Doses - PHENYTOIN SODIUM

Dogs:

For treatment of seizures:
a) 15 - 40 mg/kg PO tid (Morgan 1988)
b) 20 - 35 mg/kg tid (Bunch 1986)
c) Initially, 8.8 - 17.6 mg/kg PO in divided doses, then gradually increase or decrease doseto maintain control. May take several days for seizure control to be attained. (Packageinsert; Dilantin® Veterinary ¯ Parke-Davis)
Author's note: Because of the extremely fast half-life of phenytoin in dogs, it is unlikelythat this dosage regimen ("c") will attain serum levels of 10 - 20 micrograms/ml whichare thought to be necessary for adequate seizure control.
For treatment of ventricular arrhythmias:
a) Up to 10 mg/kg IV in increments of 2 - 4 mg/kg or 20 - 35 mg/kg PO tid (Moses 1988)
b) 10 mg/kg IV q8h or 30 mg/kg PO q8h (Wilcke 1985)
For treatment of hypoglycemia secondary to tumor:
a) 6 mg/kg PO bid-tid (Morgan 1988)
Cats: Note: Because cats can easily accumulate this drug and develop symptoms of toxicity, theuse of phenytoin is very controversial in this species. Diligent monitoring is required.
For treatment of ventricular arrhythmias:
a) 2 - 3 mg/kg PO q24h (Wilcke 1985)
For treatment of seizures:
a) 2 - 3 mg/kg daily PO; 20 mg/kg per week (Bunch 1986)

Horses:

For seizures:
a) 2.83 - 16.43 mg/kg PO q8h to obtain serum levels from 5 - 10 micrograms/ml. Suggestmonitoring serum levels to adjust dosage. (Kowalczyk and Beech 1983)
Monitoring Parameters -

1) Level of seizure control; sedation/ataxia

2) Body weight (anorexia)

3) Liver enzymes (if chronic therapy) & serum albumin

4) Serum drug levels if signs of toxicity or lack of seizure control
Client Information - Notify veterinarian if dog becomes anorexic, lethargic, ataxic, or if seizuresare not adequately controlled. The importance of regular dosing is imperative for successfultherapy.
Dosage Forms/Preparations - Veterinary-Approved Products:
Extended Phenytoin Sodium Capsules, USP® (Fort Dodge) (Rx) 100 mg tablets. Approved foruse in dogs.Note: This product may no longer be marketed.

Human-Approved Products:

Phenytoin Sodium, Extended Oral Capsules 30 mg, 100 mg; Dilantin® Kapseals® (Parke-Davis); generic, (Rx)
Phenytoin Oral Suspension 25 mg/ml in 8 oz. bottles; Dilantin-125® (Parke-Davis) (Rx)Phenytoin Oral Tablets 50 mg; Dilantin® Infa-Tabs® (Parke-Davis) (Rx)
Phenytoin Sodium for Injection 50 mg/ml (46 mg/ml phenytoin) in 2 ml and 5 ml amps, syringes and vials; 150 mg (100 mg phenytoin sodium) in 2 ml vials; 750 mg (500 mg phenytoinsodium) in 10 ml vials (Rx)
Phenytoin may also be called diphenylhydantoin or DPH.