HYDANTOINS

(Methion, Phenytoin, diphenylhy- dantoin) Phenytoin is not a C.N.S. depressant; some sedation occurs at therapeutic doses but this does not increase with dose-toxic doses produce exctement. Its most outstanding action is abolition of tonic phase of maximal electro shock seizures, with no effect/prolongation of clonic phase. It limits spread of seizure activity. Its stabilizing action on cell membrane confers efficacy in trigeminal neuralgia and cardiac arrhythmias. Phenytoin, in contrast to phenobarbitone, does not interfere with kindling, hence it is less effective in preventing post head injury epilepsy.

Indications

Grandmal, cortica focal and psychomotor epilepsy. Migraine. Trigeminal neuralgia, cardiac arrhythmias (specially digitalis induced)

Dosage

100 mg 2-3 times daily with or after meals. Max. dose : 600 mg daily. Children 4-7 mg/kg bodywt. in divided doses. Max. 300 mg daily.

Contra-Indications

A V Block.

Special Precautions

Monitor ECG during therapy, may inhibit insulin release. Hepatic impairment. Drug should be withdrawn gradually. Haemopoietic complications. Paediatrics: Reduced dose necessary. May cause hyperplesia of gums and hirsutism. Pregnancy: May cause the foetal hydantoin syndrome. Advise folate supplements to mother. Lactation: Drug passes into breast milk. Elderly: Reduced dose may be necessary.

Side Effects

Gum hypertrophy, hirsutism (troublesome in young girls) and acne. Rashes, DLE, lymphadenopathy, neutropenia, megaloblastic anaemia, osteomalacia, hyper glycaemia. Cerebellar and vestibular manifestations, ataxia, vertigo, diplopia, nystagmus,drowsiness, nausea,vomiting, fall in B.P.

Drug Interactions

Anticoagulant effect of warfarin may be altered. May reduce the effectiveness of oral contraceptives. Ethosuximide increases its plasma levels. Chloramphenicol increases the serum phenytoin levels causing toxicity. Rifampicin decreases the serum phenytoin levels. Cyclosporine levels in the blood may be reduced.