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Effects of grapefruit juice on the absorption of levothyroxine
Author(s) -
Lilja Jari J.,
Laitinen Kalevi,
Neuvonen Pertti J.
Publication year - 2005
Publication title -
british journal of clinical pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.216
H-Index - 146
eISSN - 1365-2125
pISSN - 0306-5251
DOI - 10.1111/j.1365-2125.2005.02433.x
Subject(s) - grapefruit juice , levothyroxine , absorption (acoustics) , medicine , pharmacology , chemistry , food science , pharmacokinetics , materials science , hormone , composite material
Aims Our aim was to study the effect of grapefruit juice on the pharmacokinetics of levothyroxine. Methods 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. Results 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. Conclusions 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.