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EspañolFlagyl is a brand-name antimicrobial medicine approved by the FDA to treat a range of bacterial infections that affect the skin, digestive system, respiratory tract, liver, heart, blood, joints, bone, teeth, brain, reproductive organs, and genitals. The active ingredient, metronidazole, belongs to the nitroimidazole drug class that works by shutting down vital cellular processes in anaerobic bacteria, bacteria that thrives in oxygen-free environments.
In addition to its antibacterial effects, Flagyl also eradicates infections caused by single-cell parasites such as trichomonas, amoebas, and giardia. Flagyl is taken as a film-coated tablet or capsule for 1 to 10 days, or possibly longer for more serious or extensive infections.
RELATED: Learn more about Flagyl | Get Flagyl discounts
Flagyl forms and strengths
Flagyl is only taken orally as a capsule or tablet. Metronidazole, however, comes in other dosage forms including intravenous injections, creams, lotions, and gels.
Tablet: 250 milligrams (mg), 500 mg
Capsule: 375 mg
Flagyl dosage for adults
| Flagyl dosage chart | |||
|---|---|---|---|
| Indication | Starting dosage | Standard dosage | Maximum dosage |
| Bacterial infections | 15 mg/kg metronidazole intravenous infusion or 7.5 mg/kg (500 mg for a person weighing 70 kg/154 pounds) taken every 6 hours for 7-10 days | 7.5 mg/kg (usually 500 to 750 mg) taken every 6 hours for 7-10 days | No more than 4 grams daily |
| Pelvic inflammatory disease (PID) | 500 mg every 12 hours for 14 days | 500 mg every 12 hours for 14 days | Not specified |
| Bacterial vaginosis | 2 grams taken as a single one-day dose or 500 mg every 12 hours for 7 days | 500 mg every 12 hours for 7 days | Not specified |
| Trichomoniasis | 2 grams taken in a single dose or divided dose or One 250 mg tablet taken 3 times per day for 7 days or One 375 mg capsule taken twice per day for 7 days | One 250 mg tablet taken 3 times per day for 7 days or One 375 mg capsule taken twice per day for 7 days | Not specified |
| Acute intestinal amebiasis | 750 mg taken every 8 hours for 5-10 days | 750 mg taken every 8 hours for 5-10 days | Not specified |
| Amebic liver abscess | 500–750 mg taken every 8 hours for 5-10 days | 500–750 mg taken every 8 hours for 5-10 days | Not specified |
| Infection prevention before surgery | 1000 mg taken 3 times a day before surgery | 1000 mg taken 3 times a day before surgery | Not specified |
Source: Epocrates and DailyMed
Flagyl dosage for bacterial infections
Flagyl treats a wide range of infections caused by anaerobic bacteria, which is bacteria that can live without oxygen. Gastrointestinal infections including Helicobacter pylori (H. pylori) and Clostridium difficile infections, skin infections including acne and rosacea, some respiratory infections, endocarditis (infections of the outer heart), septicemia (bacterial blood poisoning), dental and oral infections, abdominal infections, bone infections, joint infections, brain and spinal cord infections, and gynecological infections are commonly caused by anaerobic bacteria.
Metronidazole is also used to heal intestinal abscesses caused by Crohn’s disease or ulcerative colitis. Many infections will be treated with a combination of metronidazole and another antibiotic, such as amoxicillin. A severe infection may be initially treated with a large intravenous injection of metronidazole, the active ingredient in Flagyl, followed by daily dosing with Flagyl.
Standard adult dosage: 7.5 mg/kg (usually 500 to 750 mg) taken every six hours for seven to 10 days
Maximum adult dosage: No more than 4 grams per day
Flagyl dosage for pelvic inflammatory disease
Pelvic inflammatory disease is a type of anaerobic bacterial infection. It occurs when a sexually transmitted bacterial infection migrates to the uterus, fallopian tubes, and ovaries.
Standard dosage for adults and adolescents: 500 mg every 12 hours for 14 days
Flagyl dosage for bacterial vaginosis
Bacterial vaginosis occurs when anaerobic bacteria normally living in the vaginal tissues grow out of control. Treatment consists of Flagyl daily doses over seven days or a large single dose taken on one day. Alternatively, bacterial vaginosis can be treated with topical metronidazole available generically or under the brand names Vandazole and Nuvessa.
Standard adult dosage: 500 mg every 12 hours for seven days or 2 grams taken as a single one-day dose
Flagyl dosage for trichomoniasis
Trichomoniasis is a common sexually transmitted disease caused by a single-celled parasite called trichomonas. Both men and women can get infected with trichomonas, but men typically do not experience symptoms. To avoid spreading the infection, most people will be treated with one or two high Flagyl doses in a single day to quickly eradicate the infection. Alternatively, the seven-day regimen helps prevent re-infection until the person’s sexual partners also receive treatment.
Standard adult dosage: One 250 mg tablet taken three times per day for seven days, one 375 mg capsule taken twice per day for seven days, or 2 grams taken in a single or divided one-day dose
Flagyl dosage for amoeba infections
Flagyl is approved for amoeba infections of the intestines (amebiasis) and liver (amebic hepatic abscess). Because metronidazole kills amoebas only in their growing stage, other drugs are required to kill the amoebas at other stages in their life cycle.
Standard adult dosage: 750 mg taken every eight hours for 5 to 10 days for intestinal amebiasis or 500–750 mg taken every eight hours for 5 to 10 days for amebic liver abscess
Flagyl dosage for colorectal surgical infection prophylaxis
Metronidazole combined with other antibiotics is administered preceding abdominal or gynecological surgery to prevent anaerobic infections. Although it is typically given as an IV infusion one hour before surgery, treatment guidelines call for administering oral metronidazole on the day preceding colon procedures.
