
You need to have the swab to determine which drug is best. It may have worked for roscoebabe's dog but that does not mean it will for yours.
The only way to know for sure is to have the swab done, the sample from this can then be tested to determine which drugs the bug causing the infection is sensitive to.
When Soli had severe nail infections for months we had to do this - might not sound related but the bug causing it was pseudomonas, which is usually responsible for severe ear infections. Had we not sent a sample off we would not have known precisely which drug to use, and even then it took 2/3 months constant treatment with the right drug to beat it. If we hadn't done the sample, we'd never have guessed pseudomonas and in all likelihood, she'd still be suffering as the normal (and even less used) treatments for nail infections weren't working.