What the FDA labels say about taking them together
Pentobarbital and phenytoin
Pentobarbital's FDA label of March 8, 2024 names phenytoin in its drug interactions section; the phenytoin labels PlainMeds reads (2) do not name pentobarbital. The pentobarbital label: “Because the effect of barbiturates on the metabolism of phenytoin is not predictable, phenytoin and barbiturate blood levels should be monitored more frequently if these drugs are given concurrently.”
Check it at the source: the pentobarbital FDA label on DailyMed (effective March 8, 2024, Hikma Pharmaceuticals USA Inc.); the phenytoin FDA label on DailyMed (effective October 15, 2024, Mylan Pharmaceuticals Inc.).
What does the pentobarbital label say about phenytoin?
Pentobarbital label, drug interactionsBecause the effect of barbiturates on the metabolism of phenytoin is not predictable, phenytoin and barbiturate blood levels should be monitored more frequently if these drugs are given concurrently.
Source: FDA drug label (Pentobarbital Sodium), Hikma Pharmaceuticals USA Inc., effective March 8, 2024 (SPL set d375b92a-baa1-4d63-9ad1-1467dcfde7d5), via openFDA; the full label on DailyMed
What does the phenytoin label say about pentobarbital?
Phenytoin's label (effective October 15, 2024) and its 1 other brand-application label do not name pentobarbital 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
| Pentobarbital | Phenytoin | |
|---|---|---|
| Labeled for | Insomnia | Seizures and epilepsy |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | n/a | $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