Congratulations on adopting an adult cat from a shelter. It is great that you have given Peanut a home and are trying to take care of her medical problems.
Upper respiratory problems can be very frustrating and can take a long time to get under control. Some cats have chronic eye and/or nasal discharge. I have not used the PCR testing because my understanding is that they can be misleading. If the test identifies a bacteria or virus which leads to successful treatment then that is great. However, I have read that they can have false positives and negatives, which means that the results may not be completely reliable. Mycoplasma can be in a normal cat's nose so it may be causing the problem or it may just be there and not be the true cause. It was a good course of action for your veterinarian to place your cat on Doxycycline. Since there are still symptoms, it may be persistent Mycoplasma or there could be contributing bacteria or viruses.
Herpes virus is very common in cats and a cat at a shelter has a very good chance of having been exposed to it. Even though the PCR was negative for Herpes, I don't know that I would rule it out. I have had many patients with chronic eye or nasal discharge or sneezing improve with L-Lysine supplements. L-Lysine is an amino acid that helps reduce the replication of Herpes and helps to reduce the symptoms. It is worth a try for a few weeks. It usually takes 1-2 weeks to see effect and some cats need to be on it for months or years. There are some good veterinary formulations of it that are easy to give to cats so ask your veterinarian if they can dispense some for you.
If the symptoms continue, it is a good idea to have further testing done at the internal medicine doctor as your veterinarian suggested. A rhinoscopy can look into the nasal passages and a CT can examined the entire head.
Make sure you are also providing high quality canned food and a stress-free home. This can help your cat's immune system to fight the disease. Good luck, I hope you find some relief for your kitty.
Judy Karnia, DVM
Scottsdale Cat Clinic
I forgot to add: make sure you are using a dust-free litter and that your cat is not exposed to smoke or other irritating smells in the house. Cats are very sensitive.
thanks for your response to my question; it was very helpful to hear another perspective.
It has been almost 2 weeks since my last message and unfortunately, Peanut's eye condition has not really improved. we experienced a problem with his medication which was compounded into a tuna flavored suspension and shipped to us. During shipment, the medicine somehow settled and the pharmacist believes that for a week or so, Peanut was not receiving the entire dose of doxy so we basically "lost" about 10 days of meds and started a new 2-3 week cycle on 9/18.
Peanut's eye continues to be very watery with the same amt of clear discharge and he's becoming extremely difficult about taking the doxy. Last night and this morning he really fought us, foamed at the mouth, and scratched my husband. (my husband is almost 6 ft tall and strong but this cat is very stubborn. we had 2 very sick cats this year who passed away -one to cancer and one to FIP- so we are pretty experienced in giving cats medicine.)
i'm so frustrated because the medicine doesn't seem to be helping at all, and the cat hates us, hardly eats and just wants to hide under the bed when we're around. i'm beginning to wish we had just taken him to a specialist instead of continuing with a second round of this medicine.
Is it normal to take this long to see improvement in the eye while on doxy? is it bad to give such a long course of doxy? (we started with flavored chew tabs in early August but he caught on and stopped eating them so we use the liquid suspension.)
i realize many cats out there are much much sicker than Peanut, but we want him to be healthy and enjoy his life without all this stress so maybe someday he can learn to trust us. any thoughts on peanut's case would be much appreciated.- Amy
If the main symptom now is the eye discharge, I would see if there is an animal eye specialist near to you to take Peanut. They will know the best course of treatment for the eye.
Have you started any L-Lysine yet?
I would also schedule a recheck with your vet and talk to him about the troubles with the doxycycline. Generally if the cat is tolerating the antibiotics well (no gastrointestinal signs) it is okay to give long term and it some cases that is what is needed.