Rxlist.com provides dosage guidelines based on gender, pregnancy status and length of treatment, including dosages ranging from 250 milligrams to 2 grams. Flagyl is often used to treat trichomoniasis confirmed by laboratory findings, according to RxList.
When health care providers decide to only treat a patient for one day, they prescribe 2 grams of Flagyl given as a single dose or in two divided doses within the same day. However, a seven-day course consists of a much lower dose of Flagyl per day. A seven-day dosage is 250 milligrams of Flagyl three times a day for a week, as indicated by RxList.