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Questions and Answers
What is the primary mechanism of action of Phenytoin?
What is the primary mechanism of action of Phenytoin?
Which of the following side effects is associated with Carbamazepine?
Which of the following side effects is associated with Carbamazepine?
What therapeutic range is considered optimal for Carbamazepine?
What therapeutic range is considered optimal for Carbamazepine?
Which condition is not an indication for Valproic Acid?
Which condition is not an indication for Valproic Acid?
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Which medication is specifically noted for causing severe skin reactions in individuals with the HLA-B1502 allele?
Which medication is specifically noted for causing severe skin reactions in individuals with the HLA-B1502 allele?
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What is a significant concern when using Valproic Acid?
What is a significant concern when using Valproic Acid?
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What type of seizures is Oxcarbazepine primarily indicated for?
What type of seizures is Oxcarbazepine primarily indicated for?
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Which side effect is common to both Phenytoin and Carbamazepine?
Which side effect is common to both Phenytoin and Carbamazepine?
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Which drug significantly lowers the effectiveness of oral contraceptives?
Which drug significantly lowers the effectiveness of oral contraceptives?
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Which medication primarily blocks T-type Ca++ channels?
Which medication primarily blocks T-type Ca++ channels?
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Which medication acts as an antagonist to the glycine receptor site on the NMDA receptor?
Which medication acts as an antagonist to the glycine receptor site on the NMDA receptor?
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What is a common side effect associated with the use of Topiramate?
What is a common side effect associated with the use of Topiramate?
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What action does Tiagabine perform on GABA activity?
What action does Tiagabine perform on GABA activity?
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Which drug is indicated for adjunct therapy in adults with partial-onset seizures?
Which drug is indicated for adjunct therapy in adults with partial-onset seizures?
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Which side effect is specifically associated with Felbamate?
Which side effect is specifically associated with Felbamate?
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Which of the following is a risk factor associated with Topiramate use during pregnancy?
Which of the following is a risk factor associated with Topiramate use during pregnancy?
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What is the main mechanism of action of Levetiracetam?
What is the main mechanism of action of Levetiracetam?
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Which medication is a known irreversible inhibitor of GABA-T?
Which medication is a known irreversible inhibitor of GABA-T?
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Which medication is known to enhance GABA-mediated inhibition?
Which medication is known to enhance GABA-mediated inhibition?
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What is a notable side effect of Lamotrigine?
What is a notable side effect of Lamotrigine?
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What is the reference range for Primidone levels?
What is the reference range for Primidone levels?
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Which medication should be avoided in absence seizures due to the potential to worsen them?
Which medication should be avoided in absence seizures due to the potential to worsen them?
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What is the primary action of Pregabalin in the treatment of seizures?
What is the primary action of Pregabalin in the treatment of seizures?
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Which of the following is a common side effect associated with Gabapentin?
Which of the following is a common side effect associated with Gabapentin?
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Why should Primidone levels not be monitored independently?
Why should Primidone levels not be monitored independently?
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What is the potential risk of using Phenobarbital during pregnancy?
What is the potential risk of using Phenobarbital during pregnancy?
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Study Notes
Anti-Epileptic Medications
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Phenytoin (Dilantin)
- Mechanism of Action: Blocks sodium channels.
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Indications: Primary generalized and partial seizures.
- First-line treatment for tonic-clonic or partial complex seizures.
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Side Effects:
- Dose-dependent side effects: Nystagmus, Ataxia, Increased seizure frequency, Lethargy, Altered Level of Consciousness, Coma.
- Other common side effects: Gingival hyperplasia, Hirsutism, Coarsening face features, Hyperglycemia, Hematologic effects, Osteoporosis, Rash (including DRESS), Megaloblastic anemia, Teratogenic, Arthralgia, Lymphadenopathy, Agitation, Headache, Hypotension, Tachycardia, Arrhythmia, GI upset.
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Considerations:
- Therapeutic Drug Level: 10-20 mg/L.
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Dose Adjustments based on Therapeutic Levels:
- Levels less than 12 mg/L: Increase dose by 30 mg/day or less.
- 0.74 mg/kg increase will increase level by 1 ug/ml.
- Monitor for albumin and uremia, as these can increase free fraction and cause lab level misinterpretation.
- Hepatitis: May occur due to hypersensitivity reaction.
- Drug Interactions: Allopurinol, Diazepam, Alcohol, Antacids, Calcium, Barbiturates, Carbamazepine, Corticosteroids, Digoxin, Doxycycline, Haloperidol, Oral contraceptives, Levodopa, Furosemide.
- Can worsen absence seizures.
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Carbamazepine (Tegretol)
- Mechanism of Action: Blocks sodium channels, partial agonist of adenosine A2A/A2B receptors.
- Indications: Partial and secondary generalized tonic-clonic seizures, Trigeminal neuralgia, Mood stabilizer for bipolar disorder.
