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Drugs for Epilepsy
| Question | Answer |
|---|---|
| Phenytoin: mechanism of action | Selective inhibition of sodium channels, delaying recovery of inactive state |
| Phenytoin: therapeutic range | Narrow therapeutic range (10-20 mcg/dL); above 20 mcg/dL = toxicity |
| Phenytoin: uses | Partial seizures and tonic clonic seizures. Drug of choice for adults and older children |
| Phenytoin: CNS effects (therapeutic doses) | CNS effects are mild |
| Phenytoin: CNS effects (toxic doses) | Nystagmus, sedation, ataxia, diplopia, cognitive impairment |
| Phenytoin: adverse effects (unique) | Gingival hyperplasia, purple glove syndrome, hirsutism |
| Phenytoin: adverse effects (pregnancy) | Teratogenic. Can cause cleft palate, heart malformations, fetal hydantoin syndrome. Decreases synthesis of vitamin K-dependent clotting factors |
| Phenytoin: adverse effects (reactions) | Morbilliform rash, rarely SJS or TEN. FDA recommends testing for HLA-B*1502 in Asian patients |
| Phenytoin: adverse effects (CV) | Cardiac dysrhythmia and hypotension. Contraindicated in patients with heart block |
| Phenytoin: drug interactions | Decreases effects of oral contraceptives, warfarin, glucocorticosteroids |
| Phenytoin: drug interactions that increase phenytoin levels | Diazepam, isoniazid, cimetidine, and alcohol. Also valproic acid |
| Phenytoin: drug interactions that decreases phenytoin levels | Carbamazepine, phenobarbital, and alcohol. Breakthrough seizures can occur |
| Phenytoin: drug interactions that increases CNS effects | Alcohol, barbiturates, CNS depressants |
| Phenytoin: IV administration uses and adverse effects | Used for generalized SE and should be infused slowly because rapid administration can cause cardiovascular collapse |
| Carbamazepine: mechanism of action | Delays recovery of sodium channels from inactivated state |
| Carbamazepine: uses | Partial and tonic-clonic seizures. First choice for partial seizures. Preferred to use in younger children. Also used for bipolar disorder and neuralgia associated with trigeminal and glossopharyngeal nerves |
| Carbamazepine: adverse effects (CNS) | Minimal effect on cognitive function. Preferred over phenytoin or phenobarbital. Administer larger doses at bedtime to reduce adverse CNS effects |
| Carbamazepine: adverse effects (unique) | Induces bone marrow suppression (leukopenia, anemia, thrombocytopenia). Contraindicated in patients with pre-existing hematologic abnormalities |
| Carbamazepine: adverse effects (pregnancy) | Teratogenic, increased risk of spina bifida |
| Carbamazepine: adverse effects (reactions) | Morbilliform rash, photosensitivity, SJS, TEN. FDA recommends testing for HLA-B*1502 in Asian patients |
| Carbamazepine: adverse effects (renal) | Hypoosmolarity due to inhibition of renal excretion of water. Use with caution in patients with heart failure |
| Carbamazepine: drug interactions | Decreases effects of oral contraceptives and warfarin |
| Carbamazepine: drug interactions that decreases carbamazepine levels | Phenytoin and phenobarbital |
| Carbamazepine: drug interactions and increases carbamazepine levels | Grapefruit juice |
| Valproic acid: mechanism of action | Blocks sodium channels, suppresses calcium influx through T-type calcium channels, augment inhibitory influence of GABA |
| Valproic acid: uses | First line drug for all major seizure types. Also used for bipolar disorder and prophylaxis of migraines |
| Valproic acid: adverse effects (most common) | Nausea, vomiting, ingestion |
| Valproic acid: adverse effects (rare) | Hepatotoxicity, pancreatitis |
| Valproic acid: adverse effects (pregnancy) | Teratogenic, NTDs |
| Valproic acid: adverse effects (other) | Rash, weight gain, hair loss, tremor, blood dyscrasia |
| Valproic acid: drug interactions | Topiramate increases risk of hyperammonemia (S/S vomiting, lethargy, altered LOC, altered cognitive function). Valproic acid also increases phenobarbital and phenytoin levels. |
| Valproic acid: drug interactions that decreases valproic acid levels | Carbapenem antibiotics (meropenem and impenem/cilastatin) |
| Ethosuximide: mechanism of action | Inhibits T-type calcium channels |
| Ethosuximide: pharmacokinetics | Does not induce drug-metabolizing enzymes |
| Ethosuximide: uses | Absence seizures |
| Ethosuximide: adverse effects | No significant adverse effects. Drowsiness, dizziness, lethargy with initial treatment (but diminishes with continued use). Nausea and vomiting may occur |
| Ethosuximide: adverse effects (rare) | Systemic lupus erythematosus, leukopenia, aplastic anemia, SJS |
| Ethosuximide: drug interactions | No significant drug interactions |
| Phenobarbital: mechanism of action | Binds to GABA receptors, potentiating effects of GABA |
| Phenobarbital: uses | Partial seizures and tonic-clonic seizures. Also used for daytime sedation and to promote night time sleep |
| Phenobarbital: adverse effects (CNS) | Drowsiness, sedation with initial treatment, depression in adults. Agitation and confusion in elderly. Paradoxical hyperexcitability in children |
| Phenobarbital: adverse effects (toxic) | Nystagmus, ataxia, CNS depression, respiratory depression, death |
| Phenobarbital: adverse effects (pregnancy) | Teratogenic. Decreases vitamin K-dependent clotting factors |
| Phenobarbital: adverse effects (unique) | Increases risk of acute intermittent porphyria. Contraindicated in patients with history of intermittent porphyria. Can also cause physical dependence and disrupts vitamin D metabolism |
| Phenobarbital: drug interactions | Decreases effects of oral contraceptives and warfarin |
| Phenobarbital: drug interactions that increase phenobarbital levels | Valproic acid |
| Phenobarbital: drug interactions that increase CNS effects | Benzodiazepines, opioids, alcohol, other CNS depressants |
| Gabapentin: mechanism of action | Unknown. Probably promotes GABA release |
| Gabapentin: uses | Adjunct to partial seizure therapy. Recommended for mono therapy. Postherpetic neuralgia |
| Gabapentin: uses (off label) | Neuropathic pain, prophylaxis of migraines, fibromyalgia, postmenopausal hot flushes |
| Gabapentin: adverse effects | Somnolence, dizziness, ataxia, fatigue, nystagmus, peripheral edema (but diminishes over continued use) |
| Gabapentin: adverse effects (pregnancy) | Safety not established |
| Gabapentin: drug interaction | No significant drug interactions |
| Levetiracetam: mechanism of action | Unknown but it does not bind to GABA receptors |
| Levetiracetam: uses | 1) Myoclonic seizures in adults and adolescents over 12 2) Partial seizures in adults and children over 4 3) Tonic-clonic seizures in adults and children over 6 |
| Levetiracetam: uses (off label) | Migraine, bipolar disorder, new onset of pediatric epilepsy |
| Levetiracetam: adverse effects | Drowsiness, asthenia |
| Levetiracetam: adverse effects (CNS) | Agitation, anxiety, depression, psychosis, hallucinations, depersonalizations |
| Levetiracetam: adverse effects (pregnancy) | Safety not established |
| Levetiracetam: drug interactions | No interactions |
Created by:
suezy
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