Standard adult dosage: 1000 mg given in three oral doses (3 grams total) 19, 18, and 9 hours preceding surgery
Flagyl dosage for children
Depending on the condition, Flagyl can be prescribed to children as young as newborns. The recommended dose will depend on the medical condition treated.
| Flagyl dosage by age/weight | |||
|---|---|---|---|
| Indication | Age | Standard dosage | Maximum dosage |
| Bacterial infections | Newborns < 2 months old and < 1.2 kg (2.6 lbs) | 7.5 mg/kg administered every 48 hours | Not specified |
| Newborns 1.2 kg or greater and < seven days old | 7.5–15 mg/kg per day divided into one or two doses | Not specified | |
| Newborns 1.2 kg or greater and at least seven days old | 7.5–15 mg/kg given every 12 hours | Not specified | |
| Infants, children, and adolescents | 7.5 mg/kg taken every six hours | 4 g per day | |
| Bacterial vaginosis | Adolescents or preadolescents < 45 kg (99 lbs) | 15 mg/kg divided into 2 daily doses administered every 12 hours for 7 days | 1 g daily |
| Adolescents or preadolescents > 45 kg (99 lbs) | 500 mg taken every 12 hours for 7 days taken as a single 1x dose | Not specified | |
| Trichomoniasis | Preadolescents < 45 kg | 45 mg/kg divided into 3 daily doses administered every 8 hours for 7 days | 2 g daily |
| Adolescents or preadolescents > 45 kg | One 250 mg tablet taken 3 times per day for 7 days, one 375 mg capsule taken twice per day for 7 days, or 2 grams taken in a single or divided one-day dose | Not specified | |
| Amebic dysentery or amebic hepatic abscess | Infants, children, and adolescents | 35–50 mg/kg per day taken in 3 doses divided every 8 hours for 7 to 10 days | 2,250 mg per day |
| Surgical prophylaxis | Infants, children, and adolescents | 15 mg/kg given in 3 doses 19, 18, and 9 hours preceding surgery | Not specified |
Flagyl dosage restrictions
People with hypersensitivity to metronidazole will not be given Flagyl. Mild to moderate impairment of liver function will not affect Flagyl dosing, but those with a severe liver impairment will require Flagyl doses to be reduced by half. Renal impairment (kidney problems) does not affect Flagyl doses, but supplemental doses may be given following dialysis.
Flagyl dosage for pets
Metronidazole is not approved for use in animals, but a veterinarian may prescribe this drug to a pet to treat bacterial or protozoal infections such as giardiasis, trichomoniasis, or balantidiasis, or inflammatory bowel disease. Dose amounts will depend on the animal’s weight. Doses will be given orally one to three times a day for three to ten days depending on the medical condition being treated.
How to take Flagyl
Flagyl is taken orally as a capsule or tablet.
Take the medicine as directed.
Take the medicine over the full course of treatment even if symptoms go away. The entire multi-day regimen is required to ensure the infection is eradicated.
Space the doses as evenly as possible across the day.
Tablets
Take the tablet.
Swallow the tablet whole with a full glass of water. Do not crush, break, or chew it.
Capsules
The capsules can be taken with or without food.
Swallow the capsule whole with a full glass of water.
Flagyl dosage FAQs
What happens if I miss a dose of Flagyl?
A missed dose should be taken as soon as it is remembered. However, if it is nearly time for the next dose, it should be skipped and the next scheduled dose should be taken. An extra Flagyl dose should never be taken to make up for a missed dose.
What interacts with Flagyl?
As with all medicines, Flagyl may cause possible drug interactions that will limit taking other types of prescription drugs. People taking Flagyl should not drink alcohol or take disulfiram (a drug that treats alcohol use disorder) during treatment. Metronidazole has been reported as causing psychotic reactions in people taking disulfiram.
Metronidazole can increase the toxicity of some drugs, such as busulfan and lithium, so therapies may have to be adjusted. The blood-thinning properties of warfarin and similar anticoagulant drugs are increased by metronidazole, so the dosages will need to be modified.
Some drugs, such as cimetidine (an ulcer drug), interfere with the body’s ability to eliminate metronidazole, leading to an increase in the plasma concentrations of metronidazole. As a result, the likelihood and severity of temporary side effects, such as nausea, diarrhea, constipation, and a metallic taste in the mouth, can increase. These interactions also increase the likelihood of severe adverse effects such as peripheral neuropathy (nerve damage), encephalopathy, or meningitis.
Dosages will also need to be adjusted when metronidazole is taken with prescription drugs, such as phenytoin (a seizure medication), that speed up the body’s elimination of metronidazole.
What happens when you mix Flagyl and alcohol?
Alcohol and any foods or medicines containing propylene glycol (a type of alcohol) must be avoided when taking Flagyl. Alcohol cannot be safely consumed for at least three days after stopping Flagyl. In some people, metronidazole causes a severe adverse reaction to alcohol or propylene glycol that includes abdominal cramps, abdominal pain, nausea, vomiting, and headache.
Is it safe to take Flagyl during pregnancy?
There are not enough studies to determine if it is safe for a pregnant woman to take metronidazole. Doctors and other healthcare professionals, however, will generally avoid prescribing metronidazole during the first trimester of pregnancy.
Because of potential cancer risks for babies, a healthcare provider may suggest avoiding nursing while taking metronidazole. Breast milk could be pumped during this period to maintain lactation, but the milk should be discarded. Breastfeeding should not resume until three days after the last dose of Flagyl has been taken.
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