Methadone Pharmacokinetics in Cardiac Surgery

The uncertainty regarding optimal methadone dosing and the necessity of post-cardiopulmonary bypass (CPB) supplementation provides a compelling rationale for this study. Specifically, it remains unknown whether a single higher initial dose of methadone can adequately maintain analgesic plasma concentrations throughout cardiac surgery and recovery, or if a split-dosing strategy administering a lower initial dose followed by an additional dose post-CPB might offer similar or improved analgesic outcomes with fewer side effects. This study will evaluate pharmacokinetics of methadone using three different dosing strategies in patients undergoing cardiac surgery with CPB.

Inclusion criteria

• Elective cardiac surgery requiring median sternotomy and cardiopulmonary bypass (CABG, valve, combined CABG/valve surgeries)
• Anticipated extubation within 12 hours postoperatively
• No prior opioid use within 30 days of surgery
• Ability to provide informed consent

Exclusion criteria

• Severe liver or kidney dysfunction (Child-Pugh class B/C, eGFR <30 mL/min/1.73m², creatinine >2 mg/dL, dialysis)
• Allergy to methadone or fentanyl
• Use of CYP3A4 inducers (rifampin, phenytoin, carbamazepine), CYP3A4 inhibitors (ketoconazole, erythromycin, clarithromycin, itraconazole), SSRIs (fluoxetine, sertraline, paroxetine, citalopram, escitalopram, fluvoxamine)
• Body mass index >40 kg/m²
• Corrected QT interval interval >500 milliseconds
• Intubation anticipated >12 hours
• History of illicit drug use or alcohol or opioid abuse use disorder within last 12 months
• Mechanical circulatory support, heart transplant, deep hypothermic circulatory arrest procedures
• Left Ventricular Ejection Fraction <30%
• Pulmonary disease requiring oxygen therapy
• Preoperative inotropic support or intra-aortic balloon pump
• Emergency surgery
• Postoperative regional anesthesia
• Hemofiltration during cardiopulmonary bypass