What the FDA labels say about taking them together
Ethosuximide and valproic acid
Ethosuximide's FDA label (Zarontin) of May 25, 2026 names valproic acid in its drug interactions section, and valproic acid's label names ethosuximide too. The ethosuximide label: “Drug Interactions: Since Zarontin (ethosuximide) may interact with concurrently administered antiepileptic drugs, periodic serum level determinations of these drugs may be necessary.”
Check it at the source: the ethosuximide FDA label on DailyMed (effective June 11, 2026, Chartwell Governmental & Specialty RX, LLC.); the valproic acid FDA label on DailyMed (effective January 24, 2025, PAI Holdings, LLC dba PAI Pharma).
What does the ethosuximide label say about valproic acid?
Zarontin label (Parke-Davis Div of Pfizer Inc, May 25, 2026), drug interactionsDrug Interactions: Since Zarontin (ethosuximide) may interact with concurrently administered antiepileptic drugs, periodic serum level determinations of these drugs may be necessary (e.g., ethosuximide may elevate phenytoin serum levels and valproic acid has been reported to both increase and decrease ethosuximide levels).
Source: FDA drug label (Zarontin, NDA012380), Parke-Davis Div of Pfizer Inc, effective May 25, 2026 (SPL set 0e008f33-70a1-4bc6-b3a0-d45214418ab6), via openFDA
Source: FDA drug label (Ethosuximide), Chartwell Governmental & Specialty RX, LLC., effective June 11, 2026 (SPL set a825265d-ace9-4463-a16d-f6d5e1e31188), via openFDA; the full label on DailyMed
What does the valproic acid label say about ethosuximide?
Valproic acid label, drug interactionsMonitoring of valproate concentrations is recommended ( 7.1 ) Co-administration of valproate can affect the pharmacokinetics of other drugs (e.g., diazepam, ethosuximide, lamotrigine, phenytoin) by inhibiting their metabolism or protein binding displacement ( 7.2 ) Patients stabilized on rufinamide should begin valproate therapy at a low dose, and titrate to clinically effective dose ( 7.2 ) Dosage adjustment of amitriptyline/nortriptyline, propofol, warfarin, and zidovudine may be necessary if used concomitantly with Valproic acid ( 7.2 ) Topiramate: Hyperammonemia and encephalopathy
Source: FDA drug label (VALPROIC ACID), PAI Holdings, LLC dba PAI Pharma, effective January 24, 2025 (SPL set 7d5cb52e-37dd-4dfa-a6f4-09f9548846c6), 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
| Ethosuximide | Valproic acid | |
|---|---|---|
| Labeled for | Seizures and epilepsy | Seizures and epilepsy, Migraine |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | $0.243 per capsule 250 mg capsule | $0.243 per capsule 250 mg capsule |
| Shortage now | No current entry | Listed; available |
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