Dear Drugs-Forum readers: We are a small non-profit that runs one of the most read drug information & addiction help websites in the world. We serve over 3 million readers per month, and have costs like all popular websites: servers, hosting, licenses and software. To protect our independence we do not run ads. We take no government funds. We run on donations which average $25. If everyone reading this would donate $5 then this fund raiser would be done in an hour. If Drugs-Forum is useful to you, take one minute to keep it online another year by donating whatever you can today. Donations are currently not sufficient to pay our bills and keep the site up. Your help is most welcome. Thank you.
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
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.
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.
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.