Metronidazole acts as an antibiotic as well as an anti-parasitic treatment. I've used it with great results.
http://www.tomgriffin.com/aquasource/ipmetro.html
"Metronidazole was originally developed to combat the parasites that cause amebiasis and giardiasis in humans. To put it kindly, both conditions wreak havoc on the human excretory system. To this day, the drug remains useful for both human and veterinary applications. It possesses both antiprotizoal and antibacterial qualities. To alleviate multiplying parasitic populations due to the stress of capture and transport, most imported reptiles (wild caught) receive a metronidazole/panacure cocktail upon arrival, if not before export. Many keepers of more expensive or delicate fish including discus, apistogramma, or wild caught cichlids consider metronidazole a "must have" for their fish medicine cabinet"