Bacterial Vaginosis

Bacterial vaginosis (BV) results from a shift in the normal vaginal flora: the lactobacilli that normally dominate are replaced by an overgrowth of anaerobic organisms, chiefly Gardnerella vaginalis along with Mycoplasma species and other anaerobes. BV is not itself classified as a sexually transmitted infection, and — unlike trichomoniasis — male sexual partners are not treated, since partner treatment does not reduce recurrence. Treatment is reserved for symptomatic patients and a specific set of asymptomatic situations where treatment is protective.^[1]

• New or multiple sexual partners, and a new sexual relationship generally — though BV is not classified as an STI itself.
• Vaginal douching.
• Absence of condom use (some association, though causality is less clear-cut than for classic STIs).
• Lack of vaginal lactobacilli for any reason, including recent antibiotic use.
• Recurrence is common, and a clear single cause for recurrent BV is often not identifiable.

Differentiating the 3 vaginal discharge infections

Nonsexually transmitted causes of vaginitis are also common and include atrophic vaginitis, trauma, contact or irritant dermatitis (detergents, contraceptive chemicals), foreign bodies, and allergy (e.g., latex condoms). Candidiasis and bacterial vaginosis are not generally considered sexually transmitted; trichomoniasis is.

Simple bedside diagnosis

• Vaginal pH over 4.5 — check with pH paper; a normal pH under 4.5 argues against BV.
• Positive "whiff" test — a fishy odour on mixing a sample with 10% potassium hydroxide (KOH).
• Clue cells on microscopy — vaginal epithelial cells covered with numerous coccobacilli, seen on a saline wet mount.

Amsel's clinical criteria (discharge appearance, pH over 4.5, positive whiff test, and clue cells — 3 of 4 required) or a Gram-stain-based scoring method are both acceptable diagnostic approaches; use whichever your setting supports. NAAT-based testing is increasingly available and can support the diagnosis in more equivocal cases.^[1]

• Resolve discharge, odour, and any associated discomfort in symptomatic patients.
• Prevent BV-related complications before IUD insertion, gynecologic surgery, therapeutic abortion, or upper genital tract instrumentation.
• Reduce the risk of preterm birth in pregnant patients at high risk who are also symptomatic or otherwise meet treatment criteria.

• Reduce or avoid vaginal douching, which disrupts normal flora.
• Consistent condom use may modestly reduce recurrence risk, although evidence for this is not as strong as for classic STIs.
• No partner treatment or partner notification is indicated.

Breastfeeding: it is not necessary to withhold breastfeeding during metronidazole treatment; some clinicians advise against breastfeeding for 12–24 hours specifically after a 2 g single dose.

• Retest 1 month after completing oral metronidazole therapy to confirm treatment success — recurrence within the first few months of treatment is common enough that this follow-up is worthwhile.
• Reassess promptly if odour or discharge returns before 1 month, rather than waiting for the scheduled follow-up.
• For recurrent BV, look for and address contributing factors, and consider extended or maintenance therapy (see Drug Tables).

1. Confirm the regimen was completed correctly, including full duration for topical therapy.
2. Re-examine and retest to confirm the diagnosis is still BV and not a different or superimposed cause of discharge.
3. For a single recurrence, retreat with the same or an alternative first-line regimen.
4. For recurrent BV (3 or more episodes per year), move to an extended-duration or maintenance regimen (see Drug Tables) and address contributing factors such as douching.
5. Refer for gynecologic assessment if recurrence continues despite an adequate extended regimen.

• Treating asymptomatic BV outside the specific indicated situations (pre-procedure, high-risk pregnancy).
• Treating the male sexual partner — this is not indicated and does not reduce recurrence.
• Using topical therapy in a high-risk pregnant patient when the goal is preventing preterm birth — use a systemic regimen instead.
• Attributing persistent pruritus or inflammation to BV — these findings point toward candidiasis or trichomoniasis instead.

How to use this table: Doses are adult doses and require patient-specific confirmation, including renal/hepatic adjustment. Male partners are not treated. Select any drug name to open its complete Pharmasist Drug Database page.

Nitroimidazoles

Both oral and topical metronidazole are preferred first-line options.

Lincosamides

Preferred topical alternative to metronidazole; oral clindamycin is a systemic alternative.

Evidence note: Drug inventory, dosing, adverse effects, and comments reflect standard Canadian practice per current PHAC guidance.^[1]