Table 1.
Pharmacokinetics of a single 600 µg dose of levothyroxine in 10 subjects after co-administration with water or grapefruit juice
| Variable | Water phase | Grapefruit juice phase | Mean difference (95% CI) between phases |
|---|---|---|---|
| T4 at baseline (nmol l−1) | 87.7 ± 7.8 | 84.5 ± 11.9 | −3.2 (−13.8, 7.4) |
| dCmax (nmol l−1) | 66.4 ± 10.5 | 59.4 ± 7.4** | −7.0 (−11.3, −2.7) |
| Percentage of control (range) | 100% | 89% (78–107%) | |
| tmax (h) | 1.75 (1.5–4) | 3 (1–4) | 0.8 (−0.4, 1.9) |
| dAUC(0,4 h) (nmol l−1 h) | 195 ± 42.1 | 169 ± 31.2* | −26 (−51, −1) |
| Percentage of control (range) | 100% | 87% (62–134%) | |
| dAUC(0,6 h) (nmol l−1 h) | 298 ± 58.6 | 271 ± 43.2† | −27 (−58, 4) |
| Percentage of control (range) | 100% | 91% (76–128%) | |
| Levothyroxine absorbed (µg) | 511 ± 87.7 | 457 ± 59.9** | −54 (−90, −19) |
| Percentage of dose (range) | 85% (58–110%) | 76% (56–91%) | |
| TSH (mU l−1) before levothyroxine | 1.79 ± 0.94 | 1.86 ± 0.95 | 0.07 (−0.29, 0.42) |
| dTSH (mU l−1) after levothyroxine | 1.25 ± 0.72 | 1.22 ± 0.72 | −0.03 (−0.33, 0.26) |
Data are mean values (± SD); tmax values are given as median with ranges. dCmax, maximal increase in serum concentration of thyroxine (T4); tmax, time to reach dCmax; dAUC(0,t), incremental area under the serum concentration-time curve from zero to t h; levothyroxine absorbed is calculated by multiplying the dCmax of T4 by the estimated volume of distribution of levothyroxine; TSH, thyroid-stimulating hormone; dTSH, serum TSH at 24 h minus the baseline TSH (at time 0).
**
P < 0.01 vs. water phase (control),
*
P < 0.05 vs. water phase,
†
P = 0.085 vs. water phase.