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Side Effects:
- HLA-B1502 allele genetic morphism: Severe rash, Stevens-Johnson Syndrome (SJS), Toxic epidermal necrolysis (TEN) (common in Asian descent individuals).
- Other side effects: Leukopenia, Aplastic anemia, Hyponatremia (stimulates release of ADH), Drowsiness, Fatigue, Nystagmus.
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Considerations:
- Therapeutic Range: 4-12 mg/L.
- Can worsen absence or myoclonic seizures.
- Hepatic elimination: Auto-induction reaches maximum in 2-4 weeks.
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Drug Interactions:
- Decreases effects of warfarin.
- Oral contraceptive failure.
- Erythromycin inhibits metabolism.
- Phenytoin can decrease plasma levels of carbamazepine .
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Oxcarbazepine (Trileptal, Oxtellar)
- Mechanism of Action: Inhibits voltage-sensitive sodium channels and modulates activity of voltage-activated calcium channels.
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Indications: Initial adjunct therapy for partial seizures.
- Off-label use for bipolar disorder.
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Side Effects:
- Fewer side effects than carbamazepine but some cross-reactivity may occur.
- Other side effects: Headache, Dizziness, Nystagmus, Blurry vision, Nausea/Vomiting, Rash, Hyponatremia.
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Considerations:
- Significantly lowers oral contraceptives and increases levels of phenytoin and phenobarbital.
- Pregnancy Category C, Lactation risk.
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Eslicarbazepine (Aptiom)
- Mechanism of Action: Inhibition of voltage-gated sodium channels.
- Indications: Partial-onset seizures.
- Side Effects: Dizziness, Drowsiness, Sedation, Hyponatremia, Diplopia.
- Considerations: Pregnancy Category C, Lactation risk.
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Valproic Acid (Depakene, Depakote)
- Mechanism of Action: Partially blocks sodium currents, may increase GABA levels and its effects by inhibiting its degradation. Also may influence glutamic acid decarboxylase.
- Indications: Complex partial seizures, Status epilepticus, Absence seizures, Bipolar disorder, Migraine prophylaxis.
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Side Effects:
- GI: Nausea, Vomiting, Diarrhea.
- Other side effects: Weight gain, Hepatotoxicity, Pancreatitis, Tremors, Thrombocytopenia, Teratogenicity (due to folate depletion), Hyperammonemia (can lead to encephalopathy).
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Considerations:
- Drug Interactions: Lamotrigine, Phenytoin, Phenobarbital, Carbamazepine, Ethosuximide, AZT.
- Pregnancy Risk D: Neural tube defects, Lactation risk.
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Ethosuximide (Zarontin)
- Mechanism of Action: Primarily blocks thalamic (T-type) calcium channels. Inhibits NADPH-linked aldehyde reductase necessary for formation of gamma-hydroxybutyrate.
- Indications: Absence (petit mal) seizures only.
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Side Effects:
- GI: Nausea, Vomiting, Diarrhea.
- Other side effects: Fatigue, Headache, Psychotic behavior, Rash (SJS), Leukopenia, Lupus-like syndrome.
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Considerations:
- Reference Range: 60-100 mcg/ml (may go up to 125 mcg/ml).
- Dosage: Weight-based dosing in children.
- Monitor complete blood count periodically.
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Phenobarbital (Luminal)
- Mechanism of Action: Barbiturate. Enhances GABA-mediated inhibition via increasing chloride channel opening. Decreases glutamate-mediated excitation on the AMPA receptor. At higher concentrations, blocks calcium currents.
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Indications: Alternative for partial and generalized tonic-clonic seizures.
- Typically used as a second-line agent, but may be preferred in pregnant women.
- Avoid in absence seizures as it can worsen them.
_ Side Effects: Sedation, Development of tolerance.
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Considerations:
- Reference Range: 15-40 mg/L.
- Toxic Levels: Greater than 50 mg/L.
- Pregnancy Category B/D: Depending on the manufacturer.
- Safe in pediatrics.
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Primidone (Mysoline)
- Mechanism of Action: Barbiturate. Unknown mechanism. Its actions are thought to be due to the parent compound and its two active metabolites, phenobarbital and phenylethylmalonamide (PEMA), whose actions may be synergistic.
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Indications: Alternative for partial and generalized tonic-clonic seizures.
- Typically used as a second-line agent, but may be preferred in pregnant women.
- Avoid in absence seizures as it can worsen them.
- Side Effects: CNS depression, Sedation, Confusion, Suicidal ideation, Megaloblastic anemia.
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Considerations:
- Monitor phenobarbital levels instead of primidone levels.
- Reference range for Primidone: 8-12 ug/ml.
- Phenobarbital Levels: 15-30 ug/ml.
- Renal dose adjustment required.
- Avoid in pregnancy: Lowers folate levels and crosses the placenta.
