Two medicines, side by side
Phenytoin vs gabapentin
Phenytoin and gabapentin are both labeled for seizures and epilepsy. Drugs@FDA records approvals of phenytoin since 1953 and of gabapentin since 1993. Pharmacies paid $0.145 per phenytoin sod ext 100 mg capsule and $0.0218 per gabapentin 100 mg capsule (NADAC, October 7, 2026). How each works, in its label's words: Phenytoin, “The precise mechanism by which phenytoin exerts its therapeutic effect has not been established but is thought to involve the voltage-dependent blockade of membrane sodium channels resulting in a …”; Gabapentin, “The precise mechanisms by which gabapentin produces its analgesic and antiepileptic actions are unknown.”
Check it at the source: the phenytoin FDA label on DailyMed (effective October 15, 2024); the gabapentin FDA label on DailyMed (effective May 12, 2026).
Highlights of the phenytoin record
Phenytoin (Dilantin) · label of October 15, 2024
Used for
From the label: indicationsPHENYTEK ® capsules (extended phenytoin sodium capsules) are indicated for the treatment of tonic-clonic (grand mal) and psychomotor (temporal lobe) seizures and prevention and treatment of seizures occurring during or following neurosurgery. […]
On the market
- Earliest approval on file
- January 6, 1953
- Generic labelers
- 29 labelers
- Pharmacy cost
- $0.145 per capsule
Supply and safety
- Shortage
- No current entry
- Recalls
- 11
Highlights of the gabapentin record
Gabapentin (Neurontin) · label of May 12, 2026
Used for
From the label: indicationsNEURONTIN ® is indicated for: • Management of postherpetic neuralgia in adults • Adjunctive therapy in the treatment of partial onset seizures, with and without secondary generalization, in adults and pediatric patients 3 years and older with epilepsy NEURONTIN is indicated for: • Postherpetic neuralgia in adults ( 1 ) • Adjunctive therapy in the treatment of partial onset seizures, with and without secondary generalization, in adults and pediatric patients 3 years and older with epilepsy […]
On the market
- Earliest approval on file
- December 30, 1993
- Generic labelers
- 85 labelers
- Pharmacy cost
- $0.0218 per capsule
Supply and safety
- Shortage
- No current entry
- Recalls
- 22
Source: FDA drug labels via openFDA (Phenytoin label of October 15, 2024, Gabapentin label of May 12, 2026); NDC Directory, Drugs@FDA, NADAC, FDA shortages and recalls (October 8, 2026)
How do phenytoin and gabapentin differ on the record?
How each works, in its label's words: Phenytoin, “The precise mechanism by which phenytoin exerts its therapeutic effect has not been established but is thought to involve the voltage-dependent blockade of membrane sodium channels resulting in a …”; Gabapentin, “The precise mechanisms by which gabapentin produces its analgesic and antiepileptic actions are unknown.”
Both are in FDA's class anti-epileptic agents.
Half-life, in each label's words: Phenytoin, “Elimination The plasma half-life in man after oral administration of phenytoin averages 22 hours, with a range of 7 to …”; Gabapentin, “Gabapentin elimination half-life is 5 to 7 hours and is unaltered by dose or following multiple dosing.”
Generics: phenytoin since 1975; gabapentin since 2003 (Drugs@FDA).
| Phenytoin | Gabapentin | |
|---|---|---|
| Labeled for | Seizures and epilepsy | Nerve pain and fibromyalgia, Seizures and epilepsy |
| Pharmacologic class | Anti-epileptic Agent | Anti-epileptic Agent |
| How it works (label) | The precise mechanism by which phenytoin exerts its therapeutic effect has not been established but is thought to involve the voltage-dependent blockade of membrane sodium channels resulting in a reduction in sustained high-frequency … | The precise mechanisms by which gabapentin produces its analgesic and antiepileptic actions are unknown. |
| Half-life (label) | Elimination The plasma half-life in man after oral administration of phenytoin averages 22 hours, with a range of 7 to 42 hours. | Gabapentin elimination half-life is 5 to 7 hours and is unaltered by dose or following multiple dosing. |
| Earliest approval on file (Drugs@FDA) | January 6, 1953 | December 30, 1993 |
| First generic approved | July 16, 1975 | September 12, 2003 |
| Generic labelers (NDC) | 29 labelers | 85 labelers |
| Pharmacy cost (NADAC, each one's most listed form; strengths differ) | $0.145 per capsule (Phenytoin sod ext 100 mg capsule) | $0.0218 per capsule (Gabapentin 100 mg capsule) |
| 12-month price change | -5% | +0.9% |
| Boxed warning | No | No |
| Shortage now | No current entry | No current entry |
| Recalls recorded | 11 | 22 |
| FAERS reports (a report is not proof of cause; counts follow how widely a medicine is used) | 40,278 | 362,654 |
| DEA schedule | none | none |
Source: Drugs@FDA, FDA NDC Directory, CMS NADAC of October 7, 2026, FDA shortages and recalls, FAERS via openFDA (FDA files October 8, 2026)
Do their labels mention each other?
Gabapentin label, drug interactionsPhenytoin In a single (400 mg) and multiple dose (400 mg three times a day) study of NEURONTIN in epileptic patients (N=8) maintained on phenytoin monotherapy for at least 2 months, gabapentin had no effect on the steady-state trough plasma concentrations of phenytoin and phenytoin had no effect on gabapentin pharmacokinetics.
Gabapentin label, drug interactionsIn a single (400 mg) and multiple dose (400 mg three times daily) study of gabapentin immediate release in epileptic patients (N=8) maintained on phenytoin monotherapy for at least 2 months, gabapentin had no effect on the steady-state trough plasma concentrations of phenytoin and phenytoin had no effect on gabapentin pharmacokinetics.
Source: FDA drug labels via openFDA
What next?
- Alternatives to phenytoin
- every medicine labeled for the same conditions