Table 1. Baseline Characteristics of Cohort 1a.
| Characteristic | Prematch | 1:1 matchb | ||||
|---|---|---|---|---|---|---|
| Levothyroxine group | SMDc | Levothyroxine group | SMDc | |||
| Generic (n = 15 299) | Brand-name (n = 2299) | Generic (n = 2285) | Brand-name (n = 2285) | |||
| Initiating dose, μg/d | ||||||
| ≤50 | 13 245 (86.6) | 1875 (81.6) | −0.14 | 1899 (83.1) | 1865 (81.6) | −0.04 |
| 51-100 | 1799 (11.8) | 357 (15.5) | 0.11 | 334 (14.6) | 355 (15.5) | 0.03 |
| 101-200 | 255 (1.7) | 67 (2.9) | 0.08 | 52 (2.3) | 65 (2.8) | 0.03 |
| Thyrotropin level, mIU/L | ||||||
| 4.5-9.9 | 13 340 (87.2) | 2027 (88.2) | 0.03 | 2041 (89.3) | 2015 (88.2) | −0.03 |
| 10.0-19.9 | 1959 (12.8) | 272 (11.8) | −0.03 | 244 (10.7) | 270 (11.8) | 0.03 |
| Mean (SD) | 7.0 (2.8) | 6.9 (2.8) | 0.04 | 6.8 (2.6) | 6.9 (2.8) | −0.04 |
| Median (IQR) | 6.1 (5.2-7.8) | 6.0 (5.1-7.7) | NA | 5.9 (5.1-7.5) | 6.0 (5.1-7.6) | NA |
| Age, y | ||||||
| Mean (SD) | 55.8 (16.2) | 50.4 (13.7) | 0.36 | 50.2 (13.8) | 50.4 (13.7) | −0.02 |
| Median (IQR) | 56.0 (45.0-68.0) | 51.0 (41.0-60.0) | NA | 50.0 (41.0-60.0) | 51.0 (41.0-60.0) | NA |
| Sex | ||||||
| Female | 10 410 (68.0) | 1726 (75.1) | 0.16 | 1741 (76.2) | 1716 (75.1) | −0.03 |
| Male | 4889 (32.0) | 573 (24.9) | −0.16 | 544 (23.8) | 569 (24.9) | 0.03 |
| Race/ethnicity | ||||||
| Asian | 659 (4.3) | 107 (4.7) | 0.02 | 92 (4.0) | 104 (4.6) | 0.03 |
| Black | 1281 (8.4) | 177 (7.7) | −0.03 | 164 (7.2) | 173 (7.6) | 0.02 |
| Hispanic | 1572 (10.3) | 206 (9.0) | −0.04 | 187 (8.2) | 206 (9.0) | 0.03 |
| White | 11 289 (73.8) | 1734 (75.4) | 0.04 | 1783 (78.0) | 1727 (75.6) | −0.06 |
| Unknown | 498 (3.3) | 75 (3.3) | 0 | 59 (2.6) | 75 (3.3) | 0.04 |
| Insurance plan | ||||||
| Commercial | 10 527 (68.8) | 2032 (88.4) | 0.49 | 2020 (88.4) | 2018 (88.3) | 0 |
| Medicare Advantage | 4772 (31.2) | 267 (11.6) | −0.49 | 265 (11.6) | 267 (11.7) | 0 |
| Census region | ||||||
| Midwest | 1961 (12.8) | 212 (9.2) | −0.12 | 200 (8.8) | 212 (9.3) | 0.02 |
| Northeast | 1500 (9.8) | 211 (9.2) | −0.02 | 218 (9.5) | 209 (9.1) | −0.01 |
| South | 9024 (59.0) | 1573 (68.4) | 0.2 | 1552 (67.9) | 1562 (68.4) | 0.01 |
| West | 2814 (18.4) | 303 (13.2) | −0.15 | 315 (13.8) | 302 (13.2) | −0.02 |
| Charlson comorbidity index score at baseline | ||||||
| Mean (SD) | 1.1 (1.9) | 0.7 (1.4) | 0.24 | 0.6 (1.2) | 0.7 (1.4) | −0.08 |
| Median (IQR) | 0 (0-1.0) | 0 (0-1.0) | NA | 0 (0-1.0) | 0 (0-1.0) | NA |
| Conditions affecting levothyroxine absorption | ||||||
| Inflammatory bowel disease | 109 (0.7) | 22 (1.0) | 0.03 | 13 (0.6) | 21 (0.9) | 0.04 |
| Anemia | 892 (5.8) | 120 (5.2) | −0.03 | 108 (4.7) | 120 (5.3) | 0.03 |
| Estrogen use 90 d prior | 1648 (10.8) | 377 (16.4) | 0.16 | 342 (15.0) | 375 (16.4) | 0.04 |
| Prescribing physician specialty | ||||||
| Endocrinologist | 719 (4.7) | 438 (19.1) | 0.46 | 414 (18.1) | 425 (18.6) | 0.01 |
| General | 11 345 (74.2) | 1507 (65.6) | −0.19 | 1523 (66.7) | 1507 (66.0) | −0.01 |
| Missing/other | 3235 (21.1) | 354 (15.4) | −0.15 | 348 (15.2) | 353 (15.4) | 0.01 |
Abbreviations: IQR, interquartile range; NA, not applicable; SMD, standardized mean difference.
a
Includes adult patients who newly filled generic or brand-name levothyroxine preparations from January 1, 2008, to October 1, 2017. Unless otherwise indicated, data are expressed as number (percentage) of patients. Percentages have been rounded and may not total 100.
b
Also matched on year of index prescription.
c
A baseline characteristic was considered balanced if the maximum SMD was less than 0.10.