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Cats + Medications & Supplements

  • Fentanyl is an opioid medication used off-label to treat pain in cats and dogs. It is often given as an injection in hospital, but patches may be prescribed to deliver fentanyl transdermally (through the skin) for pets at home. This handout describes common side effects, risk factors, and drug interactions. If a negative reaction occurs, please call your veterinary office.

  • Ferrous sulfate is given by mouth and is used off label to treat iron-deficiency. Use as directed by your veterinarian. Common side effects include gastrointestinal upset such as discomfort, constipation, nausea, vomiting, and diarrhea. Do not use in pets that are allergic to it. If a negative reaction occurs, please call your veterinary office.

  • Fipronil is used topically to treat flea, tick, and chewing lice infestations. Side effects are uncommon but may include skin irritation at the application site. Do not use this product on pets less than 8 weeks old, geriatric pets, or sick/weak pets.

  • Fish oil is an over-the-counter supplement, given by mouth, that is commonly used to treat a wide variety of inflammatory conditions. Give as directed by your veterinarian. Side effects are not common but may include vomiting, diarrhea, or a fishy odor. Do not use concurrently with anticoagulant medications. If a negative reaction occurs, please call your veterinary office.

  • Flaxseed oil is derived from flax plant seeds and contains high levels of alpha-linolenic acid (ALA), an omega-3 fatty acid, and is used to treat certain inflammatory conditions. Give as directed by your veterinarian. Side effects may include diarrhea, vomiting, delayed wound healing, or an oily coat and skin flakes. Serious side effects include persistent stomach upset, or pancreatitis. Flaxseed oil should not be used in pets that are allergic to it. If a negative reaction occurs, please call your veterinary office.

  • Fleas are the most common nuisance and parasite affecting cats, and an infestation can lead to serious health problems. Flea control requires a three-pronged approach; they need to be eliminated from 1) your cat, 2) any other cats and dogs that you have, 3) your home and yard. There are many flea control products available and your veterinarian can help you determine which are safest and most effective for your pets.

  • Flower essences are an over the counter supplement given by mouth or applied topically to treat stress or anxiety. Give as directed by your veterinarian. There are no known side effects. Do not use in pets that are allergic to it or that are pregnant or nursing. Flower essences should be used cautiously in debilitated pets or pets in organ failure. If a negative reaction occurs, please call your veterinary office.

  • Fluconazole is an antifungal medication used off label in cats, dogs, and small mammals to treat fungal infections, especially those in the brain and spinal cord. It is given by mouth in the form of a tablet or liquid suspension and is also available as an injection for hospital use. It should be used with caution in pets with liver or kidney disease, or pregnant or lactating pets.

  • Fludrocortisone acetate is given by mouth and is used off label to treat hypoadrenocorticism (Addison’s disease) and hyperkalemia. Give as directed by your veterinarian. Side effects are uncommon but may include vomiting. Do not use in pets that are allergic to it or in lactating pets without using a milk replacer. If a negative reaction occurs, please call your veterinary office.

  • Fluocinolone + acetonide DMSO (brand name Synotic®) is applied topically and is labeled to treat ear inflammation in dogs. It is also used off-label to treat ear infections in cats. Give as directed. Side effects are rare but may include temporary hearing loss or skin reactions. Do not use on pets allergic to corticosteroids or DMSO, on pets with a ruptured ear drum or pets that are pregnant.