Predictors of serum vancomycin levels in peritoneal dialysis-associated peritonitis

Intraperitoneal (IP) vancomycin is often first-line empiric therapy for peritoneal dialysis (PD) peritonitis; however, whether dosing should be adjusted for patient-specific characteristics remains unclear. We sought to identify factors associated with the day 3 vancomycin serum level in patients receiving vancomycin for PD peritonitis.

Retrospective single-centre adult cohort of 58 patients with PD peritonitis treated with IP vancomycin between January 2016 and May 2022. Linear regression was used to examine the association between day 3 vancomycin level and candidate predictors including age, sex, weight, glomerular filtration rate (GFR), urea and creatinine clearance (total, residual, dialysate), PD modality, peritoneal solute transfer rate and initial vancomycin dose. Logistic regression was used to evaluate the likelihood of achieving a level (≥15 mg/L) associated with these predictor variables.

A 2-g loading dose was given in 51 cases, and 38 patients (66%) had a therapeutic day 3 level. Each 5 mg/kg increase in initial vancomycin dose was associated with a 1.38 mg/L (95% confidence interval 0.52, 2.23) increase in day 3 level. Each 1 mL/min increase in GFR was associated with a 0.29 mg/L decrease (95% confidence interval 0.05, 0.52) in day 3 level. The likelihood of achieving a therapeutic level was approximately four times higher with an initial dose of ≥25 mg/kg compared to <25 mg/kg (odds ratio 3.75, 95% confidence interval 1.05, 13.46).

Following an average 2-g vancomycin loading dose for suspected PD peritonitis, one-third of patients were subtherapeutic on day 3. GFR and weight-based dosing were independently associated with day 3 vancomycin level, and their consideration could improve the likelihood of achieving an early therapeutic level.