Drug interactions
Fosphenytoin + Posaconazole
Severity: Major
Fosphenytoin and Posaconazole: major interaction.
Last updated Sources: US FDA label
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 product of fosphenytoin, lowers posaconazole concentrations and may lead to antifungal treatment failure. Posaconazole may in turn raise phenytoin levels, increasing the risk of phenytoin toxicity.
What this interaction means in plain words
Fosphenytoin and Posaconazole can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Fosphenytoin belongs to Central Nervous System; Posaconazole belongs to Anti Fungals.
Why it happens
Phenytoin induces UGT-mediated glucuronidation and P-gp efflux of posaconazole, while posaconazole may inhibit CYP-mediated phenytoin metabolism.
What to do
Avoid the combination unless the benefit outweighs the risk. If used, monitor posaconazole trough concentrations and phenytoin levels with dose adjustment.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
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References
Other interactions of Posaconazole
- Artemether + Posaconazole Contraindicated
- Avanafil + Posaconazole Contraindicated
- Cobimetinib + Posaconazole Contraindicated
- Conivaptan + Posaconazole Contraindicated
- Dihydroergotamine intranasal + Posaconazole Contraindicated
- Dihydroergotamine + Posaconazole 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 Posaconazole?
MediHelp rates the interaction as major. Fosphenytoin and Posaconazole can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. Phenytoin, the active product of fosphenytoin, lowers posaconazole concentrations and may lead to antifungal treatment failure. Posaconazole may in turn raise phenytoin levels, increasing the risk of phenytoin toxicity.
How serious is the interaction between Fosphenytoin and Posaconazole?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid the combination unless the benefit outweighs the risk. If used, monitor posaconazole trough concentrations and phenytoin levels with dose adjustment.
What other medicines interact with Posaconazole?
MediHelp also lists interactions of Posaconazole with, for example, Artemether, Avanafil, Cobimetinib. The full list is on the Posaconazole page.
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