Posted by Cam W. on July 31, 2002, at 20:12:51
In reply to Prozac, Codeine, cyp2d6..CamW or anyone ?, posted by janejj on July 31, 2002, at 14:04:39
Jane - I was at a presentation about 5 years ago where the presenter had mentioned that Paxil (paroxetine), and to a lesser extent Prozac (fluoxetine) inhibited the conversion of codeine to morphine (the active metabolite of codeine - ie. codeine's main active constituent).
I have heard this interaction sporatically, butI have seen no hard evidence. Paxil's monograph used to contain a blurb on the inhibiton of the conversion, butI looked tonight and it's no longer there.
Codeine is not metabolized to any major extent by CYP-2D6, but is at least partially metabolized by one of those lesser known and weirder cytochrome enzymes. If memory serves me correctly, it is CYP-2C17 (or something like that). The CPS says that codeine's main excretable metabolite is glucuronide-conjugated morphine, and glucuronide-conjugation is done mainly by the cytochrome system, is also done in the blood stream.
So, is the Prozac/Paxil-codeine interaction a myth? I don't know. It seems to have all the ingredients of an urban legend (eg. [1] "a friend of a friend told me that the pain in his hip (back, knee - mostly likely = neck) came back when he started Prozac; [2] the story is believable enough that it "might" be true .... [3] the story changes to fit the times: Prozac was released first, thus the story began with it; the Paxil became the new wonder drug, so the story changed to reflect this.
It might have been a disgruntled competing drug rep &/or former employee that started this urban legend (urban legend sound so much better than rumor).
An explanation that I came to while typing this post is that the list of start-up side effects, as well as withdrawl symptoms, include various types of pain: flu-like symptoms, abdominal pain, myalgia, limp willy (oh, sorry .... that's just a pain in the ass), back pain, itching, etc. Also, other start-up side effects include anxiety and nervousness. Combine this with the pain and depression, of course you codeine isn't going to work any more.
The preceding is just a guess on my part, but like an urban legend, it sounds good.
;^)
- Cam
poster:Cam W.
thread:114651
URL: http://www.dr-bob.org/babble/20020731/msgs/114701.html