Table 3.
Comparison of warfarin dosing models in African Americans
| Model | Entry into model | Variable | Gene | Univariate r2 | Adjusted R2 after entry |
P |
|---|---|---|---|---|---|---|
| IWPC model | 1 | Age in decades | NA | — | 14.7 | 5.31 E-13 |
| 2 | Height (cm) | NA | 4.5 | 15.4 | 0.00298 | |
| 3 | Weight (kg) | NA | 9.0 | 17.6 | 0.0034 | |
| 4 | VKORC1-1639 | VKORC1 | 9.1 | 23.3 | 4.86 E-6 | |
| 5 | CYP2C9 *2 (rs1799853) | CYP2C9 | 1.3 | 24.9 | 0.047 | |
| 6 | CYP2C9 *3 (rs1057910) | CYP2C9 | 1.6 | 25.3 | 0.11 | |
| 7 | Race | NA | ND | ND | ND | |
| 8 | Enzyme inducer status | NA | 2.0 | 25.6 | 0.18 | |
| 9 | Amiodarone status | NA | 0.003 | 25.8 | 0.24 | |
| African-American model | 1 | Age in years | NA | — | 14.7 | 5.31 E-13 |
| 2 | Weight (kg) | NA | 9.0 | 20.5 | 2.84 E-6 | |
| 3 | DVT/PE | NA | 4.1 | 22.0 | 0.00747 | |
| 4 | VKORC1 1173 | VKORC1 | 9.9 | 29.4 | 1.40 E-8 | |
| 5 | CYP2C9 star alleles | CYP2C9 | 5.6 | 37.1 | 1.84e-07 | |
| 6 | VKORC1-8191 (rs61162043) | VKORC1 | 3.2 | 38.6 | 0.00413 | |
| 7 | 18786 (rs7089580) | CYP2C9 | 0.4 | 40.0 | 0.0346 |
Both univariate and multivariate coefficients are expressed in term of percentage. Multivariate R2 and P value were calculated in our combined data set using the variables published in the IWPC study.14 Race was not considered since all subjects were African American. Enzyme inducer status = 2 if patient is taking carbamazepine, phenytoin, rifampin or rifampicin, otherwise 1. Amiodarone status = 2 if patient is taking amiodarone, otherwise 1. DVT/PE = 2 if the indication for warfarin use is deep-vein thrombosis and/ or pulmonary embolism, otherwise 1. CYP2C9 star allele = 2 the presence of any of the following alleles: CYP2C9*2, *3, *5, *8, or *11, otherwise 1. P values presented in the table are associated with the variable upon entry into the model.
CYP2C9, cytochrome P-450 2C9; IWPC, International Warfarin Pharmacogenetic Consortium; NA, not applicable; ND, not determined.