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Old 22-06-2013, 17:40
fleeman fleeman is offline
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How much Codeine metabolizes into Morpine?

Hey first post here.

I have looked up and down this forum for an answer but couldn't find anything.

A Buddy of mine was wondering how much codeine actually metabolizes into Morphine?

For example if he were to take 50mg of codeine, how much of that would metabolize into morphine?

thanks in advance for any replies!
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Old 22-06-2013, 18:18
Millie Platt Millie Platt is offline
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Re: How much Codeine metabolizes into Morpine?

i'm sure this has been covered about a million times but the rule of thumb is roughly 10% - give or take depending on metabolism.

some can't metabolise it at all.
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Old 22-06-2013, 20:53
Mindless Mindless is offline
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Re: How much Codeine metabolizes into Morpine?

The amount of codeine metabolised into morphine can vary. Some individuals appear to be extensive metabolisers, while others may be poor metabolisers. 6%-10% Caucasians, 2%-5% African Americans, and 1% Asians are poor metabolisers of CYP2D6 substrates such as codeine
Quote:
Patients who are CYP2D6 PMs (Poor Metabolisers) will not convert codeine to morphine and will have a reduced analgesic effect from codeine. When patients who are CYP2D6 EMs (Extensive Metabolisers) are administered a CYP2D6 inhibitor, they do not convert much codeine to morphine and have a minimal analgesic response to the codeine.
Ten percent seems to be the usual overall dose of morphine from codeine. Perhaps members of this group occupy points around the middle of a poor metaboliser-extensive metaboliser continuum.

Drug Interactions: insights and observations. Understanding an Important Variable in Patient Response. John R. Horn, PharmD, FCCP, and Philip D. Hansten, PharmD, Pharmacy Times 2006.

It has been suggested that extensive metabolisers may convert codeine into morphine at an 'ultra-rapid' rate. CYP3AF inhibitors and renal insufficiency may lead to an increased risk of codeine toxicity for extensive metabolisers.

Codeine Intoxication Associated With Ultrarapid CYP2D6 Metabolism.

Chen et al (1991) make similar comments:
Quote:
There are several potentially important clinical implications of our findings. In healthy young subjects, there is unlikely to be unpredictable accumulation of codeine and codeine-6-glucuronide with chronic administration. This may not be the case, however, in patients with impaired renal function and in the elderly, in whom plasma codeine-6-glucuronide concentrations may be substantial and could contribute to adverse effects. Poor metabolisers of codeine may not derive any of the pharmacological effects associated with codeine.
Disposition and metabolism of codeine after single and chronic doses in one poor and seven extensive metabolisers.

Post Quality Evaluations:
Interesting data on ethnic variables

Last edited by Mindless; 20-07-2013 at 13:42. Reason: corrected hyperlink

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