Drug interactions
Phenindione + Propylthiouracil
Severity: Moderate
Phenindione and Propylthiouracil: 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
Treating hyperthyroidism with propylthiouracil lowers the catabolism of vitamin K-dependent clotting factors, which can reduce the effect of oral anticoagulants. When thyroid function is restored, the anticoagulant effect rises, and propylthiouracil may itself cause hypoprothrombinemia.
What this interaction means in plain words
Phenindione and Propylthiouracil 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
Changes in thyroid status alter clotting factor turnover, and propylthiouracil may reduce vitamin K-dependent factor synthesis.
What to do
Monitor INR or prothrombin time closely when starting, changing or stopping propylthiouracil. Adjust the anticoagulant dose as thyroid function normalizes.
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 Propylthiouracil
Frequently asked questions
Can I take Phenindione with Propylthiouracil?
MediHelp rates the interaction as moderate. Phenindione and Propylthiouracil 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. Treating hyperthyroidism with propylthiouracil lowers the catabolism of vitamin K-dependent clotting factors, which can reduce the effect of oral anticoagulants. When thyroid function is restored, the anticoagulant effect rises, and propylthiouracil may itself cause hypoprothrombinemia.
How serious is the interaction between Phenindione and Propylthiouracil?
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 INR or prothrombin time closely when starting, changing or stopping propylthiouracil. Adjust the anticoagulant dose as thyroid function normalizes.
What other medicines interact with Propylthiouracil?
MediHelp also lists interactions of Propylthiouracil with, for example, Carbamazepine, Clozapine, Methimazole. The full list is on the Propylthiouracil page.
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