What the FDA labels say about taking them together
Levoleucovorin and primidone
Levoleucovorin's FDA label of August 29, 2023 names primidone in its drug interactions section; the primidone label PlainMeds reads does not name levoleucovorin. The levoleucovorin label: “… amounts may counteract the antiepileptic effect of phenobarbital, phenytoin and primidone and increase the frequency of seizures in susceptible children.”
Check it at the source: the levoleucovorin FDA label on DailyMed (effective August 29, 2023, Slate Run Pharmaceuticals); the primidone FDA label on DailyMed (effective September 10, 2026, Bausch Health US, LLC).
What does the levoleucovorin label say about primidone?
Levoleucovorin label, drug interactionsDRUG INTERACTIONS 7.1 Effects of Leucovorin Products on Other Drugs Antiepileptic Drugs Folic acid in large amounts may counteract the antiepileptic effect of phenobarbital, phenytoin and primidone and increase the frequency of seizures in susceptible children.
Source: FDA drug label (LEVOLEUCOVORIN CALCIUM), Slate Run Pharmaceuticals, effective August 29, 2023 (SPL set 124bc214-62f8-40f9-a227-a35e2d1ff2a0), via openFDA; the full label on DailyMed
What does the primidone label say about levoleucovorin?
Primidone's label (effective September 10, 2026) does not name levoleucovorin in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (Mysoline), NDA009170 (Valeant), as published by Bausch Health US, LLC, effective September 10, 2026 (SPL set af593171-dabb-4ea3-b44c-89ed457b2c46), via openFDA; the full label on DailyMed
These are the labels' own sentences. PlainMeds does not grade interactions; a pharmacist or prescriber can say what they mean for one person's medicines.
Both medicines on the record
| Levoleucovorin | Primidone | |
|---|---|---|
| Labeled for | Colorectal cancer | Seizures and epilepsy |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | n/a | $0.0914 per tablet 50 mg tablet |
| Shortage now | No current entry | No current entry |
Source: FDA NDC Directory, CMS NADAC of October 7, 2026 and the FDA Drug Shortage Database (FDA files October 8, 2026)
What next?
- Check more medicines together
- up to five at once