Gluten and Aluminum Content in Synthroid® (Levothyroxine Sodium Tablets)

Abstract

IntroductionInquiries from healthcare providers and patients about the gluten and aluminum content of Synthroid® (levothyroxine sodium tablets) have increased. The objective of this study was to measure and evaluate the gluten content of the raw materials used in the manufacturing of Synthroid. Additionally, this study determined the aluminum content in different strengths of Synthroid tablets by estimating the amount of aluminum in the raw materials used in the manufacturing of Synthroid.MethodsGluten levels of three lots of the active pharmaceutical ingredient (API) and one lot of each excipient from different vendors were examined. The ingredients in all current Synthroid formulations (strengths) were evaluated for their quantity of aluminum.ResultsGluten concentrations were below the lowest limit of detection (<3.0 ppm) for all tested lots of the API and excipients of Synthroid tablets. Aluminum content varied across tablet strengths (range 19–137 µg/tablet). Gluten levels of the API and excipients were found to be below the lowest level of detection and are considered gluten-free based on the US Food and Drug Administration (FDA) definition for food products. Across the various tablet strengths of Synthroid, the maximum aluminum levels were well below the FDA-determined minimal risk level for chronic oral aluminum exposure (1 mg/kg/day).ConclusionThese data demonstrate that Synthroid tablets are not a source for dietary gluten and are a minimal source of aluminum.FundingAbbVie Inc.

Levothyroxine Formulations: Pharmacological and Clinical Implications of Generic Substitution

“…However, most studies showing better absorption with soft gel or liquid LT4 formulations compared with tablets were published after the ATA guidelines were released. As a result, there are no specific recommendations for the use of such formulations in these circumstances, but it has been suggested that they may be useful in patients with allergies or side effects to the excipients found in some LT4 tablets (e.g., lactose in Synthroid) [3, 54–56].…”

An uncommon case of rhabdomyolysis in severe hypothyroidism

“…Intolerance to synthroid in our patient could be due to gluten content, although she was unaware of gluten sensitivity in her regular diet. 10 Also, different levothyroxine preparations may exhibit differences in the bioequivalence. 7 As the concern was of intolerability rather than the bioavailability, the decision was made to equate the dose of eltroxin early.…”