Anticonvulsants Flashcards
Name 3 mechanisms of actions of anticonvulsants
- prolong inactivated state of voltage gated Na and Ca channels presynaptically: reduce likelihood repetitive action potentials, reduce necerotransmitter release, prevent seizure spread
- enhance effects of GABA (inhibitory) via GABA - A receptor complex:open ligand gated Cl channels causing suppression of discharges
- inhibit effects of excitatory neurotransmitter, glutamate, via NMDA receptor (and ampa R): prevent opening ligand gated Na and Ca channels
Name the 4 sites on the gaba-a r complex
• GABA site • Benzo • barbiturate • alcohol (All neuroinhibitory) 4 bs All very addictive.
Name 5 anticonvulsants that prolong the inactivated state of voltage dependent Na and Ca channels
- Phenytoin
- carbamazepine
- valproate
- oxcarbazepine
- lamotrigine
- topiramate
- gabapentin
Name 3 anticonvulsants that inhibit effects of excitatory neurotransmitter glutamate by modulating NMDA (and ampa) receptors (nmda antagonists)
• Topiramate • magnesium • felbamate Zonisamide (Lamotrigine) (Ketamine)
Name 3 classes anticonvulsants with examples that enhance effects of inhibitory neurotransmitter GABA
• GABA site (inhibit GABA transaminase irreversibly): vigabatrin
• benzodiazepines (bind at GABA A r site): diazepam, clonazepam
• barbiturates: phenobarbitone
(GABA agonists: gabapentin)
Name an important side effect of phenytoin and carbamazepine Due to their action on CYP 450
Inducers
Vit D hypermetabolised causing osteopenia.
Name 3 indications phenytoin
Generalised and partial seizures, status epilepticus
Name 2 important pharmacokinetic components of phenytoin
• High protein binding 95% (increased risk toxicity if displaced)
• liver metabolism saturable: zero order kinetics (small increase dose may cause unpredictable increase in Cp with toxicity)
Old drug, so risks toxicity high
Name 5 important adverse effects phenytoin
- CNS: cerebellar syndrome, sedation
- allergic effects with cross sensitivity to carbamazepine: rash, hepatitis
- skin and collagen: gum hypertrophy, coarsening of facial features, hirsutism
- haem: megaloblastic anemia
- teratogenic: malformations
Name 5 indications carbamazepine
• Partial seizures
• generalised seizures, excluding absence and atonic
Other
• mood stabiliser bipolar disorder prophylaxis
• trigeminal neuralgia and other chronic pain syndromes
• chronic dystonic disorders
• intractable hiccups , neurohypophyseal diabetes insipidus
Name 5 adverse effects carbamazepine
• Ataxia • nystagmus • dysarthria • vertigo • sedation Common but not severe, occur when levels > 8,5 mg/l
Name 2 drug interactions carbamazepine
- Maoi: contraindicated
* CYP450 inducer: reduce efficacy warfarin, theophylline, oc, other anticonvulsants
Name 2 indications phenobarbitone
Barbiturates
• generalised and partial seizures
Second line! Too sedative in adults, behavioural disturbances in children, very addictive
Name 2 indications sodium valproate
Partial and generalised epilepsy
First line
Juvenile myoclonic epilepsy
Name 3 adverse effects sodium valproate
• git • liver failure and hepatic necrosis, rare. • pancreatitis • Hair loss - Teratogen:ntd
Indication ethosuxamide?
Drug of choice for absence seizures children
Not others seizures, may make them worse
Indication gabapentin?
- Add on for absence seizures
* partial and generalised epilepsy monotherapy
Gabapentin AE?
Somnolence
Lamotrigine indications? (3)
- Partial seizures
- generalised
- absence
Contraindication lamotrigine?
Liver or renal failure
Lamotrigine adverse effects (2)
• Hypersensitivity rashes: Steven’s Johnsons, toxic epidermal necrolysis, angioedema
• flu-like symptoms
Rare
Name 2 indications topirimate
Generalised and partial seizures
Newer drug
Name 5 adverse effects topirimate
- Poor concentration and memory
- Impaired speech
- ataxia
- somnolence
- anorexia and taste perversion
- syndrome of acute myopia associated with secondary closed angle glaucoma
Vigabatrin indication
Last resort for epilepsy due to significant irreversible visual defects
