Vancomycin pharmacokinetics were studied in nine premature infants. Infants weighing less than 1,000 gm had significantly larger volumes of drug distribution and consequently longer drug half-lives than larger premature infants, regardless of postconceptual or actual age. These differences alter the vancomycin dosing recommendations in these two groups of premature infants. We recommend initial ... [Show full abstract] dosage regimens consisting of a loading dose of vancomycin of 25 mg/kg followed by doses of 15 mg/kg every 12 hours for infants with weights less than 1,000 gm. Infants weighing over 1,000 gm should receive 10 mg/kg every 12 hours, with a loading dose of 12.5 mg/kg. Serum vancomycin concentration should be monitored, however, for final optimization of therapy.