Drug interactions
Fosphenytoin + Heparin
Severity: Moderate
Fosphenytoin and Heparin: 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, the active form of fosphenytoin, can alter anticoagulant response through protein-binding and enzyme effects. Evidence for a clinically important interaction with heparin is limited, and the legacy-style claim that heparin raises phenytoin levels is uncertain.
What this interaction means in plain words
Fosphenytoin and Heparin 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.
Fosphenytoin belongs to Central Nervous System; Heparin belongs to Cardiovascular.
Why it happens
Possible protein-binding displacement and enzyme effects of phenytoin; heparin may transiently raise free fatty acids and displace phenytoin, but the mechanism is not firmly established.
What to do
Monitor aPTT or anti-Xa and free phenytoin levels or seizure control when both are used. Adjust doses based on the results.
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 Heparin
- Defibrotide + Heparin Contraindicated
- Heparin + Ketorolac Contraindicated
- Heparin + Oritavancin Contraindicated
- Acemetacin + Heparin Major
- Acetylsalicylic acid + Heparin Major
- Alteplase + Heparin Major
Other interactions of Fosphenytoin
- Dronedarone + Fosphenytoin Contraindicated
- Fosphenytoin + Ledipasvir-sofosbuvir Contraindicated
- Fosphenytoin + Lorlatinib Contraindicated
- Fosphenytoin + Lurasidone Contraindicated
- Fosphenytoin + Ranolazine Contraindicated
- Fosphenytoin + Sofosbuvir-velpatasvir-voxilaprevir Contraindicated
Frequently asked questions
Can I take Fosphenytoin with Heparin?
MediHelp rates the interaction as moderate. Fosphenytoin and Heparin 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, the active form of fosphenytoin, can alter anticoagulant response through protein-binding and enzyme effects. Evidence for a clinically important interaction with heparin is limited, and the legacy-style claim that heparin raises phenytoin levels is uncertain.
How serious is the interaction between Fosphenytoin and Heparin?
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 aPTT or anti-Xa and free phenytoin levels or seizure control when both are used. Adjust doses based on the results.
What other medicines interact with Heparin?
MediHelp also lists interactions of Heparin with, for example, Defibrotide, Ketorolac, Oritavancin. The full list is on the Heparin page.
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