Phenytoin
From Ganfyd
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.
 | Anti-epileptics are a major cause of drug related malpractice claims. Ensure you have an accurate diagnosis, good understanding of dose titration, monitoring and interactions for a given drug. There is an increased risk of teratogenicity with anti-epileptic drugs. Sudden withdrawal can be dangerous. |
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History
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.
In 2012 the UK after a transfer of the licence for the brand Epanutin from Pfizer to Flynn the price was increased very greatly.[1] The Telegraph reported manufacture continued in the Pfizer plant in Stevenage and that the drug is practically a monopoly.
Mechanism of action
It blocks neuronal sodium channels but may have other mechanisms of action.
Metabolism
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).
Dosing
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.
References
- ↑ 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
