Metronidazole for Bacterial Vaginosis
Metronidazole is classified as a nitroimidazole antiprotozoal and antibacterial agent used to treat protozoal infections and anaerobic bacterial infections, including1:
The most common side effects are gastrointestinal, particularly nausea reported by about 12% of patients, headache, vomiting, diarrhea, metallic taste, and abdominal discomfort.
Efficacy for Bacterial vaginosis
Bacterial Vaginosis (non-specific vaginitis or Gardnerella vaginitis) is the most common cause of abnormal vaginal discharge, characterized by vaginal malodor and increased white discharge. BV results from the replacement of the normal vaginal flora (Lactobacillus spp.) with a mixture of potentially pathogenic bacteria, including Gardnerella, Mobiluncus, Mycoplasma hominis, Prevotella, and Atopobium vaginae.
BV is often associated with pelvic inflammatory disease and can also lead to anaerobic bacterial infection of the endometrium and salpinge. Bacterial vaginosis early in pregnancy significantly increases the risk of preterm delivery. Bacterial present in BV may produce substances that favor survival of Chlamydia trachomatis.
Metronidazole is the preferred antibiotic for the treatment of BV. The cure rate ranges from 75 to 84 percent4. However, Atopobium vaginae is resistant to metronidazole, and is associated with recurrent bacterial vaginosis after treatment with metronidazole.
Oral metronidazole eradicates BV-associated bacteria better than vaginal formulation3. However, metronidazole vaginal gel is a reasonable choice for women experiencing side effects of oral metronidazole2.
Recurrent Bacterial Vaginosis
Dosage for Bacterial vaginosis
Oral: 500 mg twice daily for seven days.
Vaginal: Metronidazole vaginal gel (0.75%) twice daily for 5 days. One full applicator (approximately 37.5 mg metronidazole) is applied intravaginally in the morning and in the evening. Treatment with metronidazole gel is moderately effective for bacterial vaginosis.
Recurrent BV: In case of more than three episodes of bacterial vaginosis during past 12 months vaginal metronidazole gel may be used to prevent relapses. The regimen is twice weekly for 4-6 months7-8.
Regimens for pregnant women: Metronidazole is an acceptable therapy for BV during pregnancy8. However, some clinicians are hesitant to prescribe metronidazole in pregnant women because there are not enough studies confirming its safety. According to CDC Guidelines8 Clindamycin (300 mg twice a day for 7 days) is an alternative to metronidazole for the treatment of BV.
Mechanism of action
Metronidazole is an anti-pathogen with selective toxicity to microaerophilic, anaerobic, and anoxic or hypoxic cells. It enters bacterial or protozoal cell and inhibits DNA synthesis, resulting in cell death.
However the mechanisms by which topical preparation works in reducing inflammatory lesions of rosacea are unknown. Possible mechanisms of action include antibacterial and/or anti-inflammatory effects.
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