Reducing Mucus In Cats. Guaifenesin is classified as an expectorant drug, which means that it works by both reducing the amount of phlegm and mucous secreted by the trachea and bronchi in the cat's respiratory passageways, and reducing the viscosity of the remaining secretions. Treatments for mucus in cats if the cat is facing great breathing complications, the vet might place it in the oxygen chamber or put the oxygen mask.
What you can do in the meantime. Use the decongestants with caution. The use of a humidifier, a vaporizer, or the steam from a hot shower may help your cat breathe more easily.