ANTIEPILEPTIC DRUGS (MOA AND S.E.)
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What is the effect of Phenytoin on the sodium channel?

  • It causes repolarization and opens the channel
  • It blocks the channel and prevents sodium flow (correct)
  • It causes depolarization and closes the channel
  • It activates the channel and allows potassium flow

    • What happens to the sodium channel when Phenytoin is present?

  • The gate remains open, allowing sodium to flow
  • The gate becomes stuck, causing uncontrolled sodium flow
  • The gate closes, preventing sodium from flowing (correct)
  • The gate becomes partially open, allowing some sodium to flow

    • What is the effect of Phenytoin on the resting state of the sodium channel?

  • It causes the channel to fluctuate between open and closed states
  • It causes the channel to open and allow sodium flow
  • It has no effect on the resting state of the channel
  • It causes the channel to close and prevent sodium flow (correct)

    • What is the mechanism of action of Phenytoin?

    <p>It blocks the sodium channel</p> Signup and view all the answers

    What is the result of Phenytoin's action on the sodium channel?

    <p>Decreased sodium flow into the cell</p> Signup and view all the answers

    What happens to the action potential when Phenytoin is present?

    <p>It becomes weaker and less frequent</p> Signup and view all the answers

    What is the effect of Phenytoin on depolarization?

    <p>It decreases depolarization</p> Signup and view all the answers

    What is the net result of Phenytoin's action on the cell?

    <p>Decreased excitability</p> Signup and view all the answers

    What is the effect of barbiturates on the GABAA receptor?

    <p>To prolong the opening of the channel elicited by GABA</p> Signup and view all the answers

    What type of currents are activated at weak depolarization potentials?

    <p>T-type currents</p> Signup and view all the answers

    Which type of blockers do T-type currents resist?

    <p>P/Q-type blockers and L-type blockers</p> Signup and view all the answers

    What is the effect of GABA on muscle and endocrine cells?

    <p>Initiating contraction and secretion</p> Signup and view all the answers

    What is a characteristic of T-type currents?

    <p>Fast inactivation</p> Signup and view all the answers

    What is the relationship between barbiturates and the GABAA receptor?

    <p>Barbiturates are positive allosteric modulators of the GABAA receptor</p> Signup and view all the answers

    What is the mechanism of action of carbamazepine?

    <p>By blocking Na+ and Ca2+ influx into the neuronal axon</p> Signup and view all the answers

    What is the indication of carbamazepine?

    <p>Partial seizures and generalized tonic-clonic seizures</p> Signup and view all the answers

    What is the adverse effect of carbamazepine?

    <p>Bone marrow depression</p> Signup and view all the answers

    What is the characteristic of L-type calcium channels?

    <p>Require strong depolarization and are blocked by organic calcium antagonists</p> Signup and view all the answers

    What is the mechanism of action of phenobarbital?

    <p>By increasing the duration of opening of chloride channels</p> Signup and view all the answers

    What is the mechanism of action of ethosuximide?

    <p>By blocking T-type calcium channels</p> Signup and view all the answers

    What is the refractory state of Na+ channels?

    <p>Inactivated state</p> Signup and view all the answers

    What is the mechanism of action of hydantoin?

    <p>By blocking Na+ channels</p> Signup and view all the answers

    Which antiepileptic drug is most useful in treating partial and generalized tonic-clonic seizures?

    <p>Phenobarbital</p> Signup and view all the answers

    Which of the following mechanisms of action is shared by benzodiazepines and barbiturates?

    <p>GABAA receptor agonist</p> Signup and view all the answers

    What is the primary function of GABA in the brain?

    <p>To slow down brain activity and maintain a sense of calmness</p> Signup and view all the answers

    What is the effect of benzodiazepines on the chloride channel?

    <p>Open the chloride channel in response to GABA activation</p> Signup and view all the answers

    Which type of cell types are involved in the shaping of action potentials and controlling patterns of repetitive firing?

    <p>A wide variety of cell types</p> Signup and view all the answers

    Which of the following antiepileptic drugs has a dual mechanism of action?

    <p>Topiramate</p> Signup and view all the answers

    What is the effect of Phenobarbital on the GABAergic system?

    <p>It enhances the inhibitory effect of GABA</p> Signup and view all the answers

    What is the mechanism of action of tiagabine?

