Anticonvulsants Flashcards
carbamazepine
Antiepileptic Drug
- Goal to prevent seizures while minimizing side-effects, by using simplest drug regimen
Mechanism:
- Blocks abnormal voltage-gated channels
- Blocks the Focal Epileptogenesis step in seizure
Alters ionic conductance to suppress firing of action potential:
- Inhibits voltage-activated Na channels to prolong the refractory period and reduce sustained firing
Causes drug interaction of Phenytoin:
- Stimulates Phenytonin Metabolism
Drug of choice for:
- Partial simple
- Partial complex
- Tonic-clonic seziures
- Use in: terminal Neuraliga, bipolar disorder
Oral administration
Slowly absorbed
HIGHLY LIPID SOLUBLE (rapid penetration to brain)
Metabolized by: p450 enzymes
- Induces p450 enzyme to increase it’s own metabolism
(10-15 hrs half life)
Drug Interactions:
- Enhance p450 system so increases metabolism of antiepileptics (phenytoin)
Metabolism is inhibited by several drugs:
- Cimetidine
- Diltiazem
- Erythromycin
- Isoniazid
- Propoxyphene
Can be used with barbiturates for simple partial and tonic-clonic seiaures and febrile seizures in children
Hepatotoxicity
Common Side Effects:
- Drowsiness/sedation
- Ataxia
- Nausea/Vomiting
- Skin rash
- Metabolic changes: weight gain/weight loss
Teratogenic Effects
ethosuximid
Antiepileptic Drug
Inhibits voltage-activated Ca2+ channels and thus inhibits rhythmic activity
= T type
Treat: ABSENCE SEIZURES
Pharmacokinetics:
- Well absorbed orally
- Not bound to Plasma Proteins
- Long half life (30-60hr)
- 75% metabolized by hepatic enzymes (p450)
- 25% excreted in urine
gabapentin
Antiepileptic drug therapy
Treatment of simple or complex partial seizures
Generalized tonic-clonic seziures
Blocks Ca channels (binding to a2-delta subunit)
Releases glutamate
Enhances GABAergic synaptic transmission
Not metabolized/ does not include hepatic enzymes
Not bound to plasma proteins
Short half-life (5-8hrs)
Elimination by kidneys
Negligible drug interactions
lamotrigine
Antiepileptic Drug
- Goal to prevent seizures while minimizing side-effects, by using simplest drug regimen
Alters ionic conductance to suppress firing of action potential:
- Inhibits voltage-activated Na channels to prolong the refractory period and reduce sustained firing
Treatment:
- Simple
- Complex Partial
- Tonic-clonic
Inhibits release of glutamate (suppresses excitatory tone)
Blocks voltage-activated Na channels (prevents repetitive firing)
Metabolized by liver
Drug interaction: half-life time of lamotrigine decreased by enzyme inducing drugs (carbamazepine, phenytoin) and is increased by valproic acid
phenobarbital
Barbiturate but part of antiepileptic drug therapy also
Works on abnormal ligand-gated channels
Steps in Seizures:
- Focal Epileptogenesis
- Synchronization
Enhances inhibitory GABAerigc neurotransmission
Works on:
- Simple Partial
- Recurrent tonic-clonic seizures
- Febrile seizures in children
Faciliates GABA receptors to increase inhibitory tone
Pharmacokinetics
- Well absorbed orally
- Freely penetrates brain
- 75% inactivated by hepatic microsomal system
- Metabolite of primidone also
Teratogenic
phenytoin
Antiepileptic Drug
- Goal to prevent seizures while minimizing side-effects, by using simplest drug regimen
Mechanism:
- Blocks abnormal voltage-gated channels
- Blocks the Focal Epileptogenesis step in seizure
Alters ionic conductance to suppress firing of action potential:
- Inhibits voltage-activated Na channels to prolong the refractory period and reduce sustained firing
Status epilepticus:
- Use IV administration of this long acting drug to keep effects on
Drug of choice for Initial Therapy of Epilepsy in Adults - Effective for: Partial Simple Partial complex Tonic-clonic
Emergency treatment for Status Epilepticus
NOT USED in ABSENCE SEIZURES
Mechanism:
- Blocks Na channels
- Suppresses repetitive action potential firing
- Blocks voltage activated Ca channels
Pharmacokinetics:
- Oral administratino for chronic
- IV for emergency
- Oral absorption slow but distribution is rapid, brain conc is high
- High plasma protein binding (90%)
- 95% is metabolized by p450 system (CYP2C9) and CYP2C19, so can become SATURATED at high dosage (400-600mg)
- Less than 5% is unchanged and excreted by kidneys
Fosphenytoin is prodrug and is rapidly converted to phenytoin
- USED IM and IV
Drug Interactions: Enhances p450 system, increases metabolism of other drugs, doxycycline, cyclosporine
Drugs that stimulate Phenytoin Metabolism: CARBAMAZEPINE
Drugs that inhibit phenytoin metabolism: CHLORAMPHENICOL, SULFONAMIDE
Side Effect:
- Drowsiness, sedation
- Ataxia
- Nausea and vomiting
- Skin Rash
- Metabolic changes
Additional:
- GINGIVAL HYPERPLASIA
- MEGALOBLASTIC ANEMIA
- TERATOGENIC EFFECT
valproic acid
Antiepileptic Drug
Inhibits voltage activated Na channels and thus prolong the refractory period and reduce sustained firing
Inhibits voltage-gated Ca2+ channels and thus inhibits rhytmic activity
Enhance inhibitory GABAergic neurotransmission
Drug of choice for:
- Myoclonic seizures
- Second line drug for tonic-clonic and absence seizures (due to hepatotoxicity)
Mechanism:
- Blocks Na and Ca channels and faciliates GABA synpatic transmission
- Reduces propagation of abnormal electrical discharge in brain
Pharmacokinetics:
- Orally effective/rapidly absrobed
- High level of Plasma Protein binding (90%)
- Metabolized by p450
- Divalproex is combination of Sodium valproate and valproic acid
- Improves GI tolerance
Side Effects:
- Hepatotoxic
- Thrombocytopenia
- Teratogenic Effects
pregabalin
New class of Antiepileptic Drug
Blocks Ca channel (via a2-delta subunit) and blocks release of glutamate
Used for:
- Simple
- Complex Partial seizures
Side Effects:
- Thrombocytopenia
topiramate
New class of antiepileptic drug
- Block Na channel
- Increases activity of postsynatpic GABA receptors
Used for:
- Simple
- Complex partial seizures
- Generalized tonic-clonic seizures
levetiracetam
Antiepileptic Drug Therapy
- Modifies glutamate and GABA release via binding to synaptic protein SV2A
- Adjunctive treatment of:
- Simple
- Complex partial
- Generalized tonic-clonic
clonazepam
Benzodiazepine that enhances GABAergic transmission for treatment of seizures
Treat:
- Myoclonic
- Absence seizures
diazepam
Antiepileptic Drug/Benzodiazepine
Rapid acting antiepileptic that might useful for direct treatment of status epilepticus
Drug of choice for:
Acute emergency treatment of Status Epilepticus
lorazepam
Antiepileptic Drug/Benzodiazepine
Rapid acting antiepileptic that might useful for direct treatment of status epilepticus