmed that urinary pH was an independent risk factor for VCM clearance (p = 0.029). VCM clearance in patients with a urine pH of 8 was significantly higher (p = 0.032) than in patients with a urinary pH of 5. As urinary pH increased in alkalinity, a greater decrease in VCM concentrations was observed. Elevation of urinary pH promotes the urinary excretion of VCM, likely by promoting the dissociation of the carboxyl group of VCM. Thus, in the clinical setting, urinary pH should be measured and considered when determining dosage, as it may affect the VCM blood concentration.