Drug interactions
Phenytoin + Thyroid desiccated
Severity: Moderate
Phenytoin and Thyroid desiccated: moderate interaction.
Last updated
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Phenytoin can lower circulating thyroid hormone levels, so patients on desiccated thyroid may develop hypothyroid symptoms or a rising TSH. The effect is more relevant in patients with limited thyroid reserve who depend on replacement.
What this interaction means in plain words
Phenytoin and Thyroid desiccated can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Why it happens
Phenytoin induces hepatic metabolism of thyroid hormones and may displace them from binding proteins.
What to do
Monitor TSH and free thyroid hormone levels after starting or stopping phenytoin. Increase the thyroid dose as needed.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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Other interactions of Phenytoin
- Artemether / lumefantrine + Phenytoin Contraindicated
- Bictegravir + Phenytoin Contraindicated
- Cabotegravir + Phenytoin Contraindicated
- Doravirine + Phenytoin Contraindicated
- Elbasvir / grazoprevir + Phenytoin Contraindicated
- Elvitegravir / cobicistat / emtricitabine / tenofovir df + Phenytoin Contraindicated
Frequently asked questions
Can I take Phenytoin with Thyroid desiccated?
MediHelp rates the interaction as moderate. Phenytoin and Thyroid desiccated can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Phenytoin can lower circulating thyroid hormone levels, so patients on desiccated thyroid may develop hypothyroid symptoms or a rising TSH. The effect is more relevant in patients with limited thyroid reserve who depend on replacement.
How serious is the interaction between Phenytoin and Thyroid desiccated?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor TSH and free thyroid hormone levels after starting or stopping phenytoin. Increase the thyroid dose as needed.
What other medicines interact with Phenytoin?
MediHelp also lists interactions of Phenytoin with, for example, Artemether / lumefantrine, Bictegravir, Cabotegravir. The full list is on the Phenytoin page.
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