What the FDA labels say about taking them together
Fosphenytoin and quetiapine
Fosphenytoin's FDA label of May 18, 2025 names quetiapine in its drug interactions section; the quetiapine labels PlainMeds reads (2) do not name fosphenytoin. The fosphenytoin label: “Interacting Agent: Other; Examples: Albendazole, chlorpropamide, clozapine, cyclosporine, digoxin, disopyramide, folic acid, methadone, mexiletine, praziquantel, quetiapine”
Check it at the source: the fosphenytoin FDA label on DailyMed (effective May 18, 2025, Pfizer Laboratories Div Pfizer Inc); the quetiapine FDA label on DailyMed (effective April 10, 2026, H2-Pharma, LLC).
What does the fosphenytoin label say about quetiapine?
Fosphenytoin label, drug interactionsInteracting Agent: Other; Examples: Albendazole (decreases active metabolite), chlorpropamide, clozapine, cyclosporine, digoxin, disopyramide, folic acid, methadone, mexiletine, praziquantel, quetiapine
Source: FDA drug label (CEREBYX), NDA020450 (Parke Davis), as published by Pfizer Laboratories Div Pfizer Inc, effective May 18, 2025 (SPL set de5a6711-4abb-4c3d-a18b-266b094ace11), via openFDA; the full label on DailyMed
What does the quetiapine label say about fosphenytoin?
Quetiapine's label (effective April 10, 2026) and its 1 other brand-application label do not name fosphenytoin in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (SEROQUEL), NDA020639 (Cheplapharm), as published by H2-Pharma, LLC, effective April 10, 2026 (SPL set 8ae62aaf-f8c5-417f-baac-0098369ca322), 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
| Fosphenytoin | Quetiapine | |
|---|---|---|
| Labeled for | Seizures and epilepsy | Schizophrenia, Bipolar disorder, Depression |
| Boxed warning | Yes | Yes |
| Pharmacy cost (NADAC) | n/a | $0.127 per tablet 300 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