Pharmacokinetics of Rectal Drug Administration, Part II

Abstract

Part I of this article, which appeared in the previous issue of the Journal, covered general considerations, the physiology of the rectum, spreading of drugs into the colon, rectal absorption, partial avoidance of first-pass elimination, rate-controlled rectal delivery of drugs, irritation of the rectal mucosa and clinical applications of rectal administration, and discussed centrally acting drugs. In Part II, this discussion is extended to drugs which act peripherally and to methods of enhancing rectal drug absorption. The overall summary appeared in Part I.

Symptom control in cancer patients: the clinical pharmacology and therapeutic role of suppositories and rectal suspensions

“…Absorption from suppositories does depend upon a small particle size of drug [92,174]. Suspensions of <20 ml are more readily absorbed than suppositories [39,174].…”

“…Absorption from suppositories does depend upon a small particle size of drug [92,174]. Suspensions of <20 ml are more readily absorbed than suppositories [39,174]. Rectal bioavailability of 1 g acetaminophen given in a 20-ml suspension is 90-91% relative to the same dose given orally (relative bioavailability) [174].…”

“…Suspensions of <20 ml are more readily absorbed than suppositories [39,174]. Rectal bioavailability of 1 g acetaminophen given in a 20-ml suspension is 90-91% relative to the same dose given orally (relative bioavailability) [174]. Bioavailability from a fatty base and a PEG solution are the same as oral, but the time to maximum concentration (T-max) is delayed by rectal dosing (1.6 h versus 0.6 h) [174].…”

“…Rectal bioavailability of 1 g acetaminophen given in a 20-ml suspension is 90-91% relative to the same dose given orally (relative bioavailability) [174]. Bioavailability from a fatty base and a PEG solution are the same as oral, but the time to maximum concentration (T-max) is delayed by rectal dosing (1.6 h versus 0.6 h) [174]. Absorption is faster from a fatty than from a hydrophilic base suppository, though this is probably not clinically important [174].…”

“…Bioavailability from a fatty base and a PEG solution are the same as oral, but the time to maximum concentration (T-max) is delayed by rectal dosing (1.6 h versus 0.6 h) [174]. Absorption is faster from a fatty than from a hydrophilic base suppository, though this is probably not clinically important [174]. The higher the monoglyceride content of the Witepsol base (W35>H15), the better the absorption [30] (Tables 2, 3).…”