Least analgesic response following the administration of codine

Discussion in 'MRCPsych Forum' started by manjeet, May 20, 2011.

  1. manjeet

    manjeet Guest

    Which group would be expected to display the least analgesic response following the administration of codine

    A. Black

    B. Hispanic

    C. American Indian

    D. Caucasian

    E. Asian
  2. manjeet

    manjeet Guest

    Ans Caucasion
    Codeine is routinely converted to morphine in the body in order for it to be an effective painkiller. The metabolism of codeine to morphine takes place in the liver through the actions of an enzyme called CYP2D6. Most people have normal CYP2D6 activity and their response to codeine is as expected. However, a substantial minority of people— differing by national origin and race (see below)—have CYP2D6 activity that is higher or lower than normal, potentially resulting in excessive (higher activity) or inadequate (lower activity) response to codeine.

    The effect of genetics on the CYP2D6 enzyme has been extensively studied, and we now know that total CYP2D6 deficiency occurs in about 6 to 10 percent of Caucasians, 3 to 6 percent of Mexican Americans, 2 to 5 percent of African Americans and about 1 percent of Asians Americans.
    CYP2D6 is important as it exhibits genetic polymorphism (it varies in its expression from person to person). Caucasians show less activity of CYP2D6 than their Asian and Black counterparts. This is also important when the effect of a drug relies on an active metabolite as in the case of codeine. CYP2D6 is not really involved in induction interactions but is inhibited by SSRI’s particularly paroxetine.

    The CYP3A subfamily is the most abundant. They are most commonly involved in interactions involving induction and inhibition. Grapefruit juice specifically inhibits CYP 3A4. Drugs metabolised by this enzyme include; carbamazepine, diazepam, sertraline, buspirone. Grapefruit juice also inhibits CYP 1A2 causing an increase in clozapine levels. Smoking causes induction of CYP 1A2.

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