Perioperative pharmacokinetics of ibuprofen enantiomers after rectal administration

Ibuprofen is a nonsteroidal anti-inflammatory drug which has both peripheral and central analgesic effects. Ibuprofen has been shown to be an effective antipyretic and postoperative analgesic drug both in adults and children with few side effects. Pharmacokinetics of rectal ibuprofen has not been studied, although suppositories are frequently used for perioperative pain control in children.

There were four study groups: full-term infants aged 1-7 weeks (n = 9), infants aged 8-25 weeks (n = 8), and infants aged 26-52 weeks (n = 7). Adult patients were 20-40 years old (n = 7). Ibuprofen suppository 20 mg.kg(-1) was administered after induction of anesthesia. Blood samples were collected from 20 min to 10 h after dosing and pharmacokinetic analysis of ibuprofen enantiomers were done.

Both ibuprofen enantiomers were detectable in blood in 20 min. Total ibuprofen plasma concentrations >10 mg.l(-1) were seen from 40 min to 8 h. Values for T(max) of ibuprofen enantiomers and total ibuprofen were higher in the adult group than any of the infant groups (P < 0.05). In addition, values for physiological (standardized) t(1/2) of (R)-(-)- and (S)-(+)-ibuprofen were higher in infants aged 1-7 weeks than the adults (P < 0.05). None of the other pharmacokinetic variables, C(max), AUC, chronological t(1/2) or AUC ratio differed between the groups.

A single dose of ibuprofen suppository 20 mg.kg(-1) after induction of anesthesia guarantees analgesic plasma concentrations during the early postoperative period. Except for the delayed absorption of ibuprofen in adults and higher physiological t(1/2) in infants aged 1-7 weeks, no major pharmacokinetic differences were observed between study groups.