indication

For the treatment of epilepsy

pharmacology

Primidone is a barbiturate with anticonvulsant properties. Primidone, either alone or used concomitantly with other anticonvulsants, is indicated in the control of grand mal, psychomotor, and focal epileptic seizures. It may control grand mal seizures refractory to other anticonvulsant therapy. Primidone raises electro- or chemoshock seizure thresholds or alters seizure patterns in experimental animals. Primidone per se has anticonvulsant activity as do its two metabolites, phenobarbital and phenylethylmalonamide (PEMA). In addition to its anticonvulsant activity, Primidone potentiates that of phenobarbital in experimental animals.

mechanism of action

Primidone is a GABA receptor agonist. The mechanism of Primidone's antiepileptic action is not known.

toxicity

Symptoms of an overdose typically include sluggishness, incoordination, difficulty in thinking, slowness of speech, faulty judgment, drowsiness or coma, shallow breathing, staggering, and in severe cases coma and death.

biotransformation

Hepatic

absorption

90 to 100%

half life

3-23 hours

drug interactions

Acenocoumarol: The barbiturate, primidone, decreases the anticoagulant effect of acenocoumarol.

Aminophylline: The barbiturate, primidone, decreases the effect of aminophylline.

Anisindione: The barbiturate, primidone, decreases the anticoagulant effect of anisindione.

Betamethasone: The barbiturate, primidone, may decrease the effect of the corticosteroid, betamethasone.

Chlorotrianisene: The enzyme inducer, primidone, decreases the effect of the hormone agent, chlorotrianisene.

Clomifene: The enzyme inducer, primidone, decreases the effect of the hormone agent, clomifene.

Conjugated Estrogens: The enzyme inducer, primidone, decreases the effect of the hormone agent, conjugated estrogens.

Cortisone acetate: The barbiturate, primidone, may decrease the effect of the corticosteroid, cortisone acetate.

Cyclosporine: The barbiturate, primidone, increases the effect of cyclosporine.

Dexamethasone: The barbiturate, primidone, may decrease the effect of the corticosteroid, dexamethasone.

Dicumarol: The barbiturate, primidone, decreases the anticoagulant effect, dicumarol.

Diethylstilbestrol: The enzyme inducer, primidone, may decrease the effect of the hormone agent, diethylstilbestrol.

Doxycycline: The anticonvulsant, primidone, decreases the effect of doxycycline.

Dyphylline: The barbiturate, primidone, decreases the effect of dyphylline.

Estradiol: The enzyme inducer, primidone, decreases the effect of the hormone agent, estradiol.

Estriol: The enzyme inducer, primidone, decreases the effect of the hormone agent, estriol.

Estrone: The enzyme inducer, primidone, decreases the effect of the hormone agent, estrone.

Estropipate: The enzyme inducer, primidone, decreases the effect of the hormone agent, estropipate.

Ethinyl Estradiol: This product may cause a slight decrease of contraceptive effect

Felbamate: Felbamate may increase the effect and toxicity of primidone.

Felodipine: The barbiturate, primidone, decreases the effect of felodipine.

Fludrocortisone: The barbiturate, primidone, may decrease the effect of the corticosteroid, fludrocortisone.

Folic Acid: Folic acid decreases the effect of anticonvulsant, primidone.

Gefitinib: The CYP3A4 inducer, primidone, may decrease the serum concentration and therapeutic effects of gefitinib.

Griseofulvin: The barbiturate, primidone, decreases the effect of griseofulvin.

Hydrocortisone: The barbiturate, primidone, may decrease the effect of the corticosteroid, hydrocortisone.

Levonorgestrel: Phenobarbital decreases the effect of levonorgestrel

Medroxyprogesterone: The enzyme inducer, primidone, may decrease the effect of the hormone, medroxyprogesterone.

Megestrol: The enzyme inducer, primidone, may decrease the effect of the hormone, megestrol.

Mestranol: This product may cause a slight decrease of contraceptive effect

Methadone: The barbiturate, primidone, decreases the effect of methadone.

Methoxyflurane: The barbiturate, primidone, increases the renal toxicity of methoxyflurane.

Methylprednisolone: The barbiturate, primidone, may decrease the effect of the corticosteroid, methylprednisolone.

Metoprolol: The barbiturate decreases the effect of metabolized beta-blocker

Metronidazole: The barbiturate, primidone, decreases the effect of metronidazole.

Nifedipine: The barbiturate, primidone, decreases the effect of the calcium channel blocker, nifedipine.

Norethindrone: This product may cause a slight decrease of contraceptive effect

Oxtriphylline: The barbiturate, primidone, decreases the effect of oxtriphylline.

Paramethasone: The barbiturate, primidone, may decrease the effect of the corticosteroid, paramethasone.

Prednisolone: The barbiturate, primidone, may decrease the effect of the corticosteroid, prednisolone.

Prednisone: The barbiturate, primidone, may decrease the effect of the corticosteroid, prednisone.

Propranolol: The barbiturate decreases the effect of metabolized beta-blocker

Quinestrol: The enzyme inducer, primidone, decreases the effect of the hormone agent, quinestrol.

Quinidine: The anticonvulsant, primidone, decreases the effect of quinidine.

Telithromycin: Primidone may decrease the plasma concentration of Telithromycin. Consider alternate therapy.

Temsirolimus: Primidone may increase the metabolism of Temsirolimus decreasing its efficacy. Concomitant therapy should be avoided.

Theophylline: The barbiturate, primidone, decreases the effect of theophylline.

Tramadol: Primidone may decrease the effect of Tramadol by increasing Tramadol metabolism and clearance.

Trazodone: The CYP3A4 inducer, Primidone, may decrease Trazodone efficacy by increasing Trazodone metabolism and clearance. Monitor for changes in Trazodone efficacy/toxicity if Primidone is initiated, discontinued or dose changed.

Tretinoin: The strong CYP2C8 inducer, Primidone, may increase the metabolism and clearance of oral Tretinoin. Consider alternate therapy to avoid failure of Tretinoin therapy or monitor for changes in Tretinoin effectiveness and adverse/toxic effects if Primidone is initiated, discontinued or dose changed.

Triamcinolone: The barbiturate, primidone, may decrease the effect of the corticosteroid, triamcinolone.

Triprolidine: The CNS depressants, Triprolidine and Primidone, may increase adverse/toxic effects due to additivity. Monitor for increased CNS depressant effects during concomitant therapy.

Verapamil: The barbiturate, primidone, decreases the effect of the calcium channel blocker, verapamil.

Voriconazole: The barbiturate, primidone, decreases the effect of voriconazole.

Warfarin: The barbiturate, primidone, decreases the anticoagulant effect of warfarin.