The miracle antibiotic
Lincomycin was originally developed to treat 'infectious arthritis' (bone and cartilage infections) in pigs. It has the unique ability to penetrate tissue that lacks a good blood supply, which means it can reach infections that other antibiotics cannot. I have been using it since 1974 and I would never be without it in my kennel kit.
I inject lincomycin directly into recalcitrant infections, and it effects a cure in 1 to 3 doses, every time. It does not sting or burn when used as a wound wash (good for infected puncture wounds) and seems to promote faster and cleaner healing. It can be used safely in very young puppies (used to be available as an oral for neonatals, though it should generally not be used orally).
The most dramatic cure it's done for me was the 3 month old puppy who'd been bitten on the head with skull puncture, and had developed an infection inside the skull. We'd been fighting this for two weeks with other antibiotics, without progress. Lincomycin site-injected cured the infection for good in 3 days. The puppy fully recovered.