Anti-epileptics Flashcards
How do VGSC blockers prevent epilepsy?
Bind to sodium channels in depolarisation, prolonging inactivation state, and reducing the likelihood of excessively high frequency action potentials.
Give 3 examples of 3 VGSC blocker anti-epileptics
Phenyotin, Carbamezapine and Lomatrigene
What 3 clinical advantages does lamotrigene have over other VGSC blocker anti-epileptics?
It is safer to use in pregnancy, has less occurrence of CNS ADRs, and can be used to treat absence seizures unlike other VGSC blockers.
What are some ADRs of phenytoin?
Dizziness, ataxia, headache, nystagmus, anxiety, ginigival hyperplasia, hepersensitity rashes, Steven-Johnson Syndrome
What DDIs can phenytoin cause?
Anything metabolised by CYP450 as it is an inducer, Cimetidine, and NSAIDs or other heavily protein bound drugs.
Why does phenytoin in particular need clinical monitoring?
It has non-linear pharmacokinetics.
How can phenytoin be administered?
Oral or IV
How can carbamezapine be administered?
Oral or rectal
What is a contraindication of carbamezapine use?
AV block
What are some ADRs of carbamezapine?
Dizziness, drowsiness, ataxia, motor disturbance, numbness, tingling, BP increases or decreases, rash, hyponatraemia and myelosupression.
Why is carbamezapines half-life variable and how does it change?
Carbamezapine is a strong CYP450 inducer, and it itself is metabolised by carbamezapine, so on giving a second dose it’s half-life decreases from 30 hours to 15 hours.
What DDI interferes with carbamezapine action?
Anti-depressants.
What is a contraindication for lamotrigene?
Liver disease
What are some ADRs of lamotrigene?
Dizziness, ataxia, somnolence and rashes.
What DDIs affect lamotrigene?
It’s levels are decreased in the presence of the OCP, but are increased in the presence of sodium valproate.
How do GABA mediated inhibition enhancers prevent epilepsy?
Raise levels or action of GABA, which itself acts to cause increased chloride post-synaptic influx, raising action potential thresholds in the central nervous system.
How can sodium valproate and benzodiazapines be administered?
Orally and intravenously
What is a contraindication of sodium valproate?
Liver disease.
How does sodium valproate work?
It is a weak inhibitor of GABA inactivation enzymes, it is a weak agonist for GABA synthesis enzymes, and it is a weak VGSC and VGCC blocker.
What are some ADRs of sodium valproate?
Ataxia, tremor, weight gain, and liver dysfunction/failure.
What drugs antagonise sodium valproate action?
Antidepressants and antipsychotics.
What drugs commonly displace or are displaced by sodium valporate from plasma proteins?
Sodium valproate commonly displaces phenytoin and lamotrigene, but is displaced itself by aspirin.
What is the half-life of sodium valproate?
15 hours.
What clinical monitoring is required in sodium valproate?
Liver function tests.
How do benzodiazapines work?
Bind to receptors on GABA receptor/ Cl-channels. It also has positive allosteric effects, whereby increased benzodiazapine binding causes increased GABA binding and vice versa.
What are 3 benzodiazapines and what are they used for?
Diazepam, Lorazepam and Clonazepam. All 3 can be used for treating anxiety disorders. Diazepam and Lorazepam are used in status epilepticus. Clonazepam can be used for absence seizures and short term use.
What is a contraindication of benzodiazapine use?
Respiratory depression
What are ADRs of benzodiazapines?
Sedation, dependance, tolerance, confusion, ataxia, aggression, CNS depression and respiratory depression.
What can sudden withdrawal of benzodiazapines cause?
Seizures
What reverses benzodiazapines, and what are risks of using it?
IV Flumazenil, and in some cases it can cause seizures or arrhythmias.
What anti-epileptics can cause OCP failure?
Phenytoin and carbamezapine
What are some common teratogenic effects of anti-epileptics?
Neural tube defects, neurological dysfunction,learning difficulties, vitamin K deficiancy (leading to cerebral haemorrhage), facial hypoplasia and digital hypoplasia. Benzodiazapines specifically can cause cleft lip and palate.
What drugs are used in status epilepticus?
Intravenous phenytoin and lorzepam.
