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Questions and Answers
Which mechanism of action primarily involves the enhancement of GABA action in antiepileptic drugs?
What is one of the primary clinical uses of carbamazepine?
What is a common side effect associated with the use of phenobarbital?
Which of the following drugs is a strong inducer of hepatic enzymes?
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What is the plasma half-life of carbamazepine approximately?
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Which of the following adverse drug reactions (ADRs) are associated with Carbamazepine?
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What is a potential consequence of using Phenytoin without convulsions?
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Which of the following drugs is specifically indicated for treating absence seizures?
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What is a notable pharmacokinetic property of Phenytoin?
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What type of enzyme activity does Oxcarbazepine have compared to Carbamazepine?
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Which of the following correctly describes the mechanism of action of the drugs mentioned?
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What is the plasma half-life of Valproate, which is commonly used in various types of seizures?
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What is a key side effect of Gabapentin that differentiates it from other antiepileptic drugs?
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Which drug acts as a positive allosteric modulator of GABA-A receptors?
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Which of the following is true concerning dosing frequency for Gabapentin?
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Study Notes
Antiepileptic Drugs
- Antiepileptic drugs inhibit abnormal neuronal discharge but not the underlying cause.
- They work by:
- Enhancing GABA action
- Inhibiting sodium channel function
- Inhibiting calcium channel function
Phenobarbital
- It’s used for the same indications as phenytoin.
- It’s not often used because it causes sedation.
- It's widely used in veterinary practice.
Carbamazepine
- It’s one of the most widely used antiepileptic drugs.
- It's chemically related to tricyclic antidepressants.
- It’s used in certain partial seizures (psychomotor epilepsy).
- It’s used to treat neuropathic pain, manic-depressive illness.
- It's oral administered.
- The plasma half-life is 30 h.
- It's a strong inducer of hepatic enzymes.
- A slow-release preparation is used for patients who experience transient side effects.
- Common side effects are:
- Dizziness, drowsiness, sedation, confusion, loss of coordination
- Nausea, vomiting, dry mouth, constipation
- Leukopenia, thrombocytopenia
- Rash, photosensitivity
- Hormonal effects leading to menstrual irregularities or other endocrine disorders
- Elevated liver enzymes, Hepatitis (rare)
- Allergic reactions
Phenytoin
- Structurally related to the barbiturates.
- It's widely used.
- It's effective against various shapes of partial and generalized seizures.
- It’s not used in the absence of convulsions because it can worsen the situation.
Phenytoin Pharmacokinetics
- It’s well absorbed when given orally.
- It’s highly protein-bound (80–90%).
- Other drugs, such as salicylates, phenylbutazone, and valproate, inhibit this binding competitively (this can enhance or reduce the effect of phenytoin in an unpredictable way).
- It increases the rate of metabolism of other drugs (e.g. oral anticoagulants - warfarin).
- The metabolism of phenytoin itself can be enhanced or inhibited competitively by various other drugs that share the same hepatic enzymes.
Ethosuximide
- It’s effective against absence seizures.
- It inhibits T-type calcium channels.
- It’s well absorbed and metabolized.
- The half-life is 60 h.
- Common side effects are:
- Nausea, anorexia, lethargy, dizziness
- Hypersensitivity reactions (rare)
Valproate
- It’s used in certain types of infantile epilepsy.
- It has low toxicity and lack of sedative action.
- It’s used in adolescents who exhibit both tonic-clonic or myoclonic seizures, as well as absence seizures.
- It’s well absorbed orally and excreted.
- The plasma half-life is approximately 15 h.
- Common side effects are:
- Nausea, vomiting, drowsiness, dizziness, ataxia
- Weight gain
- Liver dysfunction
- Thrombocytopenia
- Hair loss
Gabapentin and Pregabalin
- Gabapentin is used against partial seizures and has less severe side effects.
- The absorption shows high variability.
- It’s relatively safe.
- The half-life is 6 h (resulting in dosing two to three times daily).
- It doesn’t interact with other drugs.
- It’s also used as an analgesic to treat neuropathic pain.
