Amikacin itself will not cause dehydration in an animal. The reason that animals being treated with amikacin require proper hydration is that the majority of the drug is excreted through the kidneys. Aminoglycoside class antibiotics can damage the cells of the filtration system in the kidneys and adequate movement of fluids through this system will keep the excreted drug moving on through the kidneys. As long as fresh water is always available and humidity is moderate to high, there is little chance of an issue. I have used amikacin and tobramycin in blood pythons on numerous occasions in the 1980’s and 1990’s with no changes in water access and had no problems. Just make sure to keep it fresh.
No amount of extra water above what they would normally intake would be of any consequence, as they can only process water through the kidneys at a given rate. The issues occur when you have any animal that is already dehydrated for some reason, or is too weak to drink from a standard water bowl. Under these conditions, what you recommended is absolutely correct in order for the animal to be able to maintain hydration, and allow for proper excretion of the drug through the kidneys. Additionally, make sure that blood pythons receive half of the standard python dosage of any aminoglycoside. They are more sensitive to this class of antibiotics and no amount of hydration will protect them from an overdose and kidney damage.
Kelly