San Ren Tang is a very commonly used Chinese Herbal formula that has a long list of indications. In your cat's case it has been prescribed because it is a drying anti-inflammatory formula for the gastrointestinal system, which will help for Colitis, Constipation, Fecal Incontinence, Vomiting and Inappetance. San Ren Tang also clears heat and can also help with asthma, and since it is an anti-inflammatory may help with the swollen larynx. However, if your cat's asthma is severe he may require additional herbs for the asthma such as Bu Fei Tang, thou San Ren Tang may be enough, given enough time. Herbal formulas tend to take a bit more time to reach full effectiveness than drugs.
Thank you for the information, it was quite helpful. He has a follow-up appt in the New Year. We'll see how he makes out. Thanks again!