DILANTIN

What it is

DILANTIN is phenytoin sodium in capsule form and phenytoin in chewable tablet and oral suspension formulations. The capsules are available in 30 mg and 100 mg strengths. Chewable tablets (INFATABS) contain 50 mg phenytoin. The paediatric suspension contains 30 mg phenytoin per 5 mL.

Approved indications

— Generalised tonic-clonic (grand mal) seizures — Psychomotor seizures — Prevention of seizures occurring during or after neurosurgery

Dosing overview

Adult therapy is initiated with 4 to 5 mg/kg/day in 2 to 3 divided doses, with further upward adjustment possible to a maximum of 600 mg/day at approximately 2 week intervals. Paediatric therapy is initiated with 5 mg/kg/day in 2 to 3 equally divided doses not exceeding 300 mg daily, with recommended maintenance dosage of 4 to 8 mg/kg daily. Serum levels between 10 µg/mL and 20 µg/mL are considered clinically effective. Elderly patients may require lower or less frequent dosing due to decreased phenytoin clearance.

Key safety warnings

Antiepileptic drugs including phenytoin increase the risk of suicidal thoughts or behaviour in patients taking these drugs for any indication, and patients should be monitored for the emergence or worsening of depression, suicidal thoughts or behaviour, and unusual changes in mood or behaviour. Phenytoin can cause rare, severe cutaneous adverse reactions such as acute generalised exanthematous pustulosis, exfoliative dermatitis, Stevens-Johnson syndrome, toxic epidermal necrolysis, and drug reaction with eosinophilia and systemic symptoms, which can be fatal. The risk of serious skin reactions and other hypersensitivity reactions may be higher in black patients. Hypersensitivity syndrome or drug reaction with eosinophilia and systemic symptoms has been reported in patients taking phenytoin, and some of these events have been fatal or life threatening. Toxic hepatitis, liver damage and acute hepatotoxicity including acute hepatic failure have been reported with phenytoin. Haematopoietic complications, some fatal, have occasionally been reported and have included thrombocytopenia, leucopenia, granulocytopenia, agranulocytosis, and pancytopenia. Cases of bradycardia and asystole/cardiac arrest have been reported, most commonly in association with phenytoin toxicity, but also at recommended phenytoin doses and levels. Phenytoin may cause fetal harm when administered to a pregnant woman, and prenatal exposure may increase the risks for congenital malformations and other adverse development outcomes.

Contraindications

Phenytoin is contraindicated in patients with a history of hypersensitivity to phenytoin, other hydantoin products, or other inactive ingredients in this product. Co-administration with delavirdine is contraindicated due to the potential for loss of virologic response and possible resistance to delavirdine or to the class of non-nucleoside reverse transcriptase inhibitors.

PBS listing

Phenytoin sodium 30 mg capsules are listed on the PBS with a restriction and ex-manufacturer price of A$36.80. Phenytoin sodium 100 mg capsules are listed on the PBS with a restriction and ex-manufacturer price of A$18.90. Phenytoin 50 mg tablets are listed on the PBS with a restriction and ex-manufacturer price of A$48.53. The oral suspension 30 mg per 5 mL (500 mL) is listed on the PBS with a restriction and ex-manufacturer price of A$12.20.

Regulatory history

DILANTIN paediatric suspension was first listed on the ARTG on 20 September 1991. DILANTIN 30 mg and 100 mg capsules were first listed on the ARTG on 11 December 2017. DILANTIN INFATABS 50 mg chewable tablets were first listed on the ARTG on 31 July 2018.