Is Metronidazole Safe in Pregnancy and Breastfeeding?

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Pregnant women often need to take medications for various health conditions. However, with a baby developing inside, it is understandable to have concerns about medication safety.

One common medication prescribed during pregnancy is the antibiotic metronidazole. This drug treats many bacterial and parasitic infections, such as bacterial vaginosis.

If your doctor recommended this drug, you’ll likely have questions. Is metronidazole safe in pregnancy and for unborn babies? What are the potential risks or side effects? When do the benefits outweigh any risks? Learn about the safety of the antibiotic metronidazole for pregnant women and whether it’s safe during pregnancy.

Is Metronidazole safe in Pregnancy

Metronidazole goes by the brand names Flagyl, Metro, or Protostat. It is an antibiotic that fights certain bacterial and parasitic infections in the body. Metronidazole works by disrupting the DNA of bacteria cells, effectively killing them.

Doctors often prescribe metronidazole for pregnant patients to treat:

  • BV – a common vaginal infection
  • Ulcers caused by Helicobacter pylori bacteria
  • Gum infections
  • Diverticulitis
  • Bacterial and parasitic infections elsewhere in the body

Metronidazole treats infections from anaerobic bacteria, which thrive without oxygen. It’s also effective against Trichomonas vaginalis, a parasite that causes trichomoniasis, and other parasitic protozoans like Giardia intestinalis and Entamoeba histolytica.

BV involves an overgrowth of certain bacteria like Gardnerella vaginalis in the vagina. Although BV causes discharge and odor, it is not considered an STD. However, having BV while pregnant raises the risk of preterm birth.

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What Are the Side Effects of Metronidazole?

The most common side effects of metronidazole affect the digestive system. Up to 12% of people taking this medication experience:

  • Nausea
  • Vomiting
  • Diarrhea
  • Abdominal cramping
  • Metallic taste in the mouth
  • Metronidazole may also cause:
  • Yeast infections – because it kills good bacteria in the vagina
  • Headache
  • Drowsiness
  • Dizziness
  • Dry mouth
  • Dark urine
  • Rarer side effects include:
  • Numbness or tingling in the hands or feet
  • Seizures
  • Depression
  • Swelling of the tongue
  • Fever with white spots in the mouth
  • Vaginal irritation or dryness

Studies show oral metronidazole taken at normal therapeutic doses is generally well tolerated with no difference in side effects compared to a placebo. Topical vaginal preparations also have minimal risks of irritation.

However, high doses or long-term use increase the likelihood of peripheral neuropathy (nerve damage in the extremities). Prolonged use of oral metronidazole also appears to raise the threat of certain cancers, according to experimental studies on rats and mice.

Read also: Can Metronidazole Treat Chlamydia?

What Are the Side Effects of Metronidazole?

A few special precautions apply when taking metronidazole:

Do NOT drink alcohol during treatment or for three days after finishing metronidazole. This combination provokes severe nausea, vomiting, cramps, flushing, and headaches. The disulfiram reaction disrupts the metabolism of alcohol and the drug. Metronidazole interferes with medications like blood thinners, seizure drugs, and lithium. Inform your doctor about any other medications you take.

Use sun protection as this antibiotic increases sun sensitivity. You can wear sunscreen and protective clothing outside. Metronidazole may temporarily turn urine darker or reddish-brown. This harmless discoloration is not cause for alarm. Take the entire course as prescribed, even if you feel better. Stopping treatment early allows bacteria to regrow and develop resistance to the antibiotic.

Do I Need a Prescription for Metronidazole?

Yes, you need a doctor’s prescription to get metronidazole. Self-medicating with antibiotics is never recommended. Your doctor will determine if this antibiotic will effectively treat your illness. They will also prescribe the proper dose and duration based on your health profile.

What Is the Dosage for Metronidazole?

A typical oral metronidazole dosage for bacterial vaginosis in pregnant women is 400-500 mg, taken twice daily for 5-7 days. For trichomoniasis, the (CDC) Centers for Disease Control and Prevention recommends a single 2 g oral dose.

Topical vaginal gel or cream preparations of metronidazole are also commonly prescribed at 0.75%. For these topical treatments, standard regimens are once daily intravaginal application for 5 consecutive days or twice daily for 3 days.

