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- Title
Effects of grapefruit juice on the absorption of levothyroxine.
- Authors
Lilja, Jari J.; Laitinen, Kalevi; Neuvonen, Pertti J.
- Abstract
Our aim was to study the effect of grapefruit juice on the pharmacokinetics of levothyroxine. In a randomized cross-over study with two phases, 10 healthy subjects ingested 200 ml grapefruit juice or water (control) three times daily for 2 days. On day 3, a single 600 µg dose of levothyroxine was administered with 200 ml grapefruit juice or water, which was also ingested 1 h before and 1 h after levothyroxine. Serum concentrations of total thyroxine (T4) and thyroid-stimulating hormone (TSH) were measured up to 24 h. Grapefruit juice decreased slightly (11%; P < 0.01) the maximal increase of T4 concentration after ingestion of levothyroxine from 66.4 nmol l−1 to 59.4 nmol l−1 (95% CI on the difference −11.3, −2.7). The incremental areas under the serum T4 concentration-time curve (dAUC) during the first 4 and 6 h were also decreased slightly: dAUC(0,4 h) by 13% ( P < 0.05), from 195 nmol l−1 h to 169 nmol l−1 h (95% CI −51, −1) and dAUC(0,6 h) by 9% ( P = 0.085), from 298 nmol l−1 h to 271 nmol l−1 h (95% CI −58, 4). The decrease in the serum concentration of TSH (1.25 mU l−1) measured 24 h after ingestion of levothyroxine, was not altered by grapefruit juice. Grapefruit juice may slightly delay the absorption of levothyroxine, but it seems to have only a minor effect on its bioavailability. Accordingly, the clinical relevance of the grapefruit juice-levothyroxine interaction is likely to be small.
- Subjects
GRAPEFRUIT juice; CITRUS fruits; ABSORPTION; PHARMACOKINETICS; THYROXINE; THYROTROPIN
- Publication
British Journal of Clinical Pharmacology, 2005, Vol 60, Issue 3, p337
- ISSN
0306-5251
- Publication type
Article
- DOI
10.1111/j.1365-2125.2005.02433.x