Anti Epileptic Flashcards
Mechanism of phenytoin
Increase brain GABA
Decrease membrane excitability by blocking Na+ channel, reducing Na+ entry (so more polarised) and less ca2+ due to GABA inhibition
Increase refractory period due to decreased K influx, hyperpolarisation
Phenytoin follows zero order kinetics when
Concentration exceeds TCR, liver enzymes are saturated
Adverse effects of phenytoin
Decreased vitamin d and b12
Neurological sedation
Gum hypertrophy
Hirsutism (hair growth)
Overdose can lead to convulsion and cerebellar ataxia
Hypersensitivity: rashes, bone marrow depression, liver necrosis
Mechanisms of carbamazepine
Increase brain GABA
Decrease membrane excitability (less na and ca influx during action potential)
Hyperpolarisation as less k+ influx during refractory period
Drug drug interactions of carbamazepine
Inducer of drug metabolising enzyme
Side affects of carbamazepine
Drowsiness Diplopia GI upset Nystagmus B12 and d deficiency
Overdose: ataxia, confusion
Hypersensitivity: rashes, bone marrow depression, hepatitis, SJS
Mechanism of action of phenobarbitone
At low dose, Potentiates GABA and increase frequency of opening of channel
At high dose, independent of GABA, prolong channel opening ie increase duration
This can paralyse the cell and lead to death
Drug drug interaction of phenobarbitone
CYP450 inducer
Mechanism of valproate
Inhibit GABA transaminase, inhibiting GABA break down
Increase K+ conductance, hyperpolarising membrane potential
Drug drug interaction of valproate
Highly bound to plasma protein, displaces diazepam from binding proteins. Hence increase free plasma conc of diazepam, making pt feel sleepy
Inhibit metabolism of other anti epileptics,\
Side effects of valproate
Weight gain
GI upset
Hair loss
Sedation
Hypersensitivity: hepatotoxicity, thrombocytopenia
