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?

It blocks the sodium channel Signup and view all the answers

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

Decreased sodium flow into the cell Signup and view all the answers

What happens to the action potential when Phenytoin is present?

It becomes weaker and less frequent Signup and view all the answers

What is the effect of Phenytoin on depolarization?

It decreases depolarization Signup and view all the answers

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

Decreased excitability Signup and view all the answers

What is the effect of barbiturates on the GABAA receptor?

To prolong the opening of the channel elicited by GABA Signup and view all the answers

What type of currents are activated at weak depolarization potentials?

T-type currents Signup and view all the answers

Which type of blockers do T-type currents resist?

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

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

Initiating contraction and secretion Signup and view all the answers

What is a characteristic of T-type currents?

Fast inactivation Signup and view all the answers

What is the relationship between barbiturates and the GABAA receptor?

Barbiturates are positive allosteric modulators of the GABAA receptor Signup and view all the answers

What is the mechanism of action of carbamazepine?

By blocking Na+ and Ca2+ influx into the neuronal axon Signup and view all the answers

What is the indication of carbamazepine?

Partial seizures and generalized tonic-clonic seizures Signup and view all the answers

What is the adverse effect of carbamazepine?

Bone marrow depression Signup and view all the answers

What is the characteristic of L-type calcium channels?

Require strong depolarization and are blocked by organic calcium antagonists Signup and view all the answers

What is the mechanism of action of phenobarbital?

By increasing the duration of opening of chloride channels Signup and view all the answers

What is the mechanism of action of ethosuximide?

By blocking T-type calcium channels Signup and view all the answers

What is the refractory state of Na+ channels?

Inactivated state Signup and view all the answers

What is the mechanism of action of hydantoin?

By blocking Na+ channels Signup and view all the answers

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

Phenobarbital Signup and view all the answers

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

GABAA receptor agonist Signup and view all the answers

What is the primary function of GABA in the brain?

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

What is the effect of benzodiazepines on the chloride channel?

Open the chloride channel in response to GABA activation 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?

A wide variety of cell types Signup and view all the answers

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

Topiramate Signup and view all the answers

What is the effect of Phenobarbital on the GABAergic system?

It enhances the inhibitory effect of GABA Signup and view all the answers

What is the mechanism of action of tiagabine?

GABA reuptake inhibitor Signup and view all the answers

What is the primary use of Phenobarbital?

As an anticonvulsant Signup and view all the answers

What is the mechanism of action of Phenobarbital?

It enhances the inhibitory effect of GABA Signup and view all the answers

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

Vigabatrin Signup and view all the answers

What is the effect of GABA on neuronal firing?

Decrease neuronal firing Signup and view all the answers

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

A sense of calmness and relaxation Signup and view all the answers

What type of barbiturate is Phenobarbital?

Long-acting barbiturate 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?

Topiramate Signup and view all the answers

What is the mechanism of action of valproic acid?

Unknown, but has a dual mechanism of action Signup and view all the answers

What is the effect of Phenobarbital on seizure threshold?

It elevates the seizure threshold Signup and view all the answers

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

Barbiturates Signup and view all the answers

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

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

What is the effect of GABA on neuronal activity?

It decreases neuronal activity 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.