Your doctor will adjust the dose higher or lower based on the severity of the infection. The normal maximum daily dose is 4 grams. Taking metronidazole with meals can reduce side effects like nausea.

Metronidazole comes in four forms:

  • Tablets – Are available in 250 mg and 500 mg doses
  • Extended-release tablets – Have a 750 mg dose released slowly over time
  • Topical creams/gels/lotions – Applied vaginally or to the skin
  • Intravenous (IV) – Administered by injection in hospitals

Oral tablets or topical vaginal gels are usually prescribed for pregnant patients. IV metronidazole is reserved for severe systemic infections unresponsive to oral treatment.

Who Should Not Take Metronidazole?

Specific individuals should avoid metronidazole, including:

  • Those with a history of severe allergic reactions to metronidazole or other nitroimidazole drugs
  • People with severe liver disease, which impairs metronidazole metabolism
  • Those currently taking or who recently took disulfiram (Antabuse) medication for alcoholism

Metronidazole in Pregnancy

Is Metronidazole safe in pregnancy? Metronidazole is among several antibiotic choices considered generally safe for pregnant women by major health organizations. The benefits often outweigh any theoretical risks to the fetus when the mother has a dangerous infection requiring prompt treatment.

However, some conflicting studies create debate around whether metronidazole is entirely safe during pregnancy. Let’s explore what the latest research says.

Metronidazole and Breastfeeding

Small amounts of metronidazole can pass into breast milk after a mother takes the antibiotic. However, the amount is significantly less than in the mother’s bloodstream.

Short-term or low-dose metronidazole treatment is considered safe with breastfeeding. However, prolonged high-dose use could lead to the accumulation of the drug in the infant.

Potential infant side effects include diarrhea or yeast infections like thrush. Some experts recommend nursing mothers temporarily pump and discard breast milk during metronidazole therapy and for 12-24 hours after finishing the medication. However, the data on harm is inconclusive, and opinions vary among researchers.

Metronidazole Pregnancy Warnings

Metronidazole can cross the placenta and enter fetal circulation rapidly after a pregnant woman takes the drug. Yet, animal studies did not reveal evidence of teratogenic effects or harm to fertility at typical therapeutic doses.

Several published studies involving pregnant women who took metronidazole found no increase in congenital disabilities. However, a few older studies suggested a potential link between metronidazole and cleft lip and palate. Regardless, later studies did not confirm this association.

Overall, research does not indicate metronidazole elevates the baseline risk for miscarriage, congenital abnormalities, or problems with development. Nonetheless, extensive controlled studies in human pregnancy are still lacking.

Metronidazole Breastfeeding Warnings

Metronidazole is excreted at low levels in breast milk. Concerns stem from animal studies showing mutagenicity, genotoxicity, and potential carcinogenic effects of chronic high-dose metronidazole.

However, infants receive breast milk well below pediatric oral doses for treating infant infections. No harm has been conclusively reported, but monitoring of infant stool patterns is recommended.

Is Metronidazole safe in Pregnancy

Based on current evidence, most experts consider oral and topical metronidazole safe for short-term use during the final two trimesters of pregnancy since its benefits justify the low risks.

However, some doctors remain cautious about first-trimester use, given the lack of extensive controlled studies in pregnant women. Recommendations usually suggest avoiding metronidazole early in pregnancy unless it’s the only suitable option to treat a severe infection. Many leading health agencies and obstetric associations designate metronidazole as pregnancy category B, meaning:

Animal studies show no risk, but controlled studies in pregnant women are unavailable. So metronidazole remains controversial but is approved for treating symptomatic vaginal infections and other dangerous illnesses during pregnancy when indicated.

Can Taking Metronidazole During Early Pregnancy Increase the Risk of Miscarriage?

Based on current evidence, oral metronidazole in early pregnancy does NOT substantially increase the risk of miscarriage.

A 2007 Danish study initially observed a weak association between metronidazole use before week 10 and miscarriage. However, a 2010 re-analysis of the data found the slight elevation was likely due to confounding factors. Several other studies found no link between metronidazole and miscarriage risk. Still, given the lack of large controlled trials, some experts advise cautious non-essential use in the 1st trimester until more conclusive human data is available.

