Dosage and Adverse Effects of Commonly Used Antiepileptic Drugs
| Generic Name | Trade Name | Principal Uses | Typical Dose; Dose Interval | Half-Life | Therapeutic Range | Adverse Effects | Drug Interactionsa | |
|---|---|---|---|---|---|---|---|---|
| Neurologic | Systemic | |||||||
| Carbamazepine | Tegretolc | Tonic-clonic Focal-onset | 600-1800 mg/d (15-35 mg/kg, child); bid (capsules or tablets), tid-qid (oral suspension) | 10-17 h (variable due to autoinduction: complete 3-5 wk after initiation) | 4-12 µg/mL | Ataxia Dizziness Diplopia Vertigo | Aplastic anemia Leukopenia Gastrointestinal irritation Hepatotoxicity Hyponatremia | Level decreased by enzyme-inducing drugsb Level increased by erythromycin, propoxyphene, isoniazid, cimetidine, fluoxetine |
| Clobazam | Onfi | Lennox-Gastaut syndrome | 10-40 mg/d (5-20 mg/d for patients <30 kg body weight); bid | 36-42 h (71-82 h for less active metabolite) | Not established | Fatigue Sedation Ataxia Aggression Insomnia | Constipation Anorexia Skin rash | Level increased by CYP2C19 inhibitors |
| Clonazepam | Klonopin | Absence Atypical absence Myoclonic | 1-12 mg/d; qd-tid | 24-48 h | 10-70 ng/mL | Ataxia Sedation Lethargy | Anorexia | Level decreased by enzyme-inducing drugsb |
| Ethosuximide | Zarontin | Absence | 750-1250 mg/d (20-40 mg/kg); qd-bid | 60 h, adult 30 h, child | 40-100 µg/mL | Ataxia Lethargy Headache | Gastrointestinal irritation Skin rash Bone marrow suppression | Level decreased by enzyme-inducing drugsb Level increased by valproic acid |
| Ezogabine | Potiga | Focal-onset | 800-1200 mg/d; tid | 7-11 h | Not established | Dizziness Fatigue Sedation Confusion Vertigo Tremor | Retinal abnormalities Skin discoloration Cardiac conduction (QT interval prolongation) Urinary retention | Level decreased by enzyme-inducing drugsb |
| Felbamate | Felbatol | Focal-onset Lennox-Gastaut syndrome Tonic-clonic | 2400-3600 mg/d, tid-qid | 16-22 h | 30-60 µg/mL | Insomnia Dizziness Sedation Headache | Aplastic anemia Hepatic failure Weight loss Gastrointestinal irritation | Increases phenytoin, valproic acid, active carbamazepine metabolite |
| Gabapentin | Neurontin | Focal-onset | 900-2400 mg/d; tid-qid | 5-9 h | 2-20 µg/mL | Sedation Dizziness Ataxia Fatigue | Gastrointestinal irritation Weight gain Edema | No known significant interactions |
| Lacosamide | Vimpat | Focal-onset | 200-400 mg/d; bid | 13 h | Not established | Dizziness Ataxia Diplopia Vertigo | Gastrointestinal irritation Cardiac conduction (PR interval prolongation) | Level decreased by enzyme-inducing drugsb |
| Lamotrigine | Lamictalc | Focal-onset Tonic-clonic Atypical absence Myoclonic Lennox-Gastaut syndrome | 150-500 mg/d; bid (immediate release), daily (extended release) (lower daily dose for regimens with valproic acid; higher daily dose for regimens with an enzyme inducer) | 25 h 14 h (with enzyme-inducers), 59 h (with valproic acid) | 2.5-20 µg/mL | Dizziness Diplopia Sedation Ataxia Headache | Skin rash Stevens-Johnson syndrome | Level decreased by enzyme-inducing drugsb and oral contraceptives Level increased by valproic acid |
| Levetiracetam | Kepprac | Focal-onset | 1000-3000 mg/d; bid (immediate release), daily (extended release) | 6-8 h | 5-45 µg/mL | Sedation Fatigue Incoordination Mood changes | Anemia Leukopenia | No known significant interactions |
