Anti- Epileptics Flashcards
Define epilepsy
Episodic discharge or abnormal high frequency electrical activity in the brain leading to seizure
Describe the 2 types of focal seizures (only a certain focal area is affected)
Simple - remain conscious
Complex - impaired consciousness
Symptoms reflect area affected
Describe the 2 types of generalised seizures
Tonic clonic - unconscious, stiffening of the limbs, jerking of the limbs
Absence - as if daydreaming but can’t respond
What are some of the signs of partial seizures?
Unusual feeling, unusual taste, unusual smell, tingling, twitching, smacking lips, random noises, picking at clothes
Describe some signs of generalised seizures
Vacant stare (absence)
Incontinence, cyanosis, tongue biting
What is status epilepticus?
Seizure lasting over 30 mins/multiple back to back (>5 mins an emergency)
Risk of hypoxia due to changes in breathing and heart rhythm, brain damage and SUDEP
What are the 2 classes of anti epileptics?
Voltage gated Na blockers
Enhancing GABA inhibition
How do Na channel blockers work?
They bind to the channel once it has been inactivated and keep it in this state meaning Na can not enter the cell to cause depolarisation thus reduces the probability of an action potential. It dissociates once the membrane potential is back to normal
How do GABA agonists work?
GABA is an inhibitory neurotransmitter that reduces excitability. GABA agonists bind with the GABAA receptor (ligand gated ion channel) which increases Cl conductance causing hyperpolarisation.
Reuptake of GABA can also be targeted
Name 3 Na channel blockers
Carbamazepine
Phenytoin
Lamotragine
Name the 2 GABA agonists
Benzodiazepines e.g. Diazepam, lorazepam
Valproate
Describe the pharmacokinetics of carbamazepine
Protein bound
Half life of 30 hours but induces own metabolism with CYP450 so reduces half life to 15 hours
What are the main ADRs associated with Na blockers?
Dizziness, ataxia
Carbamazepine - numbness, vomiting, hyponatraemic rash
Lamotrigine - nausea, hyponatraemic rash
Phenytoin - Steven Johnson syndrome, gingervival hyperplasia
What are the major DDIs with carbamezipine?
CYP450 inducers - warfarin, oral contraceptive, corticosteroids
Antidepressants
Describe the pharmacokinetics for phenytoin
Protein bound, non linear, variable half life, requires monitoring
What are the main DDIs for phenytoin?
Induces CYP450 - contraceptive pill
Protein binding by valproate and salicylate exacerbates non linear kinetics
Cimetidine increases
Describe the pharmacokinetics of lamotrigine
Linear, half life of 24 hours protein bound
What are the main DDIs for lamotrigine?
Is not a CYP450 inducer
Contraceptive pill reduces levels
Valproate increases levels
Describe the pharmacokinetics of benzodiazepines
Linear, half life varies, protein bound
What are the main ADRs of benzodiazepines?
Sedation, confusion, impaired coordination, CNS depression, respiratory depression, tolerance, dependence
What are the main ADRs for valproate?
Ataxia, tremor, sedation, liver failure (requires monitoring)
What are the main DDIs for valproate?
Protein binding affects other AED concentrations
Antipsychotics/antidepressants antagonise so lower threshold
Aspirin increases action
Which AEDs reduce efficacy of the contraceptive pill?
Carbamazepine, phenytoin
Which AED is especially teratogenic?
Valproate (neural the defect)
Which AED is the safest in pregnancy?
Lamotrigine
Which AED is first line in pregnant women?
Lamotrigine
Which AED is first line for partial seizures?
Carbamazepine
Which AED is first line for generalised seizures?
Valproate
How would you manage status epilepticus?
Benzodiazepines/phenytoin
ITU - sedation, paralysis, ventilation
Exclude hypoglycaemia
