Bioavailability of acetaminophen suppositories.

Urinary excretion of acetaminophen after rectal administration of three suppository formatulations obtained from hospital and commercial sources was compared to that after oral administration of a tablet dosage form. The absorption of acetaminophen from the suppositories was extremely variable and showed relative bioavailabilities of 68.4 to 87.5% when compared to the oral absorption of the drug from the tablet. The rate of bioavailability differed markedly between products and, in one case, the suppository dose of acetaminophen was so slowly absorbed that the clinical effectiveness of the product is doubtful. The study points out the need for in vivo evaluation of hospital pharmacy manufactured products.