Phenytoin is effective in tonic-clonic and partial seizures. It can have a low therapeutic index in some indications and needs to be titrated in small increments due to its pharmacokinetics.
Although the drug was first synthesised by a physician in 1908 its accepted major clinical indication was not discovered until 1938. It is being replaced by anti-epileptic drugs with better clinical profiles as first line therapy.Phenytoin is not usually prescribed as a generic, in case of variations in bio-availability.
Mechanism of action
It blocks neuronal sodium channels but may have other mechanisms of action.
The main catch is that the drug exhibits saturation kinetics in which a small increment of dose of the order of 25mg in an adult can in some patients move from the therapeutic dose to a toxic dose. The drug has a fair 'half-life' so can be administered once a day (given its zero-order pharmacokinetics, the concept of a half-life, strictly speaking, doesn't apply).
It can be given orally or iv. Dosing should generally (in non emergency situations) be based upon monitoring for clinical effectiveness with titration by small increments based on plasma blood levels. Typical healthy adult adult oral doses are about 200mg to 500mg a day and usual practice in adults is to titrate upwards from the lower end of this range.
- ↑ Pharma firm hikes cost of epilepsy drug 24 times http://www.telegraph.co.uk/health/healthnews/9604683/Pharma-firm-hikes-cost-of-epilepsy-drug-24-times.html