Tell your veterinarian what medications your pet is currently using and any new products, including herbal remedies you may start to give. Drug/drug interactions could cause a decrease in effectiveness or an increase in side effects of either Atopica or the other medication being given. Examples of medications that may cause drug/drug interactions are; SMZ-TMP (Bactrim, Septra), gentamicin, etodolac (EtoGesic), piroxicam (Feldene), ketoconazole (Nizoral), cimetidine (Tagamet), ranitidine (Zantac), itraconoazole (Sporanox), methylprednisolone (Medrol), erythromycin, Allopurinol (Zyloprim), metoclopramide (Reglan), prednisOLOne, digoxin (Lanoxin), any type of vaccination.