| Oxcarbazepinec | Trileptal | Focal-onset Tonic-clonic | 900-2400 mg/d (30-45 mg/kg, child); bid | 10-17 h (for active metabolite) | 10-35 µg/mL | Fatigue Ataxia Dizziness Diplopia Vertigo Headache | See carbamazepine | Level decreased by enzyme-inducing drugsb May increase phenytoin |
| Phenobarbital | Luminal | Tonic-clonic Focal-onset | 60-180 mg/d; qd-tid | 90 h | 10-40 µg/mL | Sedation Ataxia Confusion Dizziness Decreased libido Depression | Skin rash | Level increased by valproic acid, phenytoin |
| Phenytoin (diphenylhydantoin) | Dilantin | Tonic-clonic Focal-onset | 300-400 mg/d (3-6 mg/kg, adult; 4-8 mg/kg, child); qd-tid | 24 h (wide variation, dose-dependent) | 10-20 µg/mL | Dizziness Diplopia Ataxia Incoordination Confusion | Gingival hyperplasia Lymphadenopathy Hirsutism Osteomalacia Facial coarsening Skin rash | Level increased by isoniazid, sulfonamides, fluoxetine Level decreased by enzyme-inducing drugsb Altered folate metabolism |
| Primidone | Mysoline | Tonic-clonic Focal-onset | 750-1000 mg/d; bid-tid | Primidone, 8-15 h Phenobarbital, 90 h | Primidone, 4-12 µg/mL Phenobarbital, 10-40 µg/mL | Same as phenobarbital | Level increased by valproic acid Level decreased by phenytoin (increased conversion to phenobarbital) | |
| Rufinamide | Banzel | Lennox-Gastaut syndrome | 3200 mg/d (45 mg/kg, child); bid | 6-10 h | Not established | Sedation Fatigue Dizziness Ataxia Headache Diplopia | Gastrointestinal irritation Leukopenia Cardiac conduction (QT interval shortening) | Level decreased by enzyme-inducing drugsb Level increased by valproic acid May increase phenytoin |
| Tiagabine | Gabitril | Focal-onset | 32-56 mg/d; bid-qid (as adjunct to enzyme-inducing antiepileptic drug regimen) | 2-5 h (with enzyme inducer), 7-9 h (without enzyme inducer) | Not established | Confusion Sedation Depression Dizziness Speech or language problems Paresthesias Psychosis | Gastrointestinal irritation | Level decreased by enzyme-inducing drugsb |
| Topiramate | Topamax | Focal-onset Tonic-clonic Lennox-Gastaut syndrome | 200-400 mg/d; bid (immediate release), daily (extended release) | 20 h (immediate release), 30 h (extended release) | 2-20 µg/mL | Psychomotor slowing Sedation Speech or language problems Fatigue Paresthesias | Renal stones (avoid use with other carbonic anhydrase inhibitors) Glaucoma Weight loss Hypohidrosis | Level decreased by enzyme-inducing drugsb |
| Valproic acid (valproate sodium, divalproex sodium) | Depakotec | Tonic-clonic Absence Atypical absence Myoclonic Focal-onset Atonic | 750-2000 mg/d (20-60 mg/kg); bid-qid (immediate and delayed release), daily (extended release) | 15 h | 50-125 µg/mL | Ataxia Sedation Tremor | Hepatotoxicity Thrombocytopenia Gastrointestinal irritation Weight gain Transient alopecia Hyperammonemia | Level decreased by enzyme-inducing drugsb |
| Zonisamide | Zonegran | Focal-onset Tonic-clonic | 200-400 mg/d; qd-bid | 50-68 h | 10-40 µg/mL | Sedation Dizziness Confusion Headache Psychosis | Anorexia Renal stones Hypohidrosis | Level decreased by enzyme-inducing drugsb |
aExamples only; please refer to other sources for comprehensive listings of all potential drug-drug interactions.
bPhenytoin, carbamazepine, phenobarbital.
cExtended-release product available.