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EspañolMetronidazole is a generic antimicrobial drug that treats a wide range of bacterial and parasitic infections. Metronidazole belongs to a class of antibiotics called nitroimidazoles, which have a mechanism of action that involves shutting down vital cellular functions in certain bacteria and parasites. It is primarily used to treat infections caused by anaerobic bacteria (bacteria that survive without oxygen) and single-cell parasites such as amoebas and trichomonas. Depending on the type and extent of infection, metronidazole is taken orally as a tablet or capsule, administered as an injection, or applied topically as a cream or gel.
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Metronidazole forms and strengths
Metronidazole is administered in a variety of dosage forms. Generic and brand-name metronidazole come in different forms and include Flagyl (capsules or tablets), Rosadan (topical cream or gel), Nuvessa (vaginal gel), Vandazole (vaginal gel), Metrocream (topical cream), Metrolotion (topical lotion), and Metrogel (topical gel)
Tablet: 250 milligrams (mg), 500 mg
Capsule: 375 mg
Injection: 500 mg/100 milliliter (mL)
Cream: 0.75% (7.5 mg metronidazole per 1 gram (g) of cream)
Gel: 0.75%, 1%
Lotion: 0.75%
Metronidazole dosage for adults
Metronidazole dosage chart |
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|---|---|---|
| Indication | Standard dosage | Maximum dosage |
| Bacterial infections | 15 mg/kg intravenous infusion over 1 hour, then 7.5 mg/kg administered intravenously every 6 hours for 7-10 days or 7.5 mg/kg taken orally every 6 hours for 7-10 days | 4 g per day |
| Pelvic inflammatory disease (PID) | 500 mg taken orally every twice daily for 14 days | Not specified |
| Bacterial vaginosis | 500 mg twice daily for 7 days or One applicatorful (5 grams of 0.75% gel) administered intravaginally once daily for 5 days | Not specified |
| Trichomoniasis | 2 grams taken as a single dose or divided into two 1-g doses or 500 mg twice daily for 7 days (dosage for HIV-infected women) or One 250 mg tablet taken orally 3 times daily for 7 days or One 375 mg capsule taken twice daily for 7 days | Not specified |
| Acute intestinal amebiasis | 750 mg taken orally 3 times daily for 5-10 days | Not specified |
| Amebic liver abscess | 500 or 750 mg taken orally 3 times daily for 5-10 days | Not specified |
| Infection prevention in patients undergoing colorectal surgery | 500 mg or 15 mg/kg administered IV and completed within 1 hour before surgery, then 7.5 mg/kg IV every 6 hours for 2 doses or 1 g taken orally 3 times over 10 hours starting the afternoon and evening before the day of surgery | Not specified |
| Rosacea | Apply and rub a thin layer (0.75% gel, cream, or lotion) to the affected area once in the morning and once in the evening or Apply and rub a thin layer (1% gel, cream, or lotion) to the affected area once daily | Not specified |
Source: Epocrates, Clinical Pharmacology, and DailyMed
Metronidazole dosage for bacterial infections
Metronidazole fights infections caused by bacteria that thrive in oxygen-depleted environments (anaerobic bacteria). Anaerobic infections can develop throughout most parts of the body, such as the abdomen, skin, and genital tract. Metronidazole is often the antibiotic of choice for digestive system infections, such as those caused by Helicobacter pylori (H. pylori) or Clostridium difficile (C. diff). It can also be used to treat skin infections (rosacea or acne), bone and joint infections, central nervous system infections, gynecological infections, some lower respiratory tract infections, blood infections (septicemia), heart infections (endocarditis), and intestinal abscesses due to inflammatory bowel disease (ulcerative colitis or Crohn’s disease). Severe infections may require an initial dose of intravenous metronidazole followed by a regimen of oral or intravenous metronidazole for several days.
Starting dose: 15 mg/kg administered intravenously as a single dose
Standard adult dosage: 7.5 mg/kg administered intravenously or taken orally every six hours
Maximum adult dosage: No more than 4 g per day
Metronidazole dosage for pelvic inflammatory disease
Pelvic inflammatory disease (PID) is often a complication of certain STDs, like gonorrhea or chlamydia, in women. Bacteria can migrate from the vagina or cervix to the upper reproductive organs, such as the uterus, fallopian tubes, or ovaries, and cause PID. Metronidazole is sometimes taken with other antibiotics for severe infections.
