Pharmacokinetics of Intravenous and Rectal Ketoprofen in Young Children

Objective: To evaluate the relative bioavailabilities of ketoprofen after intravenous and rectal administration to young children.

Design: Open-label prospective parallel-group study.

Patients: Participants were 28 children aged 7 to 93 months.

Methods: Eighteen children received a single intravenous injection of ketoprofen 1 mg/kg, and ten children, weight 16–24 kg, received a 25mg ketoprofen suppository. Venous blood samples were collected at selected times after administration, ranging from 2 minutes to 8 hours for the intravenous group and from 30 minutes to 8 hours for the suppository group. A validated high performance liquid chromatography method was used to measure plasma ketoprofen concentrations.

Results: In the intravenous group, the maximum plasma concentration of ketoprofen ranged between 10.5 and 22.2 mg/L, and in the suppository group, following dose normalisation to 1 mg/kg of ketoprofen, between 3.8 and 7.4 mg/L. In the intravenous group, area under the concentration-time curve from zero to infinity ranged between 9.2 and 23.5 mg · h/L, and in the suppository group after dose normalisation between 8.8 and 12.9 mg · h/L. The bioavailability of ketoprofen from the suppository was about 73%. Volume of distribution was 0.04–0.10 L/kg in the intravenous group and 0.08–0.16 L/kg in the suppository group. The terminal half-life was comparable in both study groups, ranging between 0.7 and 3.0 hours in the intravenous group and between 1.2 and 2.9 hours in the suppository group.

Conclusion: Absorption of ketoprofen after rectal administration is reasonably rapid and predictable. Because the bioavailability of rectal ketoprofen is also relatively high, a suppository may be used in children in whom the drug cannot be given intravenously or by mouth.