Palivizumab use in very premature infants in the neonatal intensive care unit

Objective. The purpose of this study was to determine the ability of young hospitalized premature (born less than or equal to30 weeks' gestational age) infants to achieve serum levels of palivizumab that are protective against RSV infection. Methods. Palivizumab, 15 mg/kg per dose intramuscularly, was administered every 28 days to stable premature infants who were hospitalized in the neonatal intensive care unit starting at 1 month of postnatal life. Palivizumab concentrations were assayed in serum samples that were drawn from infants who remained in the hospital at 14 days (midpoint concentration) and at 28 days ( trough concentration) after each dose was administered. Results. The gestational age of the 24 infants who were enrolled was 27.5 +/- 1.8 weeks (mean +/- standard deviation), and birth weight was 928 +/- 159 g. Midpoint palivizumab concentrations in the 24 infants after the first dose were 45.6 +/- 13.0 mug/mL; 71% (17 of 24) of the infants maintained optimal palivizumab concentrations (greater than or equal to40 mug/mL). The concentrations dropped subsequently; trough concentrations just before the second dose were 32.2 +/- 10.5 mug/mL, and only 23% (5 of 22) of the infants had concentrations in the optimal range. Sixteen infants were given 2 doses and 6 were given three doses of palivizumab while in the neonatal intensive care unit. Midpoint concentrations after the second dose were significantly higher than those after the first dose. Likewise, trough concentrations before the third dose were 51.9 +/- 7.8 mug/mL and higher than those before the second dose; the concentrations were greater than or equal to40 mug/ml in all 6 infants tested. Conclusions. Very premature infants had sustained optimal protective serum concentrations only after the second dose of palivizumab; 77% of infants tested had trough concentrations <40 mu g/mL before the second dose. Additional studies are needed to establish the optimal timing of the initial dose and optimal dosing interval of palivizumab in this most vulnerable population.