Drug interactions
Fosphenytoin + Tadalafil
Severity: Moderate
Fosphenytoin and Tadalafil: 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 CYP3A4 and can markedly reduce tadalafil levels. This can lead to loss of efficacy.
What this interaction means in plain words
Fosphenytoin and Tadalafil 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; Tadalafil belongs to Genitourinary.
Why it happens
Induction of CYP3A4 by phenytoin increases tadalafil clearance.
What to do
Avoid in pulmonary arterial hypertension. For erectile dysfunction, monitor response and consider dose adjustment or an alternative.
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 Tadalafil
- Amyl nitrite + Tadalafil Contraindicated
- Isosorbide dinitrate + Tadalafil Contraindicated
- Isosorbide mononitrate + Tadalafil Contraindicated
- Nitroglycerin po + Tadalafil Contraindicated
- Nitroglycerin rectal + Tadalafil Contraindicated
- Nitroglycerin sublingual + Tadalafil Contraindicated
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 Tadalafil?
MediHelp rates the interaction as moderate. Fosphenytoin and Tadalafil 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 CYP3A4 and can markedly reduce tadalafil levels. This can lead to loss of efficacy.
How serious is the interaction between Fosphenytoin and Tadalafil?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid in pulmonary arterial hypertension. For erectile dysfunction, monitor response and consider dose adjustment or an alternative.
What other medicines interact with Tadalafil?
MediHelp also lists interactions of Tadalafil with, for example, Amyl nitrite, Isosorbide dinitrate, Isosorbide mononitrate. The full list is on the Tadalafil page.
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