NAPLEX Question of the Week: Analyzing Antiepileptic Drugs

This week's question assesses your skills with antiepileptic drugs.
NAPLEX Question of the Week: Analyzing Antiepileptic Drugs
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JP is a 25-year-old male with a history of seizures. His physician would like your help in determining the appropriate regimen for JP to prevent further episodes. In choosing an appropriate drug you consider things like mechanism of action, side effects, drug interactions, allergies, and cost.  Which of the following proposed drug-mechanism of action pairs are correctly matched? Select all that apply.

A. Vimpat – slows inactivation of voltage gated sodium channels

B. Phenytoin – blockage of voltage gated sodium channels

C. Depakote – slows inactivation of voltage gated sodium channels and increases GABA concentrations 

D. Keppra – GABA receptor agonist

E. Zarontin – GABA receptor agonist

Answers with rationale: 

Seizures are bursts of abnormal and uncontrolled electrical activity in the brain. They can manifest in different ways and can include episodes of unconsciousness and jerking movements. To prevent seizures from recurring, maintenance medications are often taken by patients long-term to keep their episodes to a minimum. When choosing a medication for a patient, mechanism of action is important to consider. For example, if a patient has tried and failed a sodium channel blocker, it might be time to try a calcium channel blocker or something that increases the levels of GABA (the major inhibitory neurotransmitter). Many antiepileptic drugs' mechanism(s) of action has not been fully elucidated. However a primary proposed mechanism is postulated based on current evidence.

Brand/Generics covered: Vimpat/Lacosamide; Dilantin/Phenytoin; Depakote/Valproic acid; Keppra/Levetiracetam; Zarontin/Ethosuximide

Choice A is correct. Vimpat or lacosamide is a sodium channel blocker. Sodium channel blockers work because they reduce the rate of depolarization and firing of the action potentials created by sodium, decreasing the release of uncontrolled “bursts” of activity in the brain.

Choice B is also correct as phenytoin or Dilantin is also a sodium channel blocker. Sodium channel blockers work because they reduce the rate of depolarization and firing of the action potentials created by sodium, decreasing the release of uncontrolled “bursts” of activity in the brain.

Choice C is correct. Depakote or valproic acid increases the levels of GABA in the brain and also works through sodium channels. This is effective because GABA is the major inhibitory neurotransmitter in the brain, helping to decrease the uncontrolled activity seen in seizures.

Choice D is incorrect. Keppra or levetiracetam does not act on glutamate receptors. Instead, it binds to SV2A and prevents the release of glutamate (the major excitatory neurotransmitter) from vesicles.

Choice E is also incorrect as Zarontin or ethosuximide is a T-type calcium channel blocker. Calcium channels are also involved in the firing of electrical bursts in the brain like sodium channels. By blocking these, it decreases the uncontrolled firing and reduces the occurrence of seizures.

Therefore the correct answers are A, B, and C. 

NAPLEX Competencies Covered:

Area 2: Identify Drug Characteristics 

2.1 Pharmacology, mechanism of action, or therapeutic class

2.2 Commercial availability; prescription or non-prescription status; brand, generic, or biosimilar names; physical descriptions; or how supplied 

Our latest NAPLEX Review Guide on Access Pharmacy has a chapter for antiepileptic drugs:

NAPLEX Review Guide (4th edition): https://accesspharmacy.mhmedical.com/content.aspx?bookid=3025&sectionid=254103386.

Have a great weekend!

Dr. B

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