Disposition of chloramphenicol in low birth weight infants.

Although infrequently an antibiotic of first choice for neonates, chloramphenicol (CL) may be indicated in selected instances of infection caused by aminoglycoside-resistant enterobacteriaciae, anaerobes, and ampicillin-resistant Haemophilus influenzae. Use of CL in neonates has been limited since the recognition that vascular collapse may occur as a consequence of dosage regimens tolerated by adults. With an assay that detects only active CL, we studied drug disposition in 13 low birth weight infants, eight between 1 and 8 days of age (group I), and five between 11 days and 8 weeks of age (group II). Peak serum CL concentrations ranged from 11.2 to 36.2 microgram/ml in group I and from 10.0 to 36.2 microgram/ml in group II, at doses ranging from 15 to 50 mg/kg/day, and 25 to 50 mg/kg/day, in groups I and II, respectively. Serum CL half-lives (T1/2) ranged from 10 to 36 hours in four of the eight group I patients; three of the remaining patients had T1/2 greater than 48 hours and the fourth patient accumulated CL in the interval between doses. T1/2 in group II ranged from 5.5 to 15.7 hours. Observed differences in T1/2 between groups I and II were statistically significant (P = .05) and could not be accounted for by factors other than postnatal age. These preliminary data suggest that although there appears to be an inverse relationship between CL T1/2 and postnatal age, there is sufficient variability in serum levels that monitoring must be performed in low birth weight infants treated with this drug.