Standard dosage for adults and adolescents: 500 mg taken orally twice daily for 14 days
Metronidazole dosage for bacterial vaginosis
Bacterial vaginosis is often caused by an overgrowth of anaerobic bacteria in the vagina. Oral metronidazole is a first-line therapy. However, metronidazole administered as a systemic oral antibiotic can cause side effects such as nausea, diarrhea, constipation, and a metallic taste in the mouth, as well as rare but potentially severe side effects such as peripheral neuropathy (nerve damage), encephalopathy, or aseptic meningitis. To minimize the chance of systemic adverse effects, topical metronidazole gel can be used instead.
Standard adult dosage: 500 mg twice daily for seven days, 2 g taken as a single dose, one applicatorful (5 grams of 0.75% gel) administered intravaginally once daily at bedtime for five days
Metronidazole dosage for trichomoniasis
Trichomoniasis is a common sexually transmitted disease caused by a single-celled parasite. Treatment consists of a single large dose or a seven-day dosing regimen depending on the person’s situation.
Standard adult dosage: 2 grams taken in a single dose or divided into two 1-g doses, 500 mg twice daily for seven days, 250 mg taken 3 times daily for seven days, 375 mg taken twice daily for seven days
Metronidazole dosage for amebiasis (dysentery) and amebic liver abscess
An Amebic infection is a parasitic infection of the intestines, caused by Entamoeba histolytica. This type of infection can lead to diarrhea, cramping, and a collection of pus in the liver called an amebic liver abscess. Metronidazole is FDA-approved to treat amebic infections and amebic liver abscesses.
Standard adult dosage: 750 mg taken orally 3 times daily for five to 10 days for intestinal amebiasis. 500 or 750 mg taken orally three times daily for five to 10 days for amebic liver abscess
Metronidazole dosage for surgical infection prophylaxis
Intravenous metronidazole is sometimes administered before surgery to prevent infections. Metronidazole is typically administered before colorectal surgery, although it can be given to prevent infections from procedures involving the abdomen, gastrointestinal tract, and urogenital tract. For colorectal surgeries, oral metronidazole can be given on the day within an hour before the procedure.
Standard adult dosage for surgical prophylaxis: 500 mg or 15 mg/kg administered IV and completed within one hour before surgery then 7.5 mg/kg IV every six hours for two doses, or 1 g taken orally three times over 10 hours starting the afternoon and evening before the day of surgery
Metronidazole dosage for acne rosacea
Topical metronidazole is used to treat pimples (pustules or papules) caused by an inflammatory rosacea flare-up. Metronidazole 0.75% cream, gel, or lotion is applied twice daily to the affected area. Before application, the skin should be washed with a mild cleanser. Alternatively, oral metronidazole is sometimes prescribed off-label to treat active rosacea. Treatment lasts as long as it takes to reduce inflammation and redness, typically 2 to 10 weeks.
Standard adult dosage for rosacea: Apply and rub a thin layer of 0.75% metronidazole gel, cream, or lotion to the affected area once in the morning and once in the evening, or apply and rub a thin layer of 1% metronidazole gel, cream, or lotion to the affected area once daily
Metronidazole dosage for children
Depending on the condition, metronidazole can be prescribed to children, infants, or newborns depending on the condition being treated. The dose will depend on the infection treated, and it is often based on the child’s weight and age.
| Metronidazole dosage by age/weight | |||
|---|---|---|---|
| Indication | Age | Standard dosage | Maximum dosage |
| Bacterial infections | Neonates | 34 weeks and younger: 7.5 mg/kg/dose PO every 12 hour 35 to 40 weeks: 7.5 mg/kg/dose PO every 8 hours 40 weeks or older: 10 mg/kg/dose PO every 8 hours | Not specified |
| Infants, children, and adolescents | 15 to 50 mg/kg per day by mouth divided every 8 hours | 2,250 mg/day | |
| Bacterial vaginosis | Children | < 45 kg (99 lbs): 15 mg/kg administered orally or intravenously 3 times daily for 7 days | 2,250 mg per day (oral) or 4 g per day (IV) |
| Children and adolescents | > 45 kg: 500 mg taken orally twice daily for 7 days or one applicatorful (5 grams of 1.3% gel) administered intravaginally once daily at bedtime for 5 days (adolescents only) | 2,250 mg per day (oral) or 4 g per day (IV) | |
| Trichomoniasis | Children | < 45 kg: 15 mg/kg administered orally 3 times daily for 7 days | 2,250 mg per day (oral) or 4 g per day (IV) |
| Children and adolescents | > 45 kg: 2 g taken as a single dose or divided into 2, 1-g doses, or 500 mg taken twice daily for 7 days | 2,250 mg per day (oral) or 4 g per day (IV) | |
| Amebic dysentery or amebic hepatic abscess | Infants, children, and adolescents | 11.6–16.6 mg/kg administered orally or intravenously every 8 hours for 7-10 days | 2,250 mg per day (oral) or 4 g per day (IV) |
| Surgical prophylaxis | Infants, children, and adolescents | 15 mg/kg IV infusion completed one hour before surgery For colon procedures: 15 mg/kg given in 3 oral doses with neomycin over 10 hours starting the afternoon and evening before the procedure | 1 g per dose if given orally 500 mg per dose if given IV |
Metronidazole dosage restrictions
People with a known hypersensitivity to metronidazole should not be given the drug. Metronidazole doses may be adjusted in people with severe impairment of liver function, but mild to moderate hepatic impairment may require only monitoring for adverse effects.
