QuestionAugust 17, 2025

Which pharmacologic agent is most likely to cause increased toxicity of levothyroxine? Cholestyramine Magnesium antacids Sucralfate Tricyclic antidepressants Simethicone

Which pharmacologic agent is most likely to cause increased toxicity of levothyroxine? Cholestyramine Magnesium antacids Sucralfate Tricyclic antidepressants Simethicone
Which pharmacologic agent is most likely to cause increased toxicity of levothyroxine?
Cholestyramine
Magnesium antacids
Sucralfate
Tricyclic antidepressants
Simethicone

Solution
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Answer

Cholestyramine Explanation 1. Identify the interaction mechanism Levothyroxine absorption can be affected by agents that bind or interfere with its uptake in the gastrointestinal tract. 2. Analyze each option - **Cholestyramine**: Binds to levothyroxine, reducing its absorption. - Magnesium antacids: May interfere but not as significantly. - Sucralfate: Can bind and reduce absorption but less commonly noted. - Tricyclic antidepressants: No significant effect on levothyroxine absorption. - Simethicone: Does not affect levothyroxine absorption. 3. Determine the most likely agent Cholestyramine is known for significantly binding to levothyroxine, leading to decreased absorption and increased toxicity risk due to altered levels.

Explanation

1. Identify the interaction mechanism<br /> Levothyroxine absorption can be affected by agents that bind or interfere with its uptake in the gastrointestinal tract.<br /><br />2. Analyze each option<br /> - **Cholestyramine**: Binds to levothyroxine, reducing its absorption.<br /> - Magnesium antacids: May interfere but not as significantly.<br /> - Sucralfate: Can bind and reduce absorption but less commonly noted.<br /> - Tricyclic antidepressants: No significant effect on levothyroxine absorption.<br /> - Simethicone: Does not affect levothyroxine absorption.<br /><br />3. Determine the most likely agent<br /> Cholestyramine is known for significantly binding to levothyroxine, leading to decreased absorption and increased toxicity risk due to altered levels.
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