Drug interactions
Fosphenytoin + Oxycodone
Severity: Major
Fosphenytoin and Oxycodone: major 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
Fosphenytoin is converted to phenytoin, a strong CYP3A4 inducer, which can substantially lower oxycodone concentrations and reduce analgesia. Withdrawal symptoms may occur, and stopping the inducer can lead to oxycodone toxicity.
What this interaction means in plain words
Fosphenytoin and Oxycodone 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; Oxycodone belongs to Musculoskeletal.
Why it happens
Phenytoin induction of CYP3A4 increases oxycodone clearance.
What to do
Monitor pain control and withdrawal and increase the oxycodone dose if needed. If the anticonvulsant is withdrawn, lower the oxycodone dose and monitor for respiratory depression.
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?
Pro+ members
Unlock the full page
Create an account and start a Pro+ trial to unlock the full management advice for Fosphenytoin and Oxycodone, the additional notes, the evidence detail and the whole-prescription interaction checker.
- Full clinical management advice
- Additional notes
- Evidence detail
- Interaction checker for a whole prescription
Try Pro+ free for 7 days on the web. No card needed.
Other interactions of Oxycodone
- Alvimopan + Oxycodone Contraindicated
- Calcium / magnesium / potassium / sodium oxybates + Oxycodone Contraindicated
- Isocarboxazid + Oxycodone Contraindicated
- Olanzapine / samidorphan + Oxycodone Contraindicated
- Oxycodone + Phenelzine Contraindicated
- Oxycodone + Sodium oxybate 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 Oxycodone?
MediHelp rates the interaction as major. Fosphenytoin and Oxycodone 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 is converted to phenytoin, a strong CYP3A4 inducer, which can substantially lower oxycodone concentrations and reduce analgesia. Withdrawal symptoms may occur, and stopping the inducer can lead to oxycodone toxicity.
How serious is the interaction between Fosphenytoin and Oxycodone?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor pain control and withdrawal and increase the oxycodone dose if needed. If the anticonvulsant is withdrawn, lower the oxycodone dose and monitor for respiratory depression.
What other medicines interact with Oxycodone?
MediHelp also lists interactions of Oxycodone with, for example, Alvimopan, Calcium / magnesium / potassium / sodium oxybates, Isocarboxazid. The full list is on the Oxycodone page.
Full monographs, dosing and an interaction checker in the MediHelp app
Open the complete reference, check multi-drug interactions and use dosing tools in the MediHelp app.