- Pregabalin is an analogue of gabapentin.
- Pregabalin is more potent but otherwise very similar to gabapentin.
- It’s more potent and with caution in patients whose renal function is impaired.
Ganaxolone and Tonabersat
- Ganaxolone is a positive allosteric modulator of GABA-A receptors containing δ subunits.
- Tonabersat is a neuronal gap junction inhibitor.
Benzodiazepines
- They’re used to treat acute seizures, especially in children (diazepam is often administered rectally).
- They’re also used in status epilepticus.
- They act very rapidly (lorazepam, diazepam, or clonazepam are administered intravenously).
Other Uses of Antiepileptic Drugs
- Bipolar disorder (valproate, carbamazepine, oxcarbazepine, lamotrigine, topiramate).
- Migraine prophylaxis (valproate, gabapentin, topiramate).
- Anxiety disorders (gabapentin).
- Neuropathic pain (gabapentin, pregabalin, carbamazepine, lamotrigine).
Antiepileptic Drugs and Women
- They may increase oral contraceptive metabolism, thus reducing their effectiveness.
- They’re thought to produce teratogenic effects by inducing hepatic CYP3A4 enzymes.
- They may result in vitamin K deficiency in the newborn.
Clinical Uses of Antiepileptic Drugs
- Generalized tonic-clonic seizures:
- Carbamazepine (preferred because of a favorable effectiveness/risk ratio), phenytoin, valproate.
- Newer agents include vigabatrin, lamotrigine, topiramate, levetiracetam.
- Use of a single drug is preferred, when possible, to avoid pharmacokinetic interactions.
- Partial (focal) seizures:
- Carbamazepine, valproate.
- Alternatives include clonazepam, phenytoin, gabapentin, pregabalin, lamotrigine, topiramate, levetiracetam, zonisamide.
- Absence seizures:
- Ethosuximide, valproate, lamotrigine.
- Valproate is useful when absence seizures coexist with tonic-clonic seizures, because most other drugs used for tonic-clonic seizures can worsen absence seizures.
- Neuropathic pain:
- Carbamazepine, gabapentin.
- To stabilize mood in mono- or bipolar affective disorder (as an alternative to lithium):
- Carbamazepine, valproate
When to start AED Therapy
- AED therapy should only be started once the diagnosis of epilepsy is confirmed, unless exceptional circumstances.
- The initiation of AED is usually recommended after the second epileptic seizure.
- Consider AED therapy after a first unprovoked seizure if:
- The electroencephalogram shows definite epileptic activity.
- The patient has a neurologic deficit.
- Brain imaging demonstrates structural abnormality.
- Some patients may choose not to take AED therapy after full discussion of risks and benefits.
Choosing AED Therapy
- Individualize AED treatment strategy based on:
- Epilepsy syndrome.
- Seizure type.
- Other medications and comorbidities.
- Patient's lifestyle.
- Preferences of the patient, their family, and/or caregivers as appropriate.
- Choose the AED on the basis of the presenting epilepsy syndrome.
- Treat patients with monotherapy wherever possible.
- If the initial treatment is unsuccessful, switch to monotherapy with a different drug.
- Caution is needed during the changeover period.
Specific Drug Recommendations
-
Carbamazepine:
- Use with caution due to the possibility of causing syndrome of inappropriate antidiuretic hormone secretion (SIADH) or hyponatremia.
- Monitor sodium levels in older adults due to the increased risk of SIADH.
- Offer controlled-release carbamazepine preparations to reduce adverse effects.
-
Valproate:
- It’s the first-line treatment for:
- Newly diagnosed generalized tonic-clonic seizures.
- Newly diagnosed myoclonic seizures.
- Tonic or atonic seizures.
- Newly diagnosed idiopathic generalized epilepsy.
- It’s the first-line treatment for:
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Description
This quiz covers key information about antiepileptic drugs, including their mechanisms of action and specific medications like phenobarbital and carbamazepine. Test your knowledge on their uses, side effects, and clinical applications in both human and veterinary medicine. Ideal for students and professionals in pharmacology and neurology.
