The mechanism of action through which ibuprofen causes closure of a patent ductus arteriosus (PDA) in neonates is not known. In adults, ibuprofen is an inhibitor of prostaglandin synthesis.

The pharmacokinetic data were obtained from 54 NeoProfen-treated premature infants included in a double-blind, placebo-controlled, randomized, multicenter study. Infants were less than 30 weeks gestational age, weighed between 500 and 1000 g, and exhibited asymptomatic PDA with evidence of echocardiographic documentation of ductal shunting. Dosing was initially 10 mg/kg followed by 5 mg/kg at 24 and 48 hours.

The population average clearance and volume of distribution values of racemic ibuprofen for premature infants at birth were 3 mL/kg/h and 320 mL/kg, respectively. Clearance increased rapidly with post-natal age (an average increase of approximately 0.5 mL/kg/h per day). Inter-individual variability in clearance and volume of distribution were 55% and 14%, respectively. In general, the half-life in infants is more than 10 times longer than in adults.

The metabolism and excretion of ibuprofen in premature infants have not been studied.

In adults, renal elimination of unchanged ibuprofen accounts for only 10-15% of the dose. The excretion of ibuprofen and metabolites occurs rapidly in both urine and feces. Approximately 80% of the dose administered orally is recovered in urine as hydroxyl and carboxyl metabolites, respectively, as a mixture of conjugated and unconjugated forms. Ibuprofen is eliminated primarily by metabolism in the liver where CYP2C9 mediates the 2- and 3-hydroxylations of R- and S-ibuprofen. Ibuprofen and its metabolites are further conjugated to acyl glucuronides.

In neonates, renal function and the enzymes associated with drug metabolism are underdeveloped at birth and substantially increase in the days after birth.

In a double-blind, multicenter clinical study premature infants of birth weight between 500 and 1000 g, less than 30 weeks post-conceptional age, and with echocardiographic evidence of a PDA were randomized to placebo or NeoProfen. These infants were asymptomatic from their PDA at the time of enrollment. The primary efficacy parameter was the need for rescue therapy (indomethacin, open-label ibuprofen, or surgery) to treat a hemodynamically significant PDA by study day 14. An infant was rescued if there was clinical evidence of a hemodynamically significant PDA that was echocardiographically confirmed. A hemodynamically significant PDA was defined by three of the following five criteria bounding pulse, hyperdynamic precordium, pulmonary edema, increased cardiac silhouette, or systolic murmur or hemodynamically significant ductus as determined by a neonatologist.

One hundred and thirty-six premature infants received either placebo or NeoProfen (10 mg/kg on the first dose and 5 mg/kg at 24 and 48 hours). Mean birth age was 1.5 days (range: 4.6 - 73.0 hours), mean gestational age was 26 weeks (range: 23 - 30 weeks), and mean weight was 798 g (range: 530 - 1015 g). All infants had a documented PDA with evidence of ductal shunting. As shown in Table 1, 25% of infants on NeoProfen required rescue therapy versus 48% of infants on placebo (p=0.003 from logistic regression controlling for site).

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