None — Fluoroquinolone for Cats
Cats are one of the most popular pets in American households. In the U.S., there are more than 86 million pet cats. The American Pet Products Association estimates about 38.9 million homes have at least one cat.
When cats get sick, they may be given an antibiotic to fight off a bacterial infection. One kind of antibiotic is fluoroquinolone (Baytril®). Katrina Mealey, D.V.M., Ph.D., Veterinary Pharmacologist with the College of Veterinary Medicine, Washington State University in Pullman, WA, says fluoroquinolone is commonly prescribed to treat urinary tract infections, respiratory infections and some types of skin infections. At recommended doses, fluoroquinolone is generally a safe medication for most cats. However, at higher doses, the drug is associated with blindness.
Mealey says researchers have discovered that cats have a defect in a protein, called ABCG2. Normally, this protein keeps drugs and other toxic substances out of the retina. When ABCG2 is defective, fluoroquinolone accumulates in the retina. Light shining onto the retina initiates a chemical reaction, causing the fluoroquinolone to turn into a toxic substance that damages the retinal cells.
Researchers report signs of this photosensitive reaction can develop anywhere from 2 to 3 days after starting the drug. In some cases, the reaction may not occur for weeks. A pet owner may notice the cat is more frequently bumping into objects, shows signs of confusion or is no longer willing to jump onto a familiar surface (like the bed or a counter). Visual examination of eye shows a wide dilation (enlargement) of the pupils and slow or nonexistent pupil dilation in response to a bright light. Mealey adds there is no treatment to reverse the damage, so the blindness is permanent.
A Possible Human Link?
Mealey says the fluoroquinolone retinal toxicity appears to be unique to cats. The drug is sometimes used to treat humans with certain diseases. However, exposure to sunlight in people causes a photosensitivity reaction in the skin. So people who take fluoroquinolones are generally advised to stay out of the sun while taking the drug.
In her investigation on the cause of fluoroquinolone toxicity, Mealey discovered a different kind of connection for humans. A group of anti-cancer drugs, called tyrosine kinase inhibitors, appear to inhibit the action of the ABCG2 protein. Thus, there may be the potential that cancer patients who are also given fluoroquinolone could develop the same kind of retinal phototoxicity as cats.
Mealey says further research needs to be done to look at the possible link between tyrosine kinase inhibitors, fluoroquinolone and human blindness. In the meantime, she continues her research on the problem in cats. Mealey reminds owners that fluoroquinolone is safe for most cats when given at the proper doses. The only exception is for cats with kidney disease, who are less able to eliminate the drug from their systems, so it may accumulate to dangerous levels. To reduce the risk for developing blindness, Mealey recommends owners keep cats who are taking fluoroquinolone indoors with the shades down.
Research compiled and edited by Barbara J. Fister
If you have any questions or concerns about the use of fluoroquinolone or other medications for your cat, speak with your veterinarian.