442-MT2-Antiepileptics

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Author:
jgiantess
ID:
142167
Filename:
442-MT2-Antiepileptics
Updated:
2012-03-19 02:11:52
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pharmacology
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pharmacology
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  1. phenobarbital
    • 1) GABA-A receptor allosteric modulator: enhance GABA-mediated pre-syn & post-syn inhibition
    • 2) block release of glutamate from pre-syn terminals (axo-axonic)
    • - partial & tonic-clonic seizures
    • - long action, t1/2 100 hours
    • - CYP2C and CYP3A enzyme inducer: alters metab of many drugs (e.g. oral contraceptives)
    • - VPA increases phenobarb levels
    • - SE: sedation (w/ tolerance), nystagmus & ataxia (higher doses), hyperactivity in kids, confusion in elderly.
  2. primodone
    • - active metabolite is phenobarb, but primodone also active.
    • - use similar, but used as adjunct
    • - SE: blood dyscrasias more likely
  3. phenytoin (Dilantin)
    • 1) Na+ channel blocker: increase refractory period,decrease ability to generate high f Na+ spikes (stabilizes neuronal membrane, decreases NT release, focal firing, and sz spread.)
    • - partial, tonic-clonic, status epilepticus.
    • - NOT effective in absence or myoclonic: may worsen
    • - saturable metabolism, t1/2 20-60hours
    • - Topiramate enzyme inhib (increase PHT), CBZ, VGB enzyme inducers (reduce PHT), and vice versa.
    • - pregnancy increases metabolism, so dose must be adjusted before and after delivery
    • - SE: nystagmus, ataxia, slurred speech, confusion, tremor, gingival hyperplasia, skin rash/acne, hirsutism, coarsened facial features
  4. carbamazepine (Tegretol) for epilepsy
    • 1) Na+ channel blocker: increase refractory period,decrease ability to generate high f Na+ spikes (stabilizes neuronal membrane, decreases NT release, focal firing, and sz spread.)
    • 2) Alleyne: also GABA-a receptor allosteric modulator (inc. membrane hyperpol & sz threshold, dec. focal firing, aggravate spike-wave discharges)
    • - complex partial & tonic-clonic, also for trigeminal neuralgia
    • - may worsen absence & myoclonic
    • - slow and variable absorption, t1/2 10-20 hours
    • - induces enzymes (decrease clobazam, VPA)
    • - SE: drowsiness, ataxia, seizures at high doses, diplopia, transient leukopenia
  5. valproic acid (Depakene)
    • 1) GABA-T blocker / stimulator of glutamic acid decarboxylase to synthesize GABA
    • 2) Na+ channel blocker: blocks high f Na+ spikes
    • 3) T-type Ca2+ channel blocker: decrease oscillation of cortical-projecting thalamic neurons
    • - broad spec: partial, tonic-clonic, absence
    • - inhibits drug metabolizing enzymes, and increases phenobarb levels
    • - SE: GI disturbances, sedation, transient hair loss
    • - toxicity: hepatotoxicity(rare) in kids 2 years old, pancreatitis
  6. ethosuximide (Zarontin)
    • 1) T-type Ca2+ channel blocker
    • - absence seizures
    • - SE: GI disturbances, sedation, dizziness, headache
    • - methsuximide is similar but less effective
  7. benzodiazepines
    • 1) GABA-A receptor allosteric modulator: enhance GABA-mediated pre-syn & post-syn inhibition
    • 2) block release of glutamate from pre-syn terminals (axo-axonic)
    • - DOC for arresting status epilepticus (lorazepam, diazepam)...IV for fast effects.
    • - otherwise, not effective for most seizures...tolerance rapid.
    • - used mainly in adjunctive therapy
  8. gabapentin (Neurontin) for epilepsy
    • 1) Na+ channel blocker (high f)
    • 2) may release GABA from glial cells
    • 3) Alleyne: act as alpha-2-gamma ligands to modulate NT release
    • - appear not to have GABA agonist activity.
    • - adjunctive therapy with partial or tonic-clonic seizures, also useful in chronic pain syndromes
    • - *is not PPB, and not metab'd by liver (not induce/inhibit metab of other drugs)
    • - well-tol'd (sedation, dizziness, fatigue, ataxia)
  9. vigabatrin (Sabril)
    • 1) GABA-T irreversible inhibitor (inc. extrasynaptic GABA & membrane hyperpol, dec. focal firing, aggravate spike-wave discharges.)
    • - (gabapentin-like) adjunctive therapy with partial or tonic-clonic seizures, also useful in chronic pain syndromes
    • - *is not PPB, and is excreted unchanged in urine & not metab'd by liver (not induce/inhibit metab of other drugs)
    • - well-tol'd (sedation, dizziness, fatigue)
    • - retinal degeneration
  10. lamotrigine (Lamictal) for epilepsy
    • 1) Na+ channel blocker
    • 2) Glutamate presynaptic release inhibitor, MoA not understood
    • 3) Alleyne: Ca2+ channel blocker
    • 4) Alleyne: enhancer of HCN (hyperpol-activated cyclic nucleotide-gated channels) activity -> bugger large hyperpol + depol inputs
    • - broad spec: partial, absence, tonic-clonic
    • - DI: PHT, CBZ increase metab while VPA reduce elimination
    • - SE: sedation, dizziness, fatigue, ataxia...severe derm reactions in children
  11. topiramate (Topamax) for epilepsy
    • 1) GABA receptor allosteric modulator: enhance GABA-mediated pre-syn & post-syn inhibition
    • 2) Na+ channel blocker
    • 3) AMPA blocker: decreased postsynaptic excitability of target neuron: block PDS
    • - broad spec: partial, absence, tonic-clonic
    • - SE: sedation, dizziness, fatigue, ataxia
    • - excreted unchanged in urine
  12. tiagabine (Gabatril)
    • 1) GABA neuronal uptake blocker
    • - adjunct for partial, tonic-clonic seizures
    • - metabolized by CYP3A - Drug Interactions!
  13. felbamate (Felbatol...not avail in Canada)
    • 1) Na+ channel blocker
    • 2) Glycine recognition site blocker @ NMDA receptor: prevents enhancement of NMDA actions
    • 3) Alleyne: enhance GABA actions
    • - broad spec: partial, tonic-clonic, absence
    • - excreted unchanged in urine
    • - may produce aplastic anemia and hepatic failure
  14. zonisamide (Zonegran...not avail in Canada) for epilepsy
    • 1) Na+ channel blocker
    • 2) T-type Ca2+ channel blocker
    • 3) Alleyne: brain carbonic anhydrase inhibitor (inc. HCN-med'd currents, dec. NMDA-med'd currents, inc. GABA-med'd inhibition)
    • - adjunctive therapy for partial or tonic-clonic
    • - well absorbed - 85% of oral dose is excreted in urine un-metabolized
    • - PHT, CBZ decrease, LTG increase levels of zonisamide
    • - well-tol'd (sedation, dizziness, fatigue, ataxia)
    • - may produce renal calculi (via inhibition of carbonic anhydrase)

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