    <p>GABA reuptake inhibitor</p> Signup and view all the answers

    What is the primary use of Phenobarbital?

    <p>As an anticonvulsant</p> Signup and view all the answers

    What is the mechanism of action of Phenobarbital?

    <p>It enhances the inhibitory effect of GABA</p> Signup and view all the answers

    Which of the following antiepileptic drugs is a GABA-T inhibitor?

    <p>Vigabatrin</p> Signup and view all the answers

    What is the effect of GABA on neuronal firing?

    <p>Decrease neuronal firing</p> Signup and view all the answers

    What is the result of GABA's action on the brain?

    <p>A sense of calmness and relaxation</p> Signup and view all the answers

    What type of barbiturate is Phenobarbital?

    <p>Long-acting barbiturate</p> Signup and view all the answers

    Which of the following antiepileptic drugs is effective in treating partial and generalized seizures, and has a dual mechanism of action?

    <p>Topiramate</p> Signup and view all the answers

    What is the mechanism of action of valproic acid?

    <p>Unknown, but has a dual mechanism of action</p> Signup and view all the answers

    What is the effect of Phenobarbital on seizure threshold?

    <p>It elevates the seizure threshold</p> Signup and view all the answers

    Which of the following antiepileptic drugs is a GABAA receptor agonist?

    <p>Barbiturates</p> Signup and view all the answers

    What is the primary advantage of using Phenobarbital as an anticonvulsant?

    <p>It is used as an alternative when single, non-sedating anti-convulsants are unsuccessful</p> Signup and view all the answers

    What is the effect of GABA on neuronal activity?

    <p>It decreases neuronal activity</p> Signup and view all the answers

    Study Notes

    Phenytoin (PTN)

    • Mechanism of action: Blocks Na+ channel, stabilizes membrane by blocking Na+ and Ca2+ influx into neuronal axon, and inhibits release of excitatory amino acids via Ca2+ influx blockade
    • Action on Na+ channel: Resting state, arrival of action potential, activation, and refractory state

    Carbamazepine

    • Mechanism of action: Similar to phenytoin
    • Indications: Partial seizures, generalized tonic-clonic seizures (but worsens absence seizures)
    • Adverse effects: Bone marrow depression (neutropenia, thrombocytopenia, aplastic anemia)

    Ethosuximide

    • Mechanism of action: Ca2+ channel blocker
    • Characteristics of Ca++ channel: L-type currents require strong depolarization, are long-lasting, and are blocked by organic calcium antagonists

    Phenobarbital (Luminal)

    • Mechanism of action: Enhances the inhibitory effect of GABA, elevates seizure threshold, and prevents spread of electrical seizure activity
    • Increases inhibitory neurotransmitters (e.g., GABA) and decreases excitatory transmission
    • Uses: Effective anticonvulsant, primarily used as an alternative when single, non-sedating anti-convulsants are unsuccessful in controlling seizures
    • Most useful in treating partial and generalized tonic-clonic seizures

    GABA (Gamma-AminoButyric Acid)

    • Function: Like the brakes in a car, slows down brain activity, helps us relax and maintain a sense of calmness
    • AEDs that interfere with GABA transmission: GABAA receptor agonists, GABA-T inhibitors, GABA reuptake inhibitors

    GABA-T Inhibitors

    • Examples: Valproic acid, Vigabatrin

    GABA Reuptake Inhibitors

    • Examples: Tiagabine

    Benzodiazepines (BZD)

    • Mechanism of action: Enhance GABA effect, bound to Cl- channels
    • Effects: Sedative, hypnotic, anticonvulsant, muscle-relaxant

    Topiramate

    • Mechanism of action: Dual or multiple mechanisms of action
    • AED with dual or more mechanisms of action: Gabapentin, Lamotrigine, Zonisamide, Valproic acid, Felbamate

    Zonisamide

    • Mechanism of action: Unclear, but may involve blockade of sodium channels and enhancement of GABA-mediated inhibition

    Valproic Acid (Sodium Valproate)

    • Mechanism of action: Unclear, but may involve multiple mechanisms, including GABA-T inhibition, K+ channel opening, and Na+ channel blockade

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    Description

    This quiz covers the mechanism and action of Phenytoin on sodium channels, including its effects in the resting state.

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