Was a culture taken to target what sort of antibiotics is needed to treat the infection? There are many forms of RI and different types of bacterial RIs specifically. Some antibiotics won't work for certain types.
With my experience with 2 RI rescues, it took a few weeks to notice a significant improvement. Snake metabolism is slower than humans so their reaction to drugs are slower. I take my snakes to a vet school hospital and they gave me 2 months worth of treatment.
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