The irritative effects of 10% phenobarbital (PH) and phenobarbital sodium (PHS) solution for injection, 5% pentobarbital sodium (PES) solution for injection, 10% thiopental sodium (THS) solution for injection, and 5% chloral hydrate (CHH) solution on the rectal membranes of rabbits were examined wit h and without optical and scanning electron microscopes. Little irritation was observed after administration of PHS, THS, and CHH. However, PH and PES caused severe and mild irritation on the rectal membranes after rectal administration, respectively. Irritative effects of PH and PES may be attributed to organic solvents contained in these compounds
