Bioavailability of indomethacin after intramuscular injection and rectal administration of solution and suppositories

The pharmacokinetics of indomethacin was studied after intravenous and intramuscular injection of 50 mg and administration of rectal solution and suppositories of 100 mg to 8 volunteers. Peak plasma concentrations of indomethacin occurred 20 min. after administration of the rectal solution (3.7 micrograms X ml-1), 40 min. after intramuscular injection (2.7 micrograms X ml-1), and 60 min. after suppositories (3.7 micrograms X ml-1). The bioavailability after the two rectal forms was found to be almost the same, about 80%. After intramuscular injection the bioavailability was calculated to be complete. These results suggest that indomethacin administered as a rectal solution or as intramuscular injection may be an alternative to intravenous administration when an early plasma peak of the drug is required.