Potential cutaneous hypersensitivity reaction to an inactive ingredient of thyroid hormone supplements in a dog

Abstract

These elements strongly suggest that this dog had an idiosyncratic reaction (likely immune-mediated) against one or both inactive ingredients in the first two formulations of levothyroxine. We are not aware of any previous confirmed delayed hypersensitivity to a thyroid supplement in a dog with the likely chemical trigger being an inactive ingredient rather than the therapeutic agent itself. We hope that this case will raise awareness about allergic reactions to thyroid supplements and allergic reactions to inactive formulation components.

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“…In one case study describing a dog receiving levothyroxine for the treatment of hypothyroidism, it was suspected that certain excipient found in multiple formulations of the medications was the cause of a repeatable cutaneous adverse reaction. 57 This case report highlights the possibility that excipients may result in significant adverse reactions.…”

“…Although excipients are meant to be inert with regards to the efficacy of the active ingredient, there are reported adverse reactions suspected to be due to excipients. In one case study describing a dog receiving levothyroxine for the treatment of hypothyroidism, it was suspected that certain excipient found in multiple formulations of the medications was the cause of a repeatable cutaneous adverse reaction 57 . This case report highlights the possibility that excipients may result in significant adverse reactions.…”

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“…It is unlikely that this reflects an adverse effect of the treatment itself as thyroxine supplementation is usually well tolerated [ 28 ]. Only in rare cases, hypersensitivity reactions affecting the skin have been demonstrated where inactive ingredients of the levothyroxine tablet were the suspected cause [ 29 ], however as there was no question to evaluate either the onset of signs it is not possible to draw any conclusion to the underlying aetiology of the skin problems and GSD`s are a breed predisposed for atopy and pyoderma [ 30 ].…”