What the FDA labels say about taking them together
Meperidine and phenytoin
Meperidine's FDA label of November 29, 2025 names phenytoin in its drug interactions section; the phenytoin labels PlainMeds reads (2) do not name meperidine. The meperidine label: “The concomitant use of meperidine hydrochloride tablets and CYP3A4 or CYP2B6 inducers can decrease the plasma concentration of meperidine, resulting in decreased efficacy or onset of a withdrawal syndrome in patients …”
Check it at the source: the meperidine FDA label on DailyMed (effective November 29, 2025, EPIC PHARMA, LLC); the phenytoin FDA label on DailyMed (effective October 15, 2024, Mylan Pharmaceuticals Inc.).
What does the meperidine label say about phenytoin?
Meperidine label, drug interactionsCYP3A4 and CYP2B6 Inducers Clinical Impact: The concomitant use of meperidine hydrochloride tablets and CYP3A4 or CYP2B6 inducers can decrease the plasma concentration of meperidine, resulting in decreased efficacy or onset of a withdrawal syndrome in patients who have developed physical dependence to meperidine. … frequent intervals for signs of respiratory depression and sedation. Examples: Rifampin, carbamazepine, phenytoin
Meperidine label, warnings and precautionsSimilarly, discontinuation of a CYP3A4 inducer, such as rifampin, carbamazepine, and phenytoin, in meperidine hydrochloride tablets-treated patients may increase meperidine plasma concentrations and prolong opioid adverse reactions.
Source: FDA drug label (Demerol, NDA021171), Hospira, Inc., effective July 20, 2026 (SPL set b31d1308-28c3-43f4-e0a6-2f3ed76b8975), via openFDA
Source: FDA drug label (Meperidine Hydrochloride), EPIC PHARMA, LLC, effective November 29, 2025 (SPL set fae5cc34-5917-4445-9516-25f97ffca8db), via openFDA; the full label on DailyMed
What does the phenytoin label say about meperidine?
Phenytoin's label (effective October 15, 2024) and its 1 other brand-application label do not name meperidine 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
| Meperidine | Phenytoin | |
|---|---|---|
| Labeled for | Pain | Seizures and epilepsy |
| Boxed warning | Yes | No |
| Pharmacy cost (NADAC) | $0.157 per mL 50 mg/5 mL solution | $0.145 per capsule 100 mg capsule |
| Shortage now | Listed; available | 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