Flagyl is a drug used to treat a vast array of infections. Specifically it targets bacteria, known as anaerobic bacteria, which do not use oxygen to grow. This makes it a highly useful drug for quite a lot of infections, ranging from bacterial vaginosis and peritonitis, to H. pylori infection and pseudomembranous colitis. It works by disturbing the synthesis of DNA inside anaerobic organisms. Flagyl has numerous interactions, some of which cause nausea and vomiting, such as that which occurs with alcohol.