Table 5.
Unadjusted and adjusted hazard ratios for time to maintenance dose in subcohort with adherence data.
| Factora (N = 143)b | N (%) | N (%) Reaching Maintenance Dosec | Unadjustedd | Adjusted (− Adherence)d | Adjusted (+ Adherence)d,g | |||
|---|---|---|---|---|---|---|---|---|
| Hazard Ratioe | P-valuef | Hazard Ratioe | P-valuef | Hazard Ratioe | P-valuef | |||
| ≥ 80% adherenceh | — | — | 1.95 (1.06, 3.59) | 0.032* | — | — | 1.70 (0.88, 3.27) | 0.11 |
| Race | ||||||||
| African American | 60 (42) | 39 (65) | 0.88 (0.54, 1.43) | 0.60 | 0.84 (0.44, 1.61) | 0.61 | 0.90 (0.46, 1.76) | 0.77 |
| Caucasian or other | 83 (58) | 57 (69) | — | — | — | |||
| Previous use of warfarin | ||||||||
| Yes | 38 (27) | 26 (68) | 0.67 (0.41, 1.11) | 0.12 | 0.58 (0.32, 1.03) | 0.063 | 0.59 (0.32, 1.07) | 0.084 |
| No | 105 (73) | 70 (67) | — | — | — | |||
| Current smoking status | ||||||||
| Yes | 26 (18) | 13 (50) | 0.75 (0.39, 1.44) | 0.39 | 0.68 (0.31, 1.47) | 0.32 | 0.70 (0.33, 1.52) | 0.37 |
| No | 117 (82) | 83 (71) | — | — | — | |||
| No. doctor’s visits in previous year: | ||||||||
| < 4 | 48 (34) | 27 (56) | 0.52 (0.32, 0.85) | 0.026* | 0.47 (0.27, 0.82) | 0.026* | 0.51 (0.28, 0.91) | 0.053 |
| 4 – 12 | 70 (49) | 55 (79) | — | — | — | |||
| > 12 | 25 (17) | 14 (56) | 0.67 (0.35, 1.29) | 0.68 (0.29, 1.57) | 0.61 (0.27, 1.41) | |||
| General health status | ||||||||
| Fair/poor | 50 (35) | 31 (62) | 0.64 (0.40, 1.01) | 0.055 | 0.63 (0.36, 1.10) | 0.10 | 0.69 (0.39, 1.22) | 0.20 |
| Excellent/very good/good | 93 (65) | 65 (70) | — | — | — | |||
| History of arrhythmia | ||||||||
| Yes | 77 (54) | 53 (69) | 1.14 (0.74, 1.78) | 0.55 | 1.01 (0.57, 1.79) | 0.97 | 1.00 (0.57, 1.76) | >0.99 |
| No | 66 (46) | 43 (65) | — | — | — | |||
| No. variants in VKORC1 | ||||||||
| ≥1 | 59 (41) | 38 (64) | 0.96 (0.62, 1.47) | 0.84 | 1.06 (0.57, 1.98) | 0.85 | 1.01 (0.54, 1.88) | 0.97 |
| 0 | 84 (59) | 58 (69) | — | — | — | |||
All non-genetic factors, excluding adherence, are based on self-report. Age was excluded from this analysis to prevent over-adjustment, because it is a known strong predictor of warfarin adherence while being very weakly associated with TTM. Illegal injectable drug use was excluded because there were too few self-reported users in the subcohort to produce stable estimates.
Both unadjusted and adjusted results are from the same complete-case dataset to improve comparability; only individuals with adherence data were included in this analysis.
Individuals who failed to reach maintenance dose by the end of the study were considered censored.
All models are stratified by anticoagulation clinic site.
Hazard ratios and confidence intervals are based on the mean and variance from 1,000 bootstrap replications. Hazard ratios less than 1 indicate longer time to maintenance dose; hazard ratios greater than 1 indicate shorter time to maintenance dose.
All P-values are based on the Wald test using the mean and variance of estimates from 1,000 bootstrap replications. Categorical variables were tested jointly.
The adjusted model also included visit number to ensure that visit frequency was not confounding the time-varying covariate.
Adherence was specified in a time-varying fashion, indicating whether the participant had correct adherence on ≥ 80% of the days over the last 3 visits, using medication event monitoring system (MEMS) data.
P < 0.05