Oral versus rectal ibuprofen in healthy volunteers

Ibuprofen is a safe and effective non steroidal anti-inflammatory drug (NSAID). Ibuprofen suppositories are marketed in Europe; but data regarding pharmacokinetics of rectal vs. oral ibuprofen in humans is scarce. The objective of this study is to compare the pharmacokinetics of single-dose rectal vs. oral ibuprofen in healthy adult volunteers.

Ten healthy adult male volunteers, aged 20-37 years, received in a non-blind, cross-over setting, two formulations of ibuprofen. First, a 400 mg (about 5 mg/kg) of racemic ibuprofen suppository; second (after a three week washout period) the same dosage of ibuprofen syrup. Blood samples were collected before dosing and for 12 hours after administration. Pharmacokinetics analysis was preformed.

Mean peak plasma concentration (Cmax) of rectal ibuprofen was considerably lower, and the mean time to peak (Tmax) considerably longer, compared to oral ibuprofen. Absorption of rectal ibuprofen was considerably lower than oral ibuprofen, with a relative bioequivalence of 63%. Rectal ibuprofen reached therapeutic plasma concentration (>10 µg/ml) 45 minutes after dosing and remained in that range for four hours. The values of Vd/F and CL/F also differ significantly after rectal and oral administration, while no difference was found in the elimination rate constant (Kel) or half-life elimination (t1/2).

Racemic ibuprofen suppository has lower bioavailability compared with ibuprofen syrup. Therapeutic plasma concentrations of ibuprofen were reached 45 minutes after dosing and remained in that range for 4 hours. Ibuprofen suppositories can contribute to the management of fever and pain when the oral route is not available.