Hello I am Dr. Joey. Thanks for trusting me to help you and your pet today. I am a licensed veterinarian with over 15 years of experience. I look forward to working with you.
I am so sorry Minx is experiencing this. Certainly the nasal drops can sometimes be useful, but cats do not like them at all and I find their effect, if any, is fleeting.
With congestion such as this if she has any color to her nasal discharge (yellow, green, white) then there is a secondary bacterial infection which would benefit an antibiotic (such as doxycycline or clavamox or azithromycin). Sadly, we cannot prescribe anything for you from online. This legally requires an examination and relationship with your veterinarian. However, since you already took her in to be seen you should be able to phone your vet and (s)he will prescribe something. If she has not been seen, then this is probably your next step.
I can also make some at-home hints as well to try.
First, let me mention some possible causes for this. The most common cause of chronic upper respiratory congestion is a viral infection (especially either feline herpes virus or feline calici virus). Alternatively, this may not be due to a virus but due to a fungal infection or nasal foreign object (highly unlikely given how long she has had the problem; this usually resolves itself within 1-3 weeks or gets so severe you have to do something) or polyp or tumor or even dental disease. Rarely we do have cats with chronic rhinitis (inflammation) that can be very difficult to contend with but in her case this is very possible given how long she has had the issue. Most cases we start with treatment for the viral infection (feline herpes) since this is the most common with a combination of an antibiotic and l-lysine +/- nebulization. I do also worry that an antibiotic one-time treatment is not going to clear this problem. It is really worth working with your vet to determine if that might be the case (treat first and see if improves).
What can you do at home that might work better than the nasal drops?
If she was my patient and you were unable to have her seen in the next 24-48 hours, then I might recommend you try:
1) Start her on an l-lysine supplement such as Viralys (Amazon linK: http://www.amazon.com/Vetoquinol-410633-Viralys-Powder-100gm/dp/B000FULBT4/ref=sr_1_1?ie=UTF8&qid=1447901872&sr=8-1&keywords=viralys) which helps provide for her what she needs to clear the virus. No bad side effects. I find the flavored cat products are easier to get into cats than the non-flavored human products, although you can use a people capsule (and mix the powder in 1 capsule with moist food once daily).
2) Nebulization- you can purchase a nebulizer at most pharmacies for people. And then you would nebulize about 6 ml of sterile saline once daily. This really aids in breaking up congestion.
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