Intravaginal vitamin C may increase short-term cure and prevent recurrence of bacterial vaginosis

This systematic review and meta-analysis evaluated the effectiveness of intravaginal vitamin C for the treatment and prevention of bacterial vaginosis (BV) in nonpregnant patients. The analysis included 1,107 participants across multiple studies, though the specific clinical settings and geographic locations were not reported. The population was exclusively nonpregnant individuals with BV, but details on age, ethnicity, or comorbidities were not provided. The follow-up periods for outcomes were 1-3 weeks for short-term cure and 6 months for recurrence.

The intervention was intravaginal vitamin C administered at a dose of 250 mg daily for 6 days. The comparators were a control group (receiving either placebo or no treatment) and a group treated with metronidazole. The specific formulation, timing, or brand of metronidazole used in the comparator studies was not detailed in the provided evidence.

The primary outcome was clinical or microbiologic cure or recurrence. For short-term cure at 1-3 weeks, intravaginal vitamin C showed a higher proportion of cure compared to control, with a relative risk (RR) of 1.57 (95% CI, 1.03-2.39). In absolute terms, 66% of patients in the vitamin C group achieved cure versus 42% in the control group. When compared directly to metronidazole, vitamin C was also associated with a higher cure rate, with an RR of 1.20 (95% CI, 1.03-1.41). This corresponded to cure rates of 62% with vitamin C versus 52% with metronidazole.

For the key secondary outcome of recurrence at 6 months, the analysis found a lower proportion of recurrence in the vitamin C group compared to placebo. The relative risk was 0.50 (95% CI, 0.27-0.93), with absolute recurrence rates of 16% in the vitamin C group versus 32% in the placebo group. No other secondary outcomes were reported in the provided data.

Detailed safety and tolerability findings were not reported. The evidence provided no information on adverse event rates, serious adverse events, discontinuations due to adverse effects, or general tolerability of the intravaginal vitamin C regimen. This represents a significant gap in the evidence base for considering this intervention in clinical practice.

These results suggest intravaginal vitamin C may have a role in BV management, but they must be interpreted in the context of the existing standard of care, typically centered on antibiotics like metronidazole or clindamycin. The finding of a potentially higher short-term cure rate versus metronidazole is notable but is based on very low-certainty evidence. Prior landmark studies have established the efficacy of antibiotic regimens, and this analysis does not yet provide sufficient evidence to alter that paradigm.

Key methodological limitations include the low to very low certainty of the evidence for all reported outcomes. The authors explicitly note that additional randomized trials are needed, particularly to evaluate recurrence beyond 1 month. Other potential biases common to meta-analyses, such as publication bias, heterogeneity between included studies, and variations in diagnostic criteria or outcome assessment across trials, were not detailed but could affect the results. The lack of reported safety data is a major limitation for clinical application.

The clinical implications are cautious. For nonpregnant patients with BV, particularly those seeking non-antibiotic options or who have contraindications or intolerance to standard therapies, intravaginal vitamin C may represent a potential alternative. However, given the evidence certainty, it cannot be recommended as a first-line treatment. Clinicians should interpret these findings as preliminary and should prioritize established, evidence-based antibiotic regimens while awaiting more robust data.

Several important questions remain unanswered. The optimal dosing and duration of intravaginal vitamin C therapy are unclear beyond the studied 250 mg for 6 days. The mechanism of action is not elucidated by this analysis. Crucially, the safety profile, including local irritation, effects on vaginal pH and flora, and long-term consequences, is completely unreported. Furthermore, the efficacy in specific subpopulations, such as patients with recurrent BV or those with certain comorbidities, is unknown. The comparison to other first-line antibiotics besides metronidazole was not evaluated.