Renal impairment may not affect dosing, but patients on intermittent hemolytic dialysis may receive a supplementary dose following dialysis. Other medical conditions—particularly blood dyscrasias (“disorders”) or Cockayne syndrome—may not require dose adjustments, but patients will be monitored for increased side effects.
Metronidazole dosage for pets
Metronidazole is not approved for use in animals, but veterinarians often prescribe a veterinary formulation of metronidazole to treat bacterial or parasite infections, particularly giardiasis, as well as inflammatory bowel disease in dogs, cats, and other animals.
Doses are usually determined by the animal’s weight. Metronidazole may be administered orally one to three times a day for anywhere from three to 10 days depending on the medical condition being treated. For pet fish, metronidazole can be prescribed as a powder to add to the aquarium in two doses separated by 48 hours.
How to take metronidazole
Metronidazole is taken orally, applied topically, or given as an intravenous infusion.
Take the medicine as directed.
Take the full course of medicine even if symptoms seem to improve early. The entire multi-day regimen is required to fully eradicate the infection.
Metronidazole is typically taken in one to four doses a day. Space the doses as evenly as possible across the day or as directed by your doctor.
Tablets or Capsules
The tablets or capsules can be taken with or without food as directed by your doctor. If you experience an upset stomach after taking the medication, you can take the next doses with a meal or snack.
Swallow the tablet or capsule whole with a full glass of water. Do not crush, break, or chew it.
Lotion, gel, or cream
Wash the affected skin area with a mild cleanser.
Apply and gently rub in a thin layer of the metronidazole lotion, gel, or cream to the affected area.
Vaginal gel
Metronidazole can be administered using an applicator that is either prefilled or manually filled from a tube before use.
When filling an empty applicator (Vandazole or Perrigo metronidazole gel), attach and screw in the open end of the applicator to the tube. Squeeze in the medicine until the applicator is full.
If using a prefilled applicator like Nuvessa, remove the orange cap before insertion.
In a relaxed position, preferably on your back, gently insert the applicator.
Slowly and fully press the plunger.
Remove the applicator and dispose of it properly. Do not use applicators for more than one dose.
Consult a healthcare provider for instructions on appropriate application before use.
Metronidazole dosage FAQs
Metronidazole vs. metronidazole XR/ER: What’s the difference in doses?
Extended-release, or ER formulations of drugs typically release the drug throughout the day. Extended-release formulations are usually dosed less times throughout the day versus several times per day with immediate-release formulations. Extended-release metronidazole, originally available as Flagyl ER extended-release tablets, is no longer sold in the United States.
What happens if I miss a dose of metronidazole?
Take a dose as soon as it’s remembered. However, if it is almost time for the next dose, skip the missed dose and take the next scheduled dose on time. Do not take extra medicine to make up for a missed dose.
Can you overdose on metronidazole?
A metronidazole overdose is potentially hazardous and may require emergency medical treatment. A metronidazole overdose typically causes nausea, vomiting, and loss of coordination. Treatment for overdose will usually consist of supportive measures and managing symptoms. Call a poison control center or seek immediate medical attention if you suspect an overdose.
What happens when you mix metronidazole and alcohol?
Metronidazole acts like disulfiram, a medication used to treat alcohol use disorder. Like disulfiram, metronidazole causes a severe reaction to alcohol or propylene glycol, a common ingredient in foods and medicines, causing abdominal pain, abdominal cramps, nausea, vomiting, headache, flushing, and other adverse effects. For this reason, people taking metronidazole should avoid alcohol and any foods or other substances containing propylene glycol for the entire course of treatment and up to three days after treatment ends.
Is it safe to take metronidazole during pregnancy?
There are not enough studies on people to determine if metronidazole is safe to take during pregnancy. Doctors and other healthcare professionals, however, are cautioned to avoid prescribing metronidazole during the first trimester of pregnancy. As with all medications, pregnant women should discuss the risks and benefits of taking metronidazole with a physician or other healthcare provider.
During lactation, metronidazole does pass into breast milk and could harm a breastfeeding baby. A healthcare provider may suggest avoiding nursing while taking metronidazole and up to three days after stopping treatment.
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