[Drug administration through the rectum: reliability, tolerance]

The main form of rectal administration of medications is the suppository. The rapidity of release of the active principle in the rectal fluid depends mainly on the physicochemical properties of the vehicle. Absorption per se is influenced by the liposolubility as well as the ionization of the medication, and by the site of its release since only the middle and inferior hemorrhoidal veins avoid the hepatic crossing. For molecules subjected to a major 1st hepatic crossing (lidocaine, propranolol, ergotamine...), pharmacokinetic studies demonstrate that the rectal route enables to obtain a bioavailability which is markedly higher by oral route, and plasma concentrations at a therapeutic level. The use, still experimental, of rectal osmotic pumps, provides balanced plasma concentrations which remain stable during the entire duration of the application. Undesirable side effects related to the administration of drugs via the rectal route, are, most of the time, local ones. The vehicles seem to be responsible for diffuse ano-rectitis. Cases of rectal ulcerations with necrosis have been reported following the excessive use of suppositories containing dextro-propoxyphene or ergotamine.