not familier with the antibiotics used for Respiratory infection. For the other poster who's dragon died 3 hours after leaving the vet, it was most likely too far gone to be saved.
High humidity can cuase repiratory infections in bearded dragons. It would be a good ideal to use a dehumidifier in the room the dragon's cage is in, or if you have central air, that should take the humidity out. Dragons can tolerate around 60% humidity but much higher than that and your dragon will get respiratory infections. might be a good ideal to buy a digital humidex to measure the tank's humidity, the basking light should help evaporate moisture in the air. I would also remove any dishes of water you may keep in the cage, as water can evaporate from the dish and raise the cage humidity. If your dragon likes to get his water from a dish, instead of u sing one with a wide open top, use a smaller one. A jar lid works well, though it would require frequent refilling, or a small ceramic bowl. The ideal is to decrease the surface area of the water, so less evaporates.
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PHLdyPayne