Drug interactions
Fosphenytoin + Losartan
Severity: Moderate
Fosphenytoin and Losartan: 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, induces CYP2C9 and CYP3A4 and may lower exposure to losartan and its active metabolite. This could reduce blood pressure control.
What this interaction means in plain words
Fosphenytoin and Losartan 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; Losartan belongs to Cardiovascular.
Why it happens
Enzyme induction of CYP2C9 and CYP3A4 increases losartan metabolic clearance.
What to do
Monitor blood pressure when fosphenytoin is started or stopped, and increase the losartan dose if control is lost.
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 Losartan
- Aliskiren + Losartan Contraindicated
- Losartan + Sparsentan Contraindicated
- Amifostine + Losartan Major
- Amiloride + Losartan Major
- Amlodipine-benazepril + Losartan Major
- Amlodipine-hydrochlorothiazide-valsartan + Losartan 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 Losartan?
MediHelp rates the interaction as moderate. Fosphenytoin and Losartan 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, induces CYP2C9 and CYP3A4 and may lower exposure to losartan and its active metabolite. This could reduce blood pressure control.
How serious is the interaction between Fosphenytoin and Losartan?
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 blood pressure when fosphenytoin is started or stopped, and increase the losartan dose if control is lost.
What other medicines interact with Losartan?
MediHelp also lists interactions of Losartan with, for example, Aliskiren, Sparsentan, Amifostine. The full list is on the Losartan page.
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