The area of the rectum that absorbs straight to the bloodstream is only about 6 centimeters, the majority, esp when laying on your side all goes through the hepatic portal vein, making the uptake and 1st pass metab. about the same as the stomach, minus all that extra surface area in the stomach.
Although there was a thread from NP&D lost in the prune that had data backing up a massive increase in rectal BA by deprotonation of the MS. It wasn't quite high enough to liberate it from it's salt and precipitate to base, but was close from what I hazily remember. If you come across anything like that Negrogesic, please let me know. Thx.
Also with Morphine being the main desired constituent of Poppies/ Opium/ tea, here's some articles on it.
Plasma concentrations of morphine were followed for 24 hours in eight patients after intravenous and rectal administration of 10 mg morphine chloride. The plasma levels of morphine were determined by a sensitive and specific radioimmunoassay based upon an extraction procedure which separates...
www.ncbi.nlm.nih.gov
https://bjanaesthesia.org/article/S0007-0912(17)42397-X/pdf
I guess you really have to be a stand-up Guy/Gal to bypass that hepatic portal.
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