Phase I evaluation of zidovudine administered to infants exposed at birth to the human immunodeficiency virus

This study evaluated the safety, tolerabillity, and pharmacokinetics of zidovudine administered intravenously and orally to infants born to women infected with the human immunodeficiency virus. Thirty-two symptom-free infants were enrolled before 3 months of age. The pharmacokinetics of zidovudine were evaluated in each infant after single intravenously and orally administered doses of zidovudine on consecutive days, and during long-term oral administration of the drug for 4 to 6 weeks. As new patients were enrolled, doses of zidovudine were progressively increased from 2 to 4 mg/kg. Therapy was continued for up to 12 months in 7 of the infants proved to be infected with human immunodeficiency virus. Zidovudine was generally well tolerated; 20 children (62.5%) had anemia (hemoglobin level <10.0 gm/dl) during therapy and 9 (28.1%) had neutropenia (neutrophil count ≤750 cells/mm³); these hematologic abnormalities usually resolved spontaneously. The total body clearance of zidovudine increased significantly with age, from an average of 10.9 ml/min per kilogram in infants ≤14 days of age to 19.0 ml/min per kilogram in older infants (p<0.0001). Concurrently, there was a significant decrease in serum half-life from 3.12 hours in infants ≤14 days to 1.87 hours in older infants (p=0.0002). Oral absorption was satisfactory and bioavallability decreased significantly with age, from 89% in infants ≤14 days to 61% in those >14 days of age (p=0.0002). Plasma concentrations of zidovudine were calculated to be in excess of 1 μmol/L(0.267 μg/ml) for 4.12±1.86 hours and 2.25±0.78 hours after oral doses of 2 mg/kg in infants younger than 2 weeks and 3 mg/kg in older infants, respectively. We conclude that zidovudine administered at oral doses of 2 mg/kg every 6 hours to infants aged less than 2 weeks and 3 mg/kg every 6 hours to infants older than 2 weeks resulted in plasma concentrations that are considered virustatic against human immunodeficiency virus. Zidovudine was well tolerated by infants at these doses.