Drug interactions
Consult your veterinarian before using any other medications with phenobarbital, even vitamins and supplements. Interactions may occur with acetaminophen, NSAIDs (e.g., aspirin, carprofen, firocoxib, etodolac, deracoxib, and meloxicam), MAO inhibitors (amitraz, selegiline), phenytoin, and rifampin. Antihistamines, chloramphenicol, felbamate, opiates, phenothyazines, urinary acidifiers, and valproic acid may increase the effects of phenobarbital. Phenobarbital may decrease the effect of oral anticoagulants (blood thinners, warfarin), beta blockers (propranolol), chloramphenicol, corticosteroids (e.g., prednisone, dexamethasone), doxycycline, griseofulvin,itraconasole, levothyroxine, metronidazole, praziquantel, theophylline, tricycline antidepressants, urinary alkalinzers, zonisamide.