Narrow-Spectrum Anti-seizure Meds

Carbamazepine

Blocks Na channels.

Also used for trigeminal neuralgia.

Boxed Warnings: SJS/TEN (HLA-B*1502 allele testing required), asplastic anemia, agranulocytosis

CI: myelosuppression

Warnings: hyponatremia (SIADH), hypothyroidism, fetal harm

SE: alopecia

Monitoring: CBC w/ differential (including plt), LFTs

Notes:

• Strong inducer + Auto-inducer

• Therapeutic range: 4-12 mcg/mL

Oxcarbaxepine

Warnings: HLA-B*1502 testing required and hyponatremia

Monitor: Na serum (especially during the first 3 months)

Note:

• Not an auto-inducer - It’s a CYP3A4 inducer and CYP2C19 inhibitors.

• Lowers hormonal contraceptives levels.

• XR tablet - Take on empty stomach 1 hr before or 2 hr after a meal.

*Similar to carbamazepine

Lacosamide (C-V)

Warnings: Prolongs PR, increases risk of arrhythmias, DRESS

SE: HA, diplopia, ataxia, tremor, euphoria

Notes:

• Substrate of CYP2C19, 2C9, and 3A4.

• Caution with meds that prolong PR (e.g., beta-blocker, CCB, digoxin)

Phenytoin and Fosphenytoin

Blocks Na channels.

Therapeutic range of Phenytoin: 10-20 mcg/mL (total level) and 1-2 mcg/mL (free level).

IV to PO ratio 1:1

Boxed Warning: IV Phenytoin rate should not exceed 50 mg/min and IV Fosphenytoin, 150 PE/min. If given faster, hypotension and cardiac arrhythmias can occur.

Warnings: extravasation (purple glove syndrome), HLAB*1502 (+) test (avoid), fetal harm

SE:

• Dose-related toxicity: nystagmus, ataxia, diplopia

• Chronic: gingival hyperplasia, hepatotoxicity

Monitor: Serum phenytoin concentration and LFTs

• For IV, monitor cardiac and respiratory function.

Notes:

• Strong inducers.

• Use alternative, non-hormonal contraceptive with chronic phenytoin tx.

• High protein binding.

Phenobarbital (C-IV)

Enhances GABA effect.

CI: severe hepatic impairment, airway obstruction

Warnings: substance use disorder, fetal harm, respiratory depression

SE: physiologic dependence, tolerance, residual sedation

Notes:

• Primidone is prodrug of phenobarbital.

• Strong inducers.

• Lowers hormonal contraceptive levels.