| Anticonvulsant Drugs: Carbamazepine, Ethosuximide, Lamotrigine, Phenobarbital, Phenytoin, Primidone, Valproic AcidInterfering Factors - Blood drawn in serum separator tubes (gel tubes).
- Contraindicated in patients with liver disease, and caution advised in patients with renal impairment.
- Drugs that may increase carbamazepine levels or increase risk of toxicity include acetazolamide, azithromycin, bepridil, cimetidine, danazol, diltiazem, erythromycin, felodipine, fluoxetine, flurithromycin, fluvoxamine, gemfibrozil, isoniazid, itraconazole, josamycin, ketoconazole, loratadine, macrolides, niacinamide, nicardipine, nifedipine, nimodipine, nisoldipine, propoxyphene, ritonavir, terfenadine, troleandomycin, valproic acid, verapamil, and viloxazine.
- Drugs that may decrease carbamazepine levels include phenobarbital, phenytoin, and primidone.
- Carbamazepine may affect other body chemistries as seen by a decrease in calcium, sodium, T3, T4 levels, and WBC count and increase in ALT, alkaline phosphatase, ammonia, AST, and bilirubin levels.
- Drugs that may increase ethosuximide levels include isoniazid, ritonavir, and valproic acid.
- Drugs that may decrease ethosuximide levels include phenobarbital, phenytoin, and primidone.
- Drugs that may increase lamotrigine levels include valproic acid.
- Drugs that may decrease lamotrigine levels include acetaminophen, carbamazepine, hydantoins (e.g., phenytoin), oral contraceptives, orlistat, oxcarbazepine, phenobarbital, primidone, protease inhibitors (e.g., ritonavir), rifamycins (e.g., rifampin), and succinimides (e.g., ethosuximide).
- Drugs that may increase phenobarbital levels or increase risk of toxicity include barbital drugs, furosemide, primidone, salicylates, and valproic acid.
- Phenobarbital may affect the metabolism of other drugs, increasing their effectiveness, such as β-blockers, chloramphenicol, corticosteroids, doxycycline, griseofulvin, haloperidol, methylphenidate, phenothiazines, phenylbutazone, propoxyphene, quinidine, theophylline, tricyclic antidepressants, and valproic acid.
- Phenobarbital may affect the metabolism of other drugs, decreasing their effectiveness, such as chloramphenicol, cyclosporine, ethosuximide, oral anticoagulants, oral contraceptives, phenytoin, theophylline, vitamin D, and vitamin K.
- Phenobarbital is an active metabolite of primidone, and both drug levels should be monitored while the patient is receiving primidone to avoid either toxic or subtherapeutic levels of both medications.
- Phenobarbital may affect other body chemistries as seen by a decrease in bilirubin and calcium levels and increase in alkaline phosphatase, ammonia, and gamma glutamyl transferase levels.
- Drugs that may increase phenytoin levels or increase the risk of phenytoin toxicity include amiodarone, azapropazone, carbamazepine, chloramphenicol, cimetidine, disulfiram, ethanol, fluconazole,halothane, ibuprofen, imipramine, levodopa, metronidazole, miconazole, nifedipine, phenylbutazone, sulfonamides, trazodone, tricyclic antidepressants, and trimethoprim. Small changes in formulation (i.e., changes in brand) also may increase phenytoin levels or increase the risk of phenytoin toxicity.
- Drugs that may decrease phenytoin levels include bleomycin, carbamazepine, cisplatin, disulfiram, folic acid, intravenous fluids containing glucose, nitrofurantoin, oxacillin, rifampin, salicylates, and vinblastine.
- Primidone decreases the effectiveness of carbamazepine, ethosuximide, felbamate, lamotrigine, oral anticoagulants, oxcarbazepine, topiramate, and valproate.
- Primidone may affect other body chemistries as seen by a decrease in calcium levels and increase in alkaline phosphatase levels.
- Drugs that may increase valproic acid levels or increase risk of toxicity include dicumarol, phenylbutazone, and high doses of salicylate.
- Drugs that may decrease valproic acid levels include carbamazepine, phenobarbital, phenytoin, and primidone.
Anticonvulsant Drugs: Carbamazepine, Ethosuximide, Lamotrigine, Phenobarbital, Phenytoin, Primidone, Valproic Acid has been found in Davis's Lab & Diagnostic Tests
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