Question 1

What is Phenytoin used for?

Accepted Answer

Phenytoin is indicated for: Epilepsy (historical use), Status epilepticus (alternative to diazepam).

Question 2

What routes can Phenytoin be administered by?

Accepted Answer

Available routes: PO, IV.

Question 3

Which species have cited Phenytoin dosing data?

Accepted Answer

Phenytoin dosing in the ExoticRx formulary covers 1 species: Dog (Domestic).

Question 4

Is Phenytoin a controlled substance?

Accepted Answer

Phenytoin is not federally scheduled as a controlled substance, but is veterinary prescription only in most jurisdictions.

Question 5

What are the warnings or contraindications for Phenytoin?

Accepted Answer

Hepatotoxicity in dogs with chronic use. Rapid hepatic metabolism in dogs limits usefulness. Zero-order kinetics make dosing unpredictable. Gingival hyperplasia. Generally not recommended in dogs — phenobarbital preferred.

Question 6

What are the side effects of Phenytoin?

Accepted Answer

Reported side effects, adverse reactions, and contraindications for Phenytoin: Hepatotoxicity in dogs with chronic use. Rapid hepatic metabolism in dogs limits usefulness. Zero-order kinetics make dosing unpredictable. Gingival hyperplasia. Generally not recommended in dogs — phenobarbital preferred.

Question 7

How does Phenytoin work?

Accepted Answer

Stabilizes neuronal membranes by blocking voltage-dependent sodium channels in their inactive state, preventing repetitive firing. Does not affect normal neuronal activity.

Species	Route	Dose	Frequency	Evidence	Source
Dog (Domestic)	PO	15–40 mg/kg	q8h	Moderate	Plumb's Veterinary Drug Handbook, 9th Ed
Dog (Domestic)	IV	10–15 mg/kg	Slow IV push over 5-10 min	Moderate	Plumb's Veterinary Drug Handbook, 9th Ed

Phenytoin

Drug Class

Routes

Indications

Mechanism of Action

Side effects & warnings

Species with Phenytoin dosing data (2 dose rules)

Evidence levels across 2 dose rules

Backed by a published source

Sample dosing (2 of 2 cited rules)

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