Metronidazole also sold under the brand name Flagyl and Metrogyle is a potent antibiotic that is used especially for treating bacterial infections of vagina, stomach, skin, joints and respiratory tract. It is part of a family of antibiotics called nitroimidazoles and treats infection by stopping the growth of bacteria and protozoa. It doesn't treat viral infections and hence should not be used for common cold, flu etc as well as vaginal yeast infection.
Tinidazole also sold under the brand names Fasigyn, Tiniba among several other trade names is a potent antibiotic and anti-protozoan drug that is used especially for treating bacterial infections of the vagina. It is also used to treat parasitic infections such as giardiasis or amebiasis.