Hi Joe,
What did you treat the burmese with? I ask because many antibiotics are prescribed very liberally for reptiles that are intended specifically for other groups of animals entirely. Such as Baytril. It is an antibiotic intended for use on canines only and even says so right on the bottles. Baytril is a very strong antibiotic that can actually do more harm than good in reptiles. Reptile organs are a lot more sensitive to harsh antibiotics than those of mammals. Many well-meaning vets just don't know this and prescribe it anyway. I think very little, if any, research has been done to determine which antibiotics are safest for reptiles. Most if not all antibiotics commonly prescribed for reptile ailments were developed specifically for dogs, birds or farm animals. What with the reptile industry/hobby being so large and growing so fast I think it is high time that reptile-specific antibiotics are researched and developed and made available to her hobbyists.
That rant over with it's time to get back to y'alls burmese. Okay, I don't know where your vet is getting his information that "burmese have a lot of mucous" but he's not correct. Coughing up mucous, even clear mucous, is an indication that something is wrong. It is my guess, based on the fact that he had an RI 7 months ago that he is either relapsing or has excess mucous that he needs to expel. One thing about snakes is that they take a long time to overcome an RI. Usually many months. Sometimes over a year. Burmese are notorious for relapsing shortly after undergoing antibiotic treatment and getting even sicker than before due to damaged kidneys and liver due to the harsh antibiotics developed for mammals.
My advice to you would be to find another vet that has more reptile-specific knowledge and have a culture done on the mucous to determine if there is bacterial infection in addition to the mucous. If there is infection I would suggest a long-term treatment with a milder antibiotic rather than a short-term treatment with a strong antibiotic. If there is no bacterial infection then keep him between 88 and 92 and maintain his humidity levels between 75 and 85%. Also, keep him hydrated. Even if you have to inject his food with pedialyte or electrolytes from your vet. This is readily absorbed and will keep him very hydrated. This coupled with very humid air will ensure that his mucous buildup will remain very wet and pliant and thus it won't be apt to clog his trachea. This will give him time to expel it safely and comfortably and get it out of his system.
I hope this helps. Best of luck to you.
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David Beauchemin
High End Herps.Inc
http://HighEndHerps.com