Metabolism-based cyclophosphamide dosing for hematopoietic cell transplant

Area of Science:

• Pharmacology
• Oncology
• Transplantation

Background:

• High-dose cyclophosphamide (CP) is used in hematopoietic cell transplantation (HCT).
• Increased exposure to carboxyethylphosphoramide mustard (CEPM), a CP metabolite, correlates with liver toxicity and mortality.
• Current dosing strategies do not account for individual metabolic variations, leading to unpredictable CEPM exposure.

Purpose of the Study:

• To assess the feasibility of dose-adjusting cyclophosphamide in HCT to achieve a target metabolic endpoint.
• To determine if a lower total cyclophosphamide dose, guided by metabolism, affects engraftment.

Main Methods:

• A prospective study involving 20 HCT patients.
• Administered an initial dose of 45 mg/kg cyclophosphamide.
• Collected blood samples over 16 hours to calculate the area under the curve (AUC) of CEPM (AUC(CEPM)) using noncompartmental analysis.
• Estimated the 0-48 hour AUC(CEPM) and adjusted the second CP dose to reach a target of 325 ± 25 µmol/L·h.
• Utilized a population pharmacokinetic model for retrospective analysis to improve AUC(CEPM) prediction.

Main Results:

• The mean adjusted second cyclophosphamide dose was 42 mg/kg, resulting in a mean total dose of 86 mg/kg (range: 54-120 mg/kg).
• The mean 0-48 hour AUC(CEPM) was 296 µmol/L·h (95% CI: 275-317 µmol/L·h), achieving the target metabolic endpoint.
• Retrospective analysis suggested population pharmacokinetic modeling could enhance AUC(CEPM) prediction accuracy.

Conclusions:

• Metabolism-based, dose-adjusted cyclophosphamide administration is feasible in HCT.
• Achieving a target AUC(CEPM) endpoint with adjusted dosing is possible.
• Lower cyclophosphamide doses guided by metabolism do not appear to compromise engraftment in HCT recipients.