Phenytoin and Rifampicin: Drug Interaction Guide
Quick answer: This is a major interaction — avoid combining Phenytoin and Rifampicin unless specifically directed by your doctor.
How Phenytoin interacts with Rifampicin
Rifampicin is a potent inducer of CYP2C9, CYP2C19 and CYP3A4, accelerating phenytoin metabolism and lowering its serum concentration.
What you should do
Monitor phenytoin levels and seizure control; anticipate the need for dose increases on starting and reductions on stopping rifampicin.
Key facts
Severity
Major — avoid combination
Mechanism
Rifampicin is a potent inducer of CYP2C9, CYP2C19 and CYP3A4, accelerating phenytoin metabolism and lowering its serum c...
Action
Monitor phenytoin levels and seizure control; anticipate the need for dose increases on starting and reductions on stopp...
Frequently asked questions
Can I take Phenytoin and Rifampicin together?
No — this combination should generally be avoided. Monitor phenytoin levels and seizure control; anticipate the need for dose increases on starting and reductions on stopping rifampicin.
What is the severity of this interaction?
The interaction between Phenytoin and Rifampicin is classified as Major — avoid combination. Rifampicin is a potent inducer of CYP2C9, CYP2C19 and CYP3A4, accelerating phenytoin metabolism and lowering its serum concentration.
What should I do if I'm prescribed both?
Monitor phenytoin levels and seizure control; anticipate the need for dose increases on starting and reductions on stopping rifampicin. Always consult your prescribing clinician — do not stop or change medications without medical guidance.
Last reviewed: by iMedic Medical Editorial Team. Our editorial process.