title: Effects of pharmacological fiber supplements on levothyroxine absorption.
abstract: To determine the effect of pharmacological fiber supplements, we measured levothyroxine (LT4) absorption without and with simultaneous ingestion of either calcium polycarbophil or psyllium hydrophilic mucilloid. Serum thyroxine (T4) levels in 8 volunteers were measured following ingestion of 600 microg of LT4 on 3 separate occasions at 4-week intervals: (1) LT4 alone; (2) LT4 together with 1000 mg polycarbophil; and (3) LT4 together with 3.4 g psyllium. The amount of absorbed LT4 was calculated as the incremental rise in serum T4 level during the first 6 hours multiplied by the volume of distribution for the hormone, and expressed as a percentage of the dose administered. Absorption of LT4 alone averaged 89% (95% confidence interval [CI]: 75%-104%), occurring at a median of 180 minutes. After simultaneous ingestion of calcium polycarbophil, LT4 absorption was 86% (95% CI: 74%-97%), occurring at 180 minutes. With simultaneous ingestion of psyllium and LT4, the absorption was 80% (95% CI: 64%-95%), occurring at 240 minutes. In summary, neither calcium polycarbophil nor psyllium hydrophilic mucilloid are likely to cause malabsorption of LT4 that could be detected by these methods.
authors.affiliation: Department of Medical Specialties, University of Texas, M.D. Anderson Cancer Center, Houston 77030, USA.
authors.forename: A C
authors.initials: AC
authors.lastname: Chiu
authors.forename: S I
authors.initials: SI
authors.lastname: Sherman
mesh_terms: D000180:Acrylic Resins / Q000494:pharmacology*; D000328:Adult; D005260:Female; D006801:Humans; D007408:Intestinal Absorption / Q000187:drug effects*; D008297:Male; D011620:Psyllium / Q000494:pharmacology*; D011863:Radioimmunoassay; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood / Q000493:pharmacokinetics*
chemical_list: D000180:Acrylic Resins; D011620:Psyllium; C030312:calcium polycarbophil; D013972:Thyrotropin; D013974:Thyroxine