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Metronidazole Side Effects

Metronidazole Side Effects

The antibiotic metronidazole is used to treat infections caused by certain parasites or bacteria. This article describes the uses and side effects of this drug.
Leena Palande
Last Updated: Mar 13, 2018
Anaerobic bacteria which can thrive in the abdomen, even with little oxygen, can cause bacterial peritonitis, liver abscesses, and abscesses of the ovaries and the fallopian tubes. Abdominal pain and diarrhea can be experienced due to intestinal parasites like giardia lamblia and amoeba. Vaginitis is caused by the trichomonas, vaginal parasites. The antibiotic metronidazole has been found useful in inhibiting some of the processes within the bacterial cells and the parasites, leading to their death. The antibiotic is available under the brand name Flagyl. Like all other antibiotics, metronidazole side effects can be experienced if the instructions of the doctor regarding the dosage are not followed properly.


500 mg and 250 mg tablets of Metronidazole are often used to treat various bacterial and protozoal infections. The other forms like 750 mg (extended release) tablets, 375 mg capsules, injections, creams, lotions, and gels are also very common. The cream or gel works great for acne rosacea while the vaginal gel is recommended for vaginitis. Following is a list of diseases and disorders for which this antibiotic is prescribed by the doctor:
  • Abscesses in the pelvis, abdomen, and brain caused by susceptible anaerobic bacteria
  • Amoebic dysentery (severe infection of the colon resulting in bloody diarrhea)
  • Amoebic liver abscess
  • Bacterial vaginosis
  • Presence of carriers of trichomonas, which are asymptomatic
  • Helicobacter pylori infection leading to stomach or intestinal ulcers
  • Colon infection caused by a bacterium called C. difficile
  • Parasitic infections like 'giardia infections' of the small intestine
  • Trichomonas vaginal infections
  • Pelvic inflammatory disease
  • Periodontal diseases
Side Effects

Mostly, mild side effects like nausea, stomach pain, loss of appetite, headache, metallic taste in the mouth, change in the color of the urine are noticed by the patients after taking Metronidazole. The antibiotic is normally well tolerated by all types of patients; however, some patients may notice skin rash, vomiting, diarrhea, constipation, dry mouth, etc. If more severe side effects like dizziness or unsteadiness, seizures, extreme mood swings, increased irritability, numbness or tingling sensation in hands or feet, or pain while urinating are noticed, then one should immediately contact the doctor. Side effects like change in vision or pain in the eye, constant fever, sore throat, unusual bleeding or bruising, unbearable stomach pain, blood or mucus in stool, persistent nausea or vomiting need prompt medical attention. Those who are allergic to the drug may experience skin rash, shortness of breath, itching or swelling in the face, tongue, or throat, dizziness, etc. Like peripheral neuropathy, encephalopathy, and aseptic meningitis are some of the rare side effects of the medicine. In such cases, the use of this antibiotic has to be stopped immediately. It can also interact with other medications and cause certain side effects. So, one should inform the doctor about the routine medications and other diseases or disorders before taking this antibiotic. Serious reactions may take place if this antibiotic is taken with certain other drugs. It can lead to seizures, kidney failure, high heart rate, etc.

While taking metronidazole, the consumption of alcohol should be avoided since it can result in some severe health complications. Such a combination increases the risk of seizures, liver cirrhosis, breathing difficulty, hepatitis B or C, increase in heart rate and blood pressure levels, etc. The antibiotic cannot control viral infections like common cold and flu. Unnecessary use or excessive use of the antibiotic can reduce its effectiveness and can cause side effects. Overuse may result in oral thrush, or it may lead to the development of a new vaginal yeast infection.

Metronidazole dosage, and the duration of treatment may vary according to age of the patient, type of infection, and severity of the condition. If the antibiotic is not taken with food or a glass of water or milk, the patient may experience stomach upset. The side effects may vary from patient to patient depending upon the overall health of the patient. Taking the antibiotic at evenly spaced intervals help maintain the amount of medicine in the body at a constant level.

Pregnant women and nursing mothers should avoid use of this antibiotic as it can lead to adverse effects on the fetus and the infant respectively. The symptoms of the disease may go away with a few doses of metronidazole 500 mg tablets; however, you are expected to take the medication for the entire length of time as prescribed by your doctor. Otherwise, a relapse of the infection can be experienced. Similarly, you are supposed to inform your doctor if your condition worsens, if you notice any of the aforementioned side effects, or if the condition persists.

Disclaimer: This HealthHearty article is for informative purposes only, and should not be used as a replacement for expert medical advice.