Metronidazole (Vaginal) (NidaGel)

1. Health Canada Product Monograph — Metronidazole (Vaginal)

• Local treatment of bacterial vaginosis in non-pregnant adults, diagnosed by a thin, grey-white discharge with a fishy odor, vaginal pH greater than 4.5, and clue cells on microscopy, or by Gram stain criteria.
• Not effective against trichomoniasis (which requires an oral, systemically-absorbed regimen) or candidiasis; confirm the diagnosis before treating.

• Metronidazole crosses the placenta and enters the fetal circulation. Vaginal metronidazole should not be used in the first trimester of pregnancy.
• There is limited experience with vaginal metronidazole specifically in later pregnancy; when treatment of bacterial vaginosis is needed for a pregnancy-related indication (such as reducing risk of preterm birth in a high-risk pregnancy), an oral metronidazole regimen is preferred over the vaginal gel.

• Systemic absorption after vaginal application is low compared with oral metronidazole, but some absorption does occur. Oral metronidazole is excreted into breast milk; if there is concern, a temporary interruption of breastfeeding can be considered, though many sources consider usual doses compatible with breastfeeding.

• No specific dosing adjustment is described for older adults.

• Not indicated for pediatric use; this is a vaginal product formulated and studied in adult women.

• Standard regimen: one applicatorful (approximately 5 g) inserted intravaginally once daily at bedtime for 5 consecutive days.
• Recurrent bacterial vaginosis (4 or more episodes per year): after completing a 10-day daily induction course, continue with 5 g intravaginally twice weekly as maintenance therapy for 4 to 6 months.
• Insert using the applicator provided; treatment can be given regardless of the timing of menses.

If overdose is suspected, seek emergency medical attention immediately or contact your regional Poison Control Centre without delay.

• No specific vaginal overdose syndrome is described given low systemic absorption; accidental oral ingestion of the tube's contents by a child should be treated as a potential exposure — contact Poison Control for guidance.

• Vulvovaginal itching, burning, or irritation.
• Vaginal discharge (a watery or gel-related discharge distinct from the original bacterial vaginosis discharge).
• A metallic taste has been reported even with vaginal use, reflecting some systemic absorption.

Serious side effects require immediate discussion with the prescriber or emergency care.

• Peripheral neuropathy (numbness, tingling in the hands or feet) has been reported rarely, more typically with prolonged systemic use, but should prompt discontinuation if it occurs.
• Severe hypersensitivity reactions, including rash and, rarely, angioedema.

• Use with caution in patients with a history of blood dyscrasias or central nervous system disease, given the (low but nonzero) systemic absorption of metronidazole with vaginal use.

• Known hypersensitivity to metronidazole, other nitroimidazole derivatives, or any component of the gel (including parabens).
• First trimester of pregnancy.

• Alcohol: a disulfiram-like reaction (flushing, headache, nausea, vomiting) is possible even with vaginal use, due to some systemic absorption — avoid alcohol during treatment and for at least 24 hours after finishing.
• Warfarin and other oral anticoagulants: metronidazole can potentiate anticoagulant effect even at the lower systemic exposure achieved vaginally; monitor INR if used concurrently.

• None specific beyond the alcohol interaction noted above.

• Insert at bedtime to reduce leakage and maximize contact time with the vaginal mucosa overnight.

• Store between 15°C and 25°C. Do not freeze.

• Complete the full course even if symptoms improve early, to reduce the risk of relapse.
• Avoid alcohol during treatment and for at least 24 hours afterward, since it can cause flushing, nausea, and vomiting even with this vaginal formulation.
• Contact your pharmacist or prescriber if you notice numbness or tingling in your hands or feet, or if symptoms do not improve.
• If pregnant or planning pregnancy, tell your prescriber — this product should not be used in the first trimester.