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What Factors Affect Flagyl® Dosage?

By Canaan Downs
Updated May 17, 2024
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The generic drug metronidazole, sold under the brand name of Flagyl®, is an antibiotic considered to be a specific treatment for trichomoniasis, amoebiasis and anaerobic bacterial infections. Adjustments must be made to the standard dose according to the age, condition, treatment duration, reproductive status, liver health, and level of kidney function of the patient. Due to the considerable variance between patients in the pharmacokinetics of the drug, individual Flagyl® dosage must be tailored to the response of each patient. In particular, the level of the drug in the serum of elderly patients may need to be regularly monitored to determine if adjustments must be made to their Flagyl® dosage.

When the medication is being used to treat patients suffering from trichomoniasis, it may be given in either a single- or seven-day course of treatment. While there is some evidence that the seven-day course of treatment may have a higher success rate, the shorter course of treatment ensures patient compliance if given under supervision and reduces the risk of developing further resistance to the drug. Patients receiving the drug for seven days should be given a Flagyl® dosage of 250 mg three times per day for the duration. Patients receiving the drug for a single day may receive their 2 g Flagyl® dosage in either one dose or in two 1 g doses spread throughout the course of the day. It is important that any potentially infected sexual partners also receive treatment, lest reinfection occur.

Due to the risks of the medication, subsequent courses of treatment should not be undergone for four to six weeks from the conclusion of the previous treatment. The patient's levels of total and differential white blood cells should be monitored before and after repeat courses. If laboratory results are negative for trichomoniasis or if the patient is in the first trimester of pregnancy, alternative treatments should be used. In pregnant patients where alternative treatments have been ineffective, the seven-day course of treatment should be followed, as the higher single day Flagyl® may cross into the fetal blood supply.

When Flagyl® is used in the treatment of adult patients with acute intestinal amoebic infections, such as amoebic dysentery, 750 mg of the drug should be administered three times daily for a period of five to ten days. Adult patients suffering from amoebic liver abscesses may receive a Flagyl® dosage of between 500 and 750 mg three times daily for the same period of time. When treating pediatric cases of amoebiasis, the appropriate Flagyl® dosage is between 35 and 50 mg per 2.2 lbs (1 kg) of body weight, given in three divided doses for ten days.

The medication is also used in the treatment of serious anaerobic bacterial infections. Following the conclusion of intravenous treatment with Flagyl®, the drug is usually administered orally for no fewer than seven to ten days. The typical recommended Flagyl® dosage for adults is 7.5 mg per 2.2 lbs (1 kg) of body weight every six hours, although no more than 4 g should be given within a 24-hour period.

Regardless of the condition, patients with reduced liver function should receive a lower Flagyl® dosage, as should patients with reduced kidney function. These patients should have their plasma levels of the drug monitored to ensure that the dosage is correct. Patients undergoing dialysis, however, may not require dosage adjustment, as Flagyl® is rapidly removed by the procedure.

WiseGEEK is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.

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