In the preliminary group of premature infants, those receiving q 6h dosing had an average trough concentration of 7.3 uM (18%). However, the premature infants in the preliminary pharmacokinetic study did not have long term follow-up to assess toxicity. Due to the potential for altered ZDV pharmacokinetics and increased toxicity in this population, an evaluation of ZDV pharmacokinetics in premature infants is proposed.