Bradycardia during methadone therapy in an infant

To report the occurrence of bradycardia associated with the use of methadone administered to prevent withdrawal in an infant with physical tolerance following long-term opioid therapy in the pediatric intensive care unit setting.

Retrospective case report.

Methadone (0.1 mg/kg) was administered to a 6-month-old infant following prolonged use of intravenous fentanyl for sedation during respiratory failure requiring mechanical ventilation. Approximately 30-60 mins after the first dosing of methadone, the infant's heart rate decreased from his baseline of 130-140 beats/min to 80-90 beats/min for 30 seconds. After the third dose of methadone, the heart rate decreased to a sinus bradycardia of 60-70 beats/min for 4 mins. The episodes resolved with tactile stimulation. Over the next 18 hrs, there were repeated episodes of bradycardia. None of these episodes were associated with hypotension, apnea, change in oxygen saturation, decreased peripheral perfusion, or other signs of hemodynamic instability. The methadone was withdrawn and the intravenous fentanyl infusion was restarted. Eight to 10 hrs after administration of the last dose of methadone, the episodes of bradycardia resolved and the patient remained in a normal sinus rhythm with a heart rate of 120-140 beats/min.

Methadone's three-dimensional structure shares similarities with calcium channel antagonists. Although it has been reported in the adult literature, there are no previous reports of bradycardia occurring with methadone therapy in infants. Although there were no deleterious physiologic effects related to the bradycardia in our patient, methadone should be used cautiously in patients who may not tolerate alterations in heart rate.