Question

33. A patient homozygous for CYP2D6 allele variants, that confer the poor metabolizer phenotype, has been treated with codeine. The treatment will result in:

A. Higher incidence of respiratory depression

B.High concentration of the codeine active metabolite

C. Low plasma concentration of codeine

D. Lack of analgesia

Answer 1

Answer- D- lack of analgesia.

Codeine belongs to the class of opioid analgesics and is used to relief mild to moderate pain sensations.

Normal CYP2D6 gene regulates the conversion of codeine to morphine which provides the pain relieving effect (analgesic effect)

However, individuals carrying two inactive copies of CYP2D6 gene (poor metabolizers) are not able to convert codeine effectively resulting in inadequate pain relief (lack of analgesia) due to decreased levels of morphine.

Individuals with poor metabolizer phenotype are recommended to avoid codein due to lack of analgesia. In this case, opioids not metabolized by CYP2D6 can be more effective than codeine.