Anti-Epileptic Drugs
They are divided into 3 categories, according to whether they block Na+, Ca2+ or boost GABA receptors.
Na+ channel antagonists:
These agents block sodium channels in the CNS by binding and prolonging inactivated state of channel
– Their action is use dependent, so only active during seizures characterized by excessive neural activity
– They have teratogenic potential and so should be reduced or stopped during pregnancy.
Phenytoin
This has a low therapeutic index with many adverse side effects
Side effects
- These can be remembered with the acronym PHENYTOIN:
– P450 enzyme inducer
– Hirsutism
– Enlarged gums (most common side effect)
– Nystagmus
– Yellow browning of skin
– Teratogenicity ➔ leads to foetal hydantoin syndrome (cleft lip/palate, microcephaly)
– Osteomalacia ➔ Leads to excessive Vitamin D metabolism
– Interference with B12 ➔ Anaemia
– Neuropathy
Carbamazepine
This is the drug of choice for treating trigeminal neuralgia and partial seizures
Side effects
- These can be remembered with the acronym CARBA-MEAN
– Confusion
– Ataxia
– Rashes (Stevens-Johnson Syndrome)
– Blurring of vision
– Agranulocytosis
– Marrow suppression
– Enzyme (P450 inducer)
– ADH release (causes SIADH)
– Neural tube defects (can worsen absence/myoclonic seizures)
Valproic Acid
This is a Na+ channel antagonist that helps to increase GABA activity
Side effects
- These can be remembered with the acronym VALPROATE
– Vomiting
– Appetite up
– Liver toxicity
– Pancreatitis
– Retention of weight
– Oedema
– Alopecia
– Teratogenic (NTDs)
– Enzyme (P450) inhibitor
Lamotrigine+Topiramate+Levetiracetam(Cepra)
These are more examples of sodium channel blockers which have anti-epileptic activity.
Side effects
- Lamotrigine is associated with Stevens-Johnson syndrome
- Levetiracetam can lead to depression and suicidal thoughts
Ca2+ Channel antagonists
e.g. Ethosuximide
It is the drug of choice in absence seizures, which selectively inhibits T-type calcium channels
Benzodiazepines/Phenobarbital
These are the first choice for status epilepticus
ANTI-MIGRAINE DRUGS
In migraine, there is an increase in cerebral activity which releases 5-HT.
– It activates the endothelium by binding 5-HT2 receptors causing vasodilation + sensitizing nerve endings
– 5-HT1D/1B activation inhibits this vasodilation and inflammation of meninges
Triptans
e.g. Sumatriptan, Naratriptan
These are 5-HT1D/1B agonists which cause vasoconstriction, used to treat acute attacks of migraine
– They are most effective if given at the start of the headache, instead of when the aura begins.
Side effects
- “Triptan sensations” – tingling, heat, tightness, pressure symptoms
- Coronary vasospasm so not used in patients with CAD or cerebrovascular disease
Methysurgide/Pizotifen
5-HT2 receptor antagonists which is used in the prophylaxis of migraine
Side effects
- Methysurgide causes retroperitoneal fibrosis so rarely used
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