Pharmacokinetics of chloramphenicol in the neonatal horse.

Chloramphenicol sodium succinate was administered as an intravenous bolus (50 mg/kg) to eight foals which weighed 49-57 kg (mean +/- 1 standard deviation = 53.19 +/- 2.66) each, and were 1-9 days (4.5 +/- 2.56) of age. The drug was rapidly distributed and followed first-order elimination. Mean pharmacokinetic values were: zero-time serum concentration (C0) = 36.14 microgram/ml (+/- 14.80); apparent specific volume of distribution (Vd) = 1.614 1/kg (+/- 0.669); and elimination rate constant (K) = 0.7295 h-1 (+/- 0.3066) which corresponds to a biological half-life (t1/2) = 0.95 h. These values do not differ greatly from those reported for adult horses and ponies. A suspension of chloramphenicol was administered by nasogastric tube (50 mg/kg) to a second group of seven foals which weighed 49 to 57 kg (51.34 +/- 2.82) each and were 1 to 7 days (4.43 +/- 1.90) of age. A mean peak serum chloramphenicol concentration of 23.97 microgram/ml (+/- 7.06) was achieved 1.14 h (+/- 0.63) after administration. The bioavailability of this preparation was 83.27 percent.