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Lamotrigine
- Mechanism of Action: Blocks voltage-sensitive sodium channels and inhibits glutamate and aspartate release.
- Indications: Partial seizures, Primary generalized tonic-clonic seizures, Seizures associated with Lennox-Gastaut syndrome.
- Side Effects: Nausea, Diplopia, Ataxia, Rash (SJS, especially in children).
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Considerations:
- Safe in children over 2 years old.
- Drug Interactions: Valproate and carbamazepine.
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Gabapentin (Neurontin)
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Mechanism of Action: Binds to an amino acid carrier protein and elevates GABA levels.
- Also binds to subunits on voltage-gated calcium channels.
- Indications: Partial seizures, Postherpetic neuralgia, Peripheral neuropathy, Restless legs syndrome, Post-operative pain, Hot flashes.
- Side Effects: Sedation, Fatigue, Dizziness, Ataxia.
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Considerations:
- Renal dose adjustments required.
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Mechanism of Action: Binds to an amino acid carrier protein and elevates GABA levels.
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Pregabalin (Lyrica)
- Mechanism of Action: GABA analog that strongly binds to the alpha(2)-delta site (a subunit of voltage-gated calcium channels) in CNS tissues. This binding may modulate the release of pro-nociceptive neurotransmitters.
- Indications: Partial-onset seizures (adjunct), Pain associated with peripheral neuropathy, postherpetic neuralgia, Fibromyalgia.
- Side Effects: Edema, Sedation, Dizziness, Blurred vision, Weight gain.
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Considerations:
- Renal dose adjustments required.
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Felbamate (Felbatol)
- Mechanism of Action: Antagonist to the glycine receptor site on the NMDA receptor. Also affects glutamate and sodium channels.
- Indications: Lennox-Gastaut syndrome (not first-line).
- Side Effects: Aplastic anemia, Nausea/Vomiting.
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Tiagabine (Gabitril)
- Mechanism of Action: Thought to enhance GABA activity by inhibiting neuronal uptake.
- Indications: Partial seizures.
- Side Effects: Dizziness, Drowsiness, Difficulty focusing, Weakness.
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Topiramate
- Mechanism of Action: Inhibits sodium channels, enhances GABA, and antagonizes glutamate receptors.
- Indications: Epilepsy, Migraine prophylaxis, Essential tremor, Cluster headache prophylaxis.
- Side Effects: Weight loss, Ataxia, Impaired concentration, Acute angle-closure glaucoma, Metabolic acidosis (due to reduction in bicarbonate), Nephrolithiasis, Hyperammonemia.
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Considerations:
- Pregnancy Category D: Risk of cleft lip.
- Drug Interactions: Phenytoin, Ethinylestradiol, Carbamazepine, Carbonic anhydrase inhibitors.
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Lacosamide
- Mechanism of Action: Dual mode of action: controls neuronal hyperexcitability via selective sodium channel slow inactivation, and binding to collapsin response mediator protein-2 (CRMP-2), which is part of the signal transduction cascade of neurotrophic factors.
- Indications: Adjunctive therapy for partial-onset seizures in epilepsy in adults over 17 years old.
- Side Effects: PR interval prolongation, AV blocks, Dysrhythmias, Suicidal ideation, Dizziness, Ataxia, DRESS (drug reaction of eosinophilia and systemic symptoms).
- Considerations: - Maximum dose of 300 mg daily if renal or hepatic failure exists. - Pregnancy Category C.
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Levetiracetam (Keppra)
- Mechanism of Action: Inhibits voltage-dependent N-type calcium channels. Facilitates GABA-ergic inhibitory transmission. Reduces the delayed rectifier potassium current. Binds to synaptic vesicle protein 2A ligand, which affects neurotransmitter release.
- Indications: Partial seizures, Tonic-clonic seizures, Myoclonic seizures, Status epilepticus.
- Side Effects: Behavioral problems, Weakness, Nausea/Vomiting, Headache.
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Considerations:
- No reference range; no drug levels required.
- No significant drug interactions.
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Brivaracetam
- Mechanism of Action: Analogue to keppra. Binds to synaptic vesicle protein 2A ligand, which affects neurotransmitter release.
- Indications: Partial seizures.
- Side Effects: Drowsiness, Dizziness, Fatigue, Nausea/Vomiting.
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Considerations:
- For patients over 16 years old.
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Vigabatrin (Sabril)
- Mechanism of Action: Irreversible inhibitor of GABA-T, which is responsible for the metabolism of GABA.
- Indications: Adjunct in refractory partial seizures; monotherapy for infantile spasms.
- Side Effects: Retinal toxicity, Intramyelinic edema in children.
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Description
Test your knowledge on anti-epileptic medications, specifically Phenytoin (Dilantin). This quiz covers the mechanism of action, indications for use, side effects, and therapeutic considerations. Perfect for anyone studying neurology or pharmacology!
