Chronic Respiratory Problems

If an animal isn't consistently breathing clearly-- when one listens with a stethoscope, not just the naked ear pressed to a chest-- then long term treatment with one or both drugs may be required to keep the Myco at bay. These are pretty reliable drugs, although sometimes you and the vet can go through several drugs until you find something effective. Long term drugs can be a moderately expensive proposition, but often you can keep an animal stable and comfortable for an extended period of time-- anywhere from a few weeks to many months (equivalent to years of a dog's or human's life).

When treating a crisis situation, dosing is usually twice a day but don't be afraid to add in an extra full or half dose at a mid-way point (6-8 hours) the first day or two. You want to really nuke the Myco. It's a very deadly organism which can exist sub-clinically in a rat, doing much damage while you blithely think all is well because the animal no longer sounds rattly or snuffly to the naked ear. Myco not only damages lungs, it causes hearts to overwork to compensate for ineffective lungs. Speaking from experience, you don't want to be dealing with Myco damaged lungs and congestive heart failure or a weakening heart in the same animal. It's not fun-- for you or the animal in question.

Give your rat a decongestant and/or expectorant.
The simplest, safest expectorant is old-fashioned Antimonium Tartaricum, which is usually available in homeopathic pharmacies. Give one 30X tablet 3 times a day. The lactose-based soft tablets dissolve in less than 5 seconds in the mouth and can be dissolved instantly in a drop of water (and then lapped up or squirted into the mouth of a really ill animal). The rock-hard little pellets can be chewed by a cooperative rodent or dissolved in the space of a few minutes in water.
Infant Dimetapp syrup is an excellent pharmaceutical choice. It's alcohol-free, grape-flavored, and the packaging tells you clearly how much to give, depending on the weight (in pounds and kilograms) of the "infant." The only side effect MAY be a bit of sleepiness; on the plus side, this can help to calm an animal having a panic attack or really gasping for breath. Standard dose would be every 6-8 hours.
Guaifenesin syrup is a good expectorant. One of the varieties of Robitussen is just guaifenesin, but you may be able to find a less-well-known label for about half the price. Guaifenesin is a standard remedy for dogs and cats that are congested, so your vet should be familiar with the veterinary form of this. Dosing can be a bit tricky, because there can be side effects of agitation. Debbie Ducummon's rule of thumb, when in a real emergency situation, is to start with 1/10 the dose you would give a child.
Sudafed decongestant syrup can also be used on rats with good results.
Steam your rat. Take him into the bathroom when it's really steamy for at least 10 minutes at a time. Monitor whether he's truly suffocating with the steam (too steamy) or just a bit choked by it, but benefiting afterward by the thinning of any mucus in his lungs. After the steaming, see if you can get him to really run around and take deep breaths. This will encourage him to sneeze or cough out any mucus that's been thinned by the steam.
Put a steam vaporizer by your rat's cage and let him decide how close he wants to get. Many congested animals are smart enough to keep their heads as close to the steam as possible, for great lengths of time. The steam thins the phlegm in the breathing passages (nose and lungs) so that it can be sneezed out more easily. Some vets advocate adding Vicks Vaporub or eucalyptus essential oil to the medicine well of a vaporizer, but these are *so* strong that some rats are overwhelmed by the smell in their sensitive little noses that it can be more annoying than helpful.
Cold vaporizers do not sterilize the water vapor and can contribute to spreading germs, especially what's popularly called "humidifier fever."
Support your rat with a vitamin boost, in the form of NutriCal or Felovite or similar vitamin paste. Or put small animal (hamster) vitamin drops in his drinking water (but make sure you clean the water bottle regularly with hot water and soap, and preferably a bottle brush, because scum will form along the sides of the bottle).
If your rat's lung function is poor or the vet hears any permanent or semi-permanent wheeze (from damage to tissues) try a bronchodilator such as Ventolin. This comes in veterinary form as a liquid and you would probably give him one drop once or twice a day. This *can* have a side effect of some degree of agitation (just ask any human who takes Ventolin in puffer form for asthma or stubborn bronchitis), but if it helps the breathing you can adjust the dosage, for example, by putting the drop of Ventolin in a tiny gob of pudding, mixing well with a toothpick, and letting him eat only half the gob.
If you do end up with fluid buildup in the chest, you can flush the fluid out with an oral or indictable diuretic and a low-salt diet. The two diuretics recommended for rats are furosemide (Lasix) and hydrochlorothiazide.
If your rat is ever quarantined due to ill health, a cuddle buddy is a good idea. Fill a shampoo bottle or something similar with warm water, wrap it in an old sock, and leave it in your rat's sleeping box.
Remember, watch for side effects with *any* medicine. Agitation, with increased heart rate or additional stress of any kind with the heart, or stupefaction, with clumsiness or depressed heart action, would be the most likely effects with most drugs.