Severely Prolonged Vancomycin Half-life in a Patient with Normal Serum Creatinine and Creatinine Clearance

Vancomycin remains the antibiotic of choice to treat resistant Gram-positive infections and is dosed utilizing weight-based protocols or pharmacokinetic calculations. Pharmacokinetic calculations are a more proactive approach to vancomycin dosing but are occasionally limited as certain patient-specific variables such as volume of distribution, renal function, and severity of illness do not allow all patients to follow population estimates. In these situations, if the above-mentioned variables are adjusted for an individual patient rather than the population estimates, the kinetic models reflect accurate vancomycin dosing. We present a patient with apparently normal renal function (Cockcroft-Gault) following a significant renal injury who had sustained supratherapeutic vancomycin serum concentrations and a calculated peak elimination half-life of 346 h. Importantly, this patient had adequate clearance of other highly renally eliminated medications (digoxin and meropenem), which suggests limited long-term deficit due to the previous sustained renal injury. In this patient case, vancomycin’s chemical properties and pharmacokinetics are explored to best explain the patient’s highly unusual response. In addition, an analysis of vancomycin’s less well-described pharmacokinetics such as active secretion, tubular reabsorption, and nonrenal elimination pathways is explored. Ultimately, this patient represents a perplexing case which highlights the continued need for therapeutic drug monitoring with vancomycin.