4. Pharmaco Flashcards
Seizure
a paroxysmal (unexpected) event due to abnormal, hypersynchronous discharge from a mass of CNS neurons
manifestation of seizure
Diverse manifestation: convulsion (observable) to an experience (subjective)
is a single seizure due to correctable or avoidable circumstance (ie provoked) considered an epilepsy?
not an epilepsy (eg due to alcohol, hypoglycaemia, pyrexia, sleep deprivation)
epilepsy pathophysiology
a seizure occurs when there is excessive synchronous depolarisation due to unbalanced excitatory and inhibitory receptor/ ion channel function which favours depolarisation → dysregulated/ unregulated discharge
types of seziure
- generalised (both hemisphere affected, consciousness affected) -> tonic clonic, absence
- partial seizures (half hemisphere affected) -> simple (consciousness not impaired), complex (consciousness impaired)
- status epilepticus
rationale for anti-epileptics
- decrease membrane excitability by altering Na+ and Ca2+ conductance during action potential
- enhanced effects of inhibitory GABA NT (GABA when bind to receptor opens Cl- channels allowing Cl- ions to enter)
- drugs should be individualised and started on monotherapy initially
phenytoin MOA
block voltage-dependent Na+ channels → decreases Na+ entry → decrease AP discharge → decrease excitation of neuron
phenytoin indication
for all types of seizures except absence seizures
characteristics of phenytoin
- relative narrow therapeutic range
- teratogenic
- non-linear saturation kinetics profile (need TDM)
MOA of carbamazepine
blockade of voltage-dependent Na+ channels (similar to phenytoin)
Indiction of carbamazepine
for all types of seizures except absence seizures
characteristics of carbamazepine
Autoinduction: hepatic CYP450 enzyme inducer, T1/2 shortens with repeated/increasing doses → accelerate metabolism of carbamazepine and other drugs
carbamazepine pgx
HLA-B*1502 positive - increased risk of SJS/ TEN (require PGx testing before drug initiation)
MOA of valproate
- blockade of voltage-dependent Na+ and Ca2+ channels
- inhibit GABA transaminase (enzyme that breakdown GABA) → increase GABA (inhibitory NT)
indication for valproate
for all types of seizures including absence seizures
characteristics of valproate
strongly bound to plasma proteins, displaces other antiepileptics/ drugs (ie DDI)
Adverse effects of antiepileptics (dose related)
drowsiness, confusion, nystagmus (shifty eyes), ataxia (unable to keep balance), slurred speech, nausea, unusual behaviour, mental changes, coma
Adverse effects of antiepileptics (non dose related)
hirsutism, acne, gingival hyperplasia (swollen gums), folate deficiency, osteomalacia (softening of bone), hypersensitivity (eg SJS)
MOA of benzodiazepines
bind to regulatory site of of GABA receptors (different binding site from GABA) → increase GABA mediated Cl- ions influx → hyperpolarisation → neurons not firing
- potentiates inhibitory effect of GABA (only works when GABA is present)
acute toxicity/overdose of benzodiazepines
acute toxicity/ overdose - cause severe respiratory depression, especially when used concurrently with alcohol
tx of benzodiazepine overdose
flumazenil (benzodiazepine competitive antagonist)