Observations on the urine metabolic profile of codeine in pain patients.

This retrospective data analysis explored the relationship between codeine and its metabolites morphine, hydrocodone and hydromorphone. The objectives were: (i) to determine urine concentrations and mole fractions of codeine and metabolites and (ii) to examine the effect of cytochrome P450 (CYP) 2D6 inhibition on metabolite mole fractions. De-identified urine specimens were collected between September 2010 and July 2011 and analyzed using LC-MS-MS to determine codeine, morphine, hydrocodone and hydromorphone concentrations. Geometric mean urine concentrations were 0.833, 0.085 and 0.055 for morphine, hydrocodone and hydromorphone, respectively. Mole fractions were 0.23, 0.025 and 0.014 for morphine, hydrocodone and hydromorphone, respectively. The fraction of excreted codeine in the urine increased (slope = 0.06 ± .01, R² = 0.02) with total moles. As the total amount of codeine and metabolites increased, the fraction of codeine increased, while the fraction of active metabolites decreased. CYP2D6 inhibition with paroxetine, fluoxetine, bupropion and methadone significantly decreased the fraction of morphine excreted. The prevalence of codeine metabolism to morphine was considerably higher than codeine to hydrocodone. The urine concentration of codeine excreted was the greatest, followed by morphine and hydrocodone. Subjects should be monitored during concomitant use of codeine and CYP2D6 inhibitors as this affects the amount of morphine metabolite formation.