Antiepileptic Drugs

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Barbiturates

Back 1

- facilitate GABAergic transmission (may act at Cl ionophore of receptor)
- cause widespread CNS depression
- ultra-short-acting (20 min): thiopental; used as IV anesthetic
- intermediate-acting (3-8 hrs): pentobarbital and secobarbital
- long-acting (1-2 days): phenobarbital
- adverse effects: daytime hangover, cross-tolerance, respiratory depression, paradoxical excitement (esp in kids and elderly), tachyphylaxis

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Phenobarbital

Back 2

- long-acting barbiturate; half-life ~90 hrs
- enhances GABAergic transmission
- use to treat seizures (often concurrently with phenytoin); given IV for status epilepticus
- agent of choice for seizures in children <5
- induces CYP
- 25% eliminated by renal excretion
- side effects: sedation, fatigue

Front 3

Secobarbital

Back 3

- intermediate-acting barbiturate (3-8 hrs)
- hypnotic

Front 4

Pentobarbital

Back 4

- intermediate-acting barbiturate (3-8 hrs)
- hypnotic

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Thiopental

Back 5

- ultra-short-acting barbiturate (20 min)
- action terminated by redistribution and metabolism

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Phenytoin

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- antiepileptic
- prolongs Na inactivation --> reduction in high frequency firing
- primary agent to treat tonic-clonic, cortical focal and psychomotor seizures, esp for pts >5; given IV for status epilepticus
- dose dependent elimination (zero order at high concs)
- induces CYP
- side effects: sedation (less than phenobarbital), ataxia, nystagmus, nausea, gingival hyperplasia, hirsutism

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Carbamazepine

Back 7

- blocks Na channels; related to TCAs
- use to treat partial and grand mal seizures (but not absence), trigeminal neuralgia, bipolar disorder
- given orally; CYP metabolism & induction
- advantages over phenytoin: does not cause gingival hyperplasia or hirsutism
- side effects: sedation, vertigo, potentially serious liver and bone marrow probs

Front 8

Ethosuximide

Back 8

- blocks Ca T channels --> reduces slow frequency, pacemaker-driven repetitive firing
- use to treat absence seizures
- side effects: nausea, lethargy, ataxia; serious side effects unlikely

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Valproate

Back 9

- antiepileptic
- valproic acid used to treat absence seizures; also tonic-clonic and coritcal focal
- short half life, mostly hepatic metabolism
- side effects less likely than with other drugs
- given orally as divalproex, valproic acid, valproate sodium
- administer with other drugs: inhibits metabolism of phenobarbital, phenytoin, divalproex, lamotrigine, and lorazepam

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Pregabalin

Back 10

- inhibits excitatory NT release in CNS
- used to treat partial seizures, neuropathic pain
- >90% renal elimination; no CYP involvement

Front 11

Vigabatrin

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- antiepileptic; inhibits the catabolism of GABA (irreversibly inhibits GABA transaminase)
- minimal/no DDI

Front 12

Gabapentin

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- antiepileptic; GABA analog
- used to treat partial seizures, postherpetic neuralgia
- excreted unchanged in urine
- minimal/no DDI, mild adverse effects

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Tiagabine

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- inhibits neuronal and glial uptake of GABA
- used to treat partial seizures, esp complex
- CYP3A4 metabolism

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Topiramate

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- inhibits carbonic anhydrase, which may affect GABAergic transmission
- used to treat partial and tonic-clonic seizures; also migraine
- renal elimination
- inhibits CYP2C19

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Lamotrigine

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- blocks Na channels and high voltage-dependent Ca channels
- used to treat partial and tonic-clonic seizures; also bipolar disorder

Front 16

Clonazepam

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- benzodiazepine used to suppress absence seizures
- substantial tolerance to anti-seizure activity can develop; can cause restlessness and hyperactivity in kids --> not first choice drug

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Partial seizures

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- treat with phenytoin or carbamazepine

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Absence seizures

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- treat with ethosuximide or valproic acid

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Tonic-clonic (grand mal) seizures

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- treat with phenytoin, carbamazepine, or valproic acid

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Status epilepticus

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- treat with diazepam, lorazepam, phenytoin, or phenobarbital

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Anti-epileptics

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- start and stop tx gradually
- monitor plasma drug conc when starting tx
- use multi-drug therapy only when monotherapy is clearly insufficient
- also used to treat neuropathic pain, migraine, movement disorders, trigeminal neuralgia, and psych disorders (bipolar disorder and schizophrenia)