Can Taking Metronidazole During Pregnancy Cause Birth Defects?

According to the best current research, taking metronidazole during pregnancy does NOT appear to advance the risk of birth disabilities meaningfully.

No human studies show solid evidence of teratogenic or fetotoxic effects. Most experts consider oral and topical metronidazole safe when used briefly during the later stages of pregnancy.

Monitoring fetal development with a 20-week ultrasound scan for anomalies is recommended regardless of medication exposure. Discuss any concerns about medications during pregnancy with your obstetrician.

When To See a Doctor

Contact your doctor right away if you experience:

  • Severe persistent vomiting or diarrhea
  • Abdominal pain or cramping
  • Tingling or numbness in fingers or toes
  • Fever over 101°F
  • Dark urine
  • Yellowing skin or eyes
  • Rash or itching
  • Swelling of face, throat, tongue or lips
  • Breathing problems

Mild transient side effects like nausea or loose stools often resolve independently. But call your doctor if symptoms worry you or don’t improve within 2-3 days. Prompt medical attention helps prevent complications from infections or medication reactions.

Read also: Metronidazole for Tooth Infection


As available safety data shows, metronidazole is a relatively low-risk antibiotic during pregnancy. Many vaginal infections like BV require prompt treatment in expecting mothers to prevent preterm birth. In these cases, the benefits of short-term metronidazole use often outweigh the low risks.

Talk to your obstetrician about your health status, pregnancy stage, and treatment options. You can use antibiotics like metronidazole to protect your health and your developing baby. Stay in close contact with your doctor while taking any medication during pregnancy. You should also report any concerning side effects immediately.

Frequently Asked Questions

Yes. Pregnant women can take metronidazole but with caution. Metronidazole is considered safe for short-term use in the last two trimesters of pregnancy when the benefits outweigh the potential risks. You should avoid metronidazole in the 1st trimester unless necessary. Metronidazole commonly treats bacterial vaginosis, parasitic infections, pelvic inflammatory disease, and other bacterial infections during pregnancy.

Potential risks of metronidazole during pregnancy are low but include:

  • Increased nausea, vomiting, diarrhea, or stomach pain
  • Yeast infections
  • Headache, dizziness, or drowsiness
  • Metallic taste in the mouth
  • Dark urine
  • Sensitivity to sun
  • Nerve damage if taken long-term or at high doses
  • Risks from untreated infection if not taken when needed

There are also unproven concerns based on animal studies about mutagenicity, genotoxicity, or carcinogenicity. However, the doses in humans are much lower, and risks remain theoretical. Studies have found no solid evidence of increased congenital disabilities, miscarriage risk, or harm to the developing fetus from short-term use.

The typical oral dose of metronidazole during pregnancy is 400-500 mg, taken twice daily for 5-7 days. For BV, a 7-day course is often prescribed. For trichomoniasis, a single 2 g oral dose may be recommended. Your doctor will prescribe the appropriate therapeutic dosage and duration based on your infection severity and type. Always take the entire course as directed.

Small amounts of metronidazole can cross the placenta and enter the fetal bloodstream. However, studies have not found evidence of teratogenic or harmful effects on the developing baby when the drug is used for short durations at typical doses during the 2nd/3rd trimester. Preterm birth is more likely if infections like BV go untreated during pregnancy. Talk to your doctor about monitoring fetal development.

Yes, you can take metronidazole during pregnancy to treat certain infections when the benefits outweigh the risks in your doctor’s judgment. You should avoid metronidazole during the 1st trimester unless critical.

Short-term oral or vaginal metronidazole use in the 2nd/3rd trimester is generally considered safe. Have an honest discussion with your obstetrician about your infection and treatment options. Discuss if metronidazole is appropriate for you based on your health status, pregnancy stage, infection severity, and other options. Follow their recommendations closely.

The content on Doctor Alexa’s blog is reviewed by Advanced practice registered nurses or pharmacist and is intended for educational purposes only. This information should not be relied upon as professional medical counsel. Be sure to always consult with your physician about the dangers and benefits of any medication, treatment or procedure.

You shouldn’t wait to see the doctor for simple health needs.