how closly do you watch the snake? watch it after it's been given the meds to make sure it's not coming back up, and is this a big snake? if that's the case ask your vet for syringes with thin needles so you can inject meds into the food, a big snake will be fine to eat a pinky mouse everyother day, or however often you have to give them meds, that's been injected with the medicine. Most to worry about is the snake constricting the meds out before eating it, hence the small needle. If that fails last best thing you can do is have the vet give you a syringe with a tube so you put the meds directly into the stomach. As a last resort you can have the vet give you injections, if he's competent he'll know it has to be diluted because injected batryl causes necrosis and painful sores, however diluting will prevent that. But absolutely get a culture, i recommend a lung wash, much more expensive but it will give you way more accurate results, and in the end you'll spend less.