antiepileptic

Question 1

Phenytoin

Answer 1

inhibit excitation
block voltage-gated sodium channels → ⇓ initiation of action potential

Nonseizure indications: trigeminal neuralgia

slow absorption(oral); antacids decrease absorption; highly bound to plasma protein; zero-order elimination

Small therapeutic index and pregnancy category D

Adverse effects: gingival hyperplasia, nystagmus, ataxia, vertigo, tremor, lethargy, slurred speech, blurred vision, lymphadenopathy, hyperglycemia, coarsening of the face, and hirsutism

Drugs interaction (affecting liver enzymes): fluconazole inhibits phenytoin metabolism

Question 2

Carbamazepine

Answer 2

inhibit excitation
block voltage-gated sodium channels → ⇓ initiation of action potential

Also:
Nonseizure indications: trigeminal neuralgia and bipolar disorder

Pregnancy category D: evidence of human fetal risk

Adverse effects: dizziness, drowsiness, problems with walking and coordination, nausea and vomiting, liver problem, rash, aplastic anemia, agranulocytosis

Drugs interaction: the risk or severity of adverse effects of selegiline can be increased when combined with carbamazepine

Question 3

Valproic acid

Answer 3

inhibit excitation
block voltage-gated sodium channels → ⇓ initiation of action potential

Nonseizure indications: bipolar disorder

Pregnancy category X: the risk to pregnant women clearly outweighs any possible benefit, may cause spina bifida (teratogenic)

Adverse effects: CNS depression, hair loss, GI upset, hyperglycemia, hyperuricemia, weight gain, thrombocytopenia, and hepatic toxicity (especially in patients < 2 years old and patients with multiple medications)

Drugs interaction: metabolic inhibitor to other anticonvulsants (phenobarbital and phenytoin)

Question 4

Gabapentin

Answer 4

inhibit excitation

block voltage-gated calcium channels → ⇓ neurotransmitter release

Question 5

Levetiracetam

Answer 5

inhibit excitation

interact with synaptic vesicle protein → ⇓ neurotransmitter release

Question 6

Topiramate

Answer 6

Do both:
block voltage-gated sodium channels;
block glutamate receptor (AMPA/kainate); allosteric activation of GABA receptor

Question 7

Phenobarbital

Answer 7

Enhance Inhibition
allosteric activation of GABA receptor → ⇑ inhibitory effect of GABA

Nonseizure indications: pain and anxiety, high potential for abuse

Pregnancy category D: pregnant women who take barbiturates during the third trimester can give birth to addicted infants who undergo an extended withdrawal syndrome

Small therapeutic index: coma and death

Adverse effects: CNS depression, respiratory depression, and hepatic toxicity

Drugs interaction: risk of OD is greatly increased when phenobarbital is combined with alcohol
therapy for partial and tonic-clonic seizures.
long duration of action

Question 8

Benzodiazepines

Answer 8

Enhance Inhibition

allosteric activation of GABA receptor → ⇑ inhibitory effect of GABA

Question 9

Tiagabine

Answer 9

Enhance Inhibition
binds GAT1 (GABA transporter 1) to inhibit GABA reuptake→ ⇑ [GABA]

Question 10

Vigabatrin

Answer 10

Enhance Inhibition

inhibitor of GABA-T, the enzyme responsible for GABA degradation → ⇑ [GABA]