First‐pass elimination of salicylamide in man following oral and rectal administration

In order to study the avoidance of hepatic first-pass elimination following rectal administration, 500 mg of salicylamide (SAM) were given orally and rectally to man. Plasma SAM concentrations were measurable following oral administration, but following rectal administration SAM concentrations were either very low or not detectable. The mean excretion of SAM sulphate (SAMS) and SAM glucuronide (SAMG) in the urine following oral and rectal administration was 71.3 per cent and 45.6 per cent respectively. Increasing the oral and rectal dose (1500 mg of SAM, solution) showed that the mean AUC values were 911 and 144 micrograms min ml-1, respectively. The mean urinary excretion of SAMS plus SAMG following oral and rectal administration was 82.0 and 75.6 per cent respectively; the mean plasma elimination half-lives were 31 and 40 min, respectively, while the mean urinary elimination half-lives were 63 and 73 min, respectively.