Ctc. Randall et Se. Tett, PHENYTOIN PHARMACOKINETICS AFTER INTRAVENOUS ADMINISTRATION TO PATIENTS RECEIVING ENTERAL TUBE-FEEDING, Pharmacy world & science, 16(5), 1994, pp. 217-224
Serial plasma samples were collected after administration of 13 intrav
enous dose of phenytoin to 11 patients with head injury; 5 to patients
who had been receiving enteral feeds for less than 5 days (group 1),
and 8 to patients who had been receiving enteral feeds for loner than
5 days (group 2). Average plasma phenytoin concentrations were higher
in group 1 than in group 2 (0.003). The median intravenous study dose
was the same (300 mg) in both groups (p=0.17). Group 2 received slight
ly higher doses expressed as mg/kg (median of 5.45 mg/kg compared to 4
.29 mg/kg in group 1, p=0.21). Phenytoin was more rapidly eliminated f
ollowing intravenous dosing patients receiving long-term enteral feedi
ng. V-max was higher in group 2 than in group 1 (medians, 709 versus 3
94 mg/day) and K-m smaller (medians, 2.5 versus 3.9 mg/l), but volume
of distribution was similar in both groups (p=0.88). The kinetic param
eters of phenytoin in group 1 were similar to previously published pop
ulation pharmacokinetic parameters. In order to maintain phenytoin con
centrations adequate for seizure prophylaxis in patients receiving lon
g-term enteral feeding it would be advisable to decrease the dosing in
terval as well as increasing the phenytoin dose when the drug is admin
istered intravenously.