Dose-response relationship of doxapram in the therapy for refractory idiopathic apnea of prematurity.

Eighteen infants with idiopathic apnea of prematurity refractory to therapeutic levels of aminophylline were treated with incremental doses of doxapram beginning at 0.5 mg/kg/h. Continuous recording of heart rate, thoracic impedance, and transcutaneous PO2 demonstrated that 47% of the infants satisfied objective response criteria at the lowest dose, 53% responded at 1.0 mg/kg/h, 65% at 1.5 mg/kg/h, 82% at 2.0 mg/kg/h, and 89% at the highest allowed dose of 2.5 mg/kg/h. The mean serum doxapram concentration at the response dose was 2.9 +/- 1.3 micrograms/mL, and all infants who responded had levels greater than 1.5 micrograms/mL. BP was significantly elevated at doses higher than 1.5 mg/kg/h (P less than .05). Minute ventilation significantly increased and PCO2 significantly decreased as the doxapram dosage was increased (P = .02). Terminal elimination half-life was 9.9 +/- 2.9 hours. When doxapram is used for treatment of refractory neonatal apnea the starting dosage should be no more than 0.5 mg/kg/h.