Felodipine and Primidone: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Primidone
Felodipine
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Reduced felodipine exposure and reduced efficacy of felodipine
Interaction Deep Dive
Concomitant use of PHENobarbital (a CYP3A inducer) with felodipine (a CYP3A substrate) may decrease felodipine exposure, which may reduce the efficacy of felodipine. If concomitant use cannot be avoided, closely monitor neonates and consider increasing the felodipine accordingly3. Maximum plasma concentrations of felodipine were lower in 10 epileptic patients on long-term anticonvulsant therapy (phenytoin, carbamazepine, PHENobarbital) than in 12 healthy volunteers after administration of oral felodipine 5 mg twice daily for four days in both groups 41.
Why it happens (mechanism)
Induction of CYP3A-mediated metabolism of felodipine; increased hepatic metabolism
Literature reports
1 report — tap to read
a) Maximum plasma concentrations of felodipine were considerably lower in 10 epileptic patients (1.6 nmol/L) on long-term anticonvulsant therapy (phenytoin, carbamazepine, PHENobarbital) than in 12 healthy volunteers (8.7 nmol/L) after administration of oral felodipine 5 mg twice daily for four days to both groups 2. The mean area under the felodipine plasma concentration-time curve at 12 hours postdose was reduced from 33 nmol/L/hr in the volunteers to 2 nmol/L/hr in epileptics on anticonvulsant medications. Induction of hepatic microsomal enzymes by anticonvulsant drugs is the proposed mechanism for the observed interaction. Higher felodipine dosages will be required to reduce blood pressure in patients taking anticonvulsant medications 1.
Common questions
Can I take Felodipine and Primidone together?
Reduced felodipine exposure and reduced efficacy of felodipine Always confirm with your pharmacist or prescriber before making any change.
How serious is the Felodipine and Primidone interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Felodipine or Primidone need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there a safer alternative to one of these medications for me?
References (4)
- Saltiel E, Ellrodt AG, Monk JP, et al: Felodipine: a review of its pharmacodynamic and pharmacokinetic properties, and therapeutic use in hypertension. Drugs 1988; 36:387-428.
- Capewell S, Freestone S, Critchley JAJH, et al: Gross reduction in felodipine bioavailability in patients taking anticonvulsants. Br J Clin Pharmacol 1987; 24:243P-244P.
- Product Information: SEZABY(TM) intravenous injection, phenobarbital sodium intravenous injection. Sun Pharmaceutical Industries Inc (per manufacturer), Cranbury, NJ, 2022. DailyMed
- Capewell S, Freestone S, Critchley JAJH, et al: Gross reduction in felodipine bioavailabiltiy in patients taking anticonvulsants. Br J Clin Pharmacol 1987; 24:243P-244P.
Keep reading about Primidone
Keep reading about Felodipine
These medications also interact with supplements
Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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