PHENYTOIN SODIUM vs PRIMIDONE

Independent side-by-side comparison.

Rated against independent regulatory sources·Last updated August 21, 2026·How we rate

Possible drug interaction. PHENYTOIN SODIUM and PRIMIDONE are different prescription medicines. Combining or switching between them can cause interactions — talk to a pharmacist or prescriber before making changes. This page is not medical advice.

Attribute	PHENYTOIN SODIUM	PRIMIDONE
Rating	New	70/100
Pharmacy pays	$0.18 /mL	~$2.89 /30
Type	RX	RX
Active ingredient	PHENYTOIN SODIUM	PRIMIDONE
Manufacturer	Marsam Pharms LLC	Amneal
Dosage forms	Capsule, Injectable	Tablet
Drug class	Anti-Epileptic Agent	Anti-Epileptic Agent
Boxed warning	None	None
Half-life	About 22 hours on average, ranging from 7 to 42 hours — but phenytoin does NOT have a single fixed half-life. It follows nonlinear, saturable (Michaelis-Menten) kinetics, so the half-life lengthens as the dose and blood level rise; the label warns that "small incremental doses may increase the half-life and produce very substantial increases in serum levels" once levels are in the upper range.	—
Treats	Tonic-Clonic Epilepsy, Temporal Lobe Epilepsy, Status Epilepticus	Partial Epilepsies, Tonic-Clonic Epilepsy, Tremor

phenytoin sodium primidone

Rating

New

70/100

Pharmacy pays

$0.18 /mL

~$2.89 /30

Type

Active ingredient

PHENYTOIN SODIUM

PRIMIDONE

Manufacturer

Marsam Pharms LLC

Amneal

Dosage forms

Capsule, Injectable

Tablet

Drug class

Anti-Epileptic Agent

Boxed warning

None

Half-life

About 22 hours on average, ranging from 7 to 42 hours — but phenytoin does NOT have a single fixed half-life. It follows nonlinear, saturable (Michaelis-Menten) kinetics, so the half-life lengthens as the dose and blood level rise; the label warns that "small incremental doses may increase the half-life and produce very substantial increases in serum levels" once levels are in the upper range.

—

Treats

Tonic-Clonic Epilepsy, Temporal Lobe Epilepsy, Status Epilepticus

Partial Epilepsies, Tonic-Clonic Epilepsy, Tremor

Frequently asked questions

What is the difference between Phenytoin Sodium and Primidone?

Phenytoin Sodium contains Phenytoin Sodium, while Primidone contains Primidone — they have different active ingredients.

Ratings are based on FDA regulatory (recall-safety) data. This comparison is for general reference only — not medical advice. Always consult a licensed professional before choosing or switching a medication.