Pharmacokinetics of doxapram were determined in 13 infants with idiopathic apnea of prematurity uncontrolled by aminophylline and caffeine. Doxapram was maintained for 72-96 h at a constant infusion rate of 2-2.5 mg/kg/h. Plasma doxapram levels were measured by gas liquid chromatography. The infants studied had a birth weight of 1,247 ± 240 g (mean ± SD), a gestational age of 29.4 ± 2 weeks and were 9.9 ± 6 days old. Steady-state plasma doxapram levels reached by all infants averaged 5.8 ± 1.8 mg/l. Half-life was 6.6 ± 5.7 h, plasma clearance 0.44 ± 0.1 litres/kg/h, and calculated volume of distribution 4 ± 2.7 litres/kg. Doxapram controlled apnea successfully in 12 of 13 babies. A significant fall in PaCO(2) and reduction in the rate of apnea was seen within 6-8 h with corresponding doxapram levels of 3.7 ± 1.8 mg/l. The factors influencing the pharmacokinetics of doxapram in newborns are presently unknown.

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