Table 1.
Assignment of likely codeine metabolism phenotypes based on CYP2D6 diplotypes
| Likely phenotypea | Activity score | Genotypes | Examples of diplotypes |
|---|---|---|---|
| Ultrarapid metabolizer (∼1–2% of patients) | >2.0 | An individual carrying more than two copies of functional alleles | *1/*1xN, *1/*2xN |
| Extensive metabolizer (∼77–92% of patients) | 1.0–2.0b | An individual carrying two alleles encoding full or reduced function or one full function allele together with either one nonfunctional or one reduced-function allele | *1/*1, *1/*2, *2/*2, *1/*41,*1/*4,*2/*5, *10/*10 |
| Intermediate metabolizer (∼2–11% of patients) | 0.5b | An individual carrying one reduced and one nonfunctional allele | *4/*10, *5/*41 |
| Poor metabolizer (∼5–10% of patients) | 0 | An individual carrying no functional alleles | *4/*4, *4/*5, *5/*5, *4/*6 |
a
The frequency estimates are based on data from Caucasians and may differ substantially for other ethnicities. See Supplementary Data online for estimates of phenotype frequencies among different ethnic/geographic groups.
b
Note that some investigators define patients with an activity score of 0.5 and 1.0 as intermediate metabolizers and define patients with an activity score of 1.5 and 2.0 as extensive metabolizers. Classifying patients with an activity score of 1.0 as extensive metabolizers in this guideline is based on data specific for formation of morphine from codeine in these patients.13