Pharmacokinetic analysis of cefmenoxime (CMX) was carried out in preterm and terminfants after single intravenous administration.
The mean elimination half-life (t1/2) value of CMX in four infants ranging in the agesfrom 6months to 2yr was calculated to be 0.83±0.06 (mean±SE) hr, which was similarto a reported value in adults. The mean t1/2value in neonates, including preterm infants (postnatal age1.7±1.2day, birth welght 2, 426±242g), was 6.2±1.0 (mean±SE) hr, whichwas markedly longer than that in older infants. Total body clearance (Cltot) of CMX inneonates was reduced to 22.8±3.6 (mean±SE) ml/min/1.73m2, which was less than onetenth of the Clot value of CMX in older infants. Apparent volumes of distribution werenot significantly different (P>0.05) among age groups.
We found that decrease in post-conceptional age tended to prolong t1/2 and reduce Cltot.Clearance ratio (CR) of renal clearance of CMX to its glomerular filtration rate (GFR) wasalso calculated by measuring the drug in urine to evaluate the effect of tubular secretionof CMX by co-administration of probenecid. CR of CMX with co-administration of probenecid was reduced compared to that without probenecid in a healthy volunteer. It wasrecognized that a short postconceptional age tended to reduce CR of CMX. The decreasein glomerular filtration and tubular secretion function in neonates including prematureinfants is likely to cause a remarkable prolongation of a t1/2 value of CMX. Thus, weconclude that adjustment of the dosing schedule of CMX in neonates in age of less than7 days will be required.
