What the FDA labels say about taking them together
Carbidopa/entacapone/levodopa and phenytoin
Carbidopa/entacapone/levodopa's FDA label of March 19, 2026 names phenytoin in its drug interactions section; the phenytoin labels PlainMeds reads (2) do not name carbidopa/entacapone/levodopa. The carbidopa/entacapone/levodopa label: “Dopamine D2 receptor antagonists, isoniazid, phenytoin, papaverine and iron salts: may reduce efficacy of carbidopa, levodopa and entacapone tablets”
Check it at the source: the carbidopa/entacapone/levodopa FDA label on DailyMed (effective March 19, 2026, Sandoz Inc); the phenytoin FDA label on DailyMed (effective October 15, 2024, Mylan Pharmaceuticals Inc.).
What does the carbidopa/entacapone/levodopa label say about phenytoin?
Carbidopa/entacapone/levodopa label, drug interactionsDopamine D2 receptor antagonists, isoniazid, phenytoin, papaverine and iron salts: may reduce efficacy of carbidopa, levodopa and entacapone tablets
Source: FDA drug label (Carbidopa, Levodopa, and Entacapone), NDA021485 (Orion Pharma), as published by Sandoz Inc, effective March 19, 2026 (SPL set 9c16c0e0-3b97-486b-b7d5-579f5853e2c5), via openFDA; the full label on DailyMed
What does the phenytoin label say about carbidopa/entacapone/levodopa?
Phenytoin's label (effective October 15, 2024) and its 1 other brand-application label do not name carbidopa/entacapone/levodopa in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (Phenytek), Mylan Pharmaceuticals Inc., effective October 15, 2024 (SPL set 0f94c791-8b07-4b41-927e-c9f28bec5f60), 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
| Carbidopa/entacapone/levodopa | Phenytoin | |
|---|---|---|
| Labeled for | Parkinson's disease | Seizures and epilepsy |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $0.695 per tablet 25-100-200 mg tablet | $0.145 per capsule 100 mg capsule |
| 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