Probiotics in the Management of Vulvovaginal Candidosis

Vulvovaginal candidosis (VVC) represents a frequent and cumbersome vaginal infection. Recurrent and/or persistent infections remain common among a significant number of patients despite the use of antifungals. Probiotics offer a promising adjunctive or alternative therapeutic strategy to antifungals in the management of VVC. We aimed to explore and thoroughly examine the various roles and potential applications of probiotics in VVC. A comprehensive literature search was conducted to identify relevant clinical trials and systematic reviews that examine the effectiveness of probiotics in the treatment and prevention of VVC and recurrent VVC (rVVC). Following the initial screening of 4563 articles, a total of 25 clinical studies and seven systematic reviews were finally included in this analysis. The studies reviewed provide a generally positive yet inconsistent view of the efficacy of probiotics in managing VVC, including clinical, mycological response, and prevention perspectives. Nonetheless, fluconazole remains more effective than probiotics in treating VVC, while the combination of the two seems to reduce recurrence and improve symptoms significantly. For prevention, probiotics seem to improve vaginal health and reduce symptoms, while safety and tolerability are consistently reported across the studies, affirming that probiotics represent a low-risk intervention. However, clear conclusions are difficult to establish since relative studies explore different clinical endpoints and follow-up times, variable populations are included, different probiotics are used, and diverse schedules and regimens are administered. We propose that future studies should study the benefit of probiotics in well-defined categories such as (1) treatment with acute probiotics instead of antifungals, (2) adjuvant probiotic therapy together or after antifungals, and (3) VVC recurrence prevention using probiotics.


Introduction
The concept of using probiotics, defined as «live microorganisms that confer health benefits when consumed in adequate amounts», dates back over a century to the pioneering work of Elie Metchnikoff [1].Originally focused on improving gastrointestinal health, probiotics have since been explored for their potential benefits in various conditions in both children and adults, e.g., from colic in babies to cardiovascular disease, respiratory infection, and cancer in adults [2].Various probiotic strains exhibit distinct functions, and specific health benefits for humans have primarily been validated for particular probiotic strains.Probiotics encompass a range of genera, such as Lactobacillus, Bifidobacterium, Bacillus, Pediococcus, and various yeasts [2].Lactobacilli strains [3], in particular, have been thoroughly investigated for their ability to restore and maintain a healthy vaginal microbiome in terms of vaginal pH and bacterial colonization [4,5].Probiotics designed for vaginal health are readily available in the form of dietary supplements or vaginal capsules/suppositories [6].When applied vaginally, probiotics act directly at the site of action [7].In contrast, orally administered probiotics must pass through the gastrointestinal tract before reaching the vaginal tract [8].Interestingly, research indicates that both routes of administration are effective [9,10].Oral probiotics, however, may offer additional benefits to vaginal health through the "gut-vagina axis" [8,11].This involves balancing the gut microbiota [12,13], inhibiting or preventing the migration of urogenital pathogens from the rectum to the vaginal tract [14], and stimulating both gut and systemic immune responses [11,[15][16][17].
Their role in the management of bacterial vaginosis (BV) has long been explored [18].Administered either orally or intravaginally, the proposed mechanisms of action when it comes to BV treatment include competitive exclusion, competition for adhesion sites, production of antimicrobial substances, and modulation of the host immune response [8,19].A recent meta-analysis of available randomized controlled trials has shown that the cure rate for treating BV with a combination of probiotics and antibiotics was superior to using antibiotics alone [20].Remarkably, there was no difference in efficacy between probiotics alone and antibiotics alone, while probiotics alone were more effective than a placebo in treating BV [20].Oral probiotics seemed to be more effective than vaginal administration, and more specifically, oral administration of L. rhamnosus [20].However, one should bear in mind that the effectiveness of probiotic products relies on the number of live cells administered each time.In this context, the ideal probiotic dose remains undefined [21].It seems that high-dose probiotics were more effective than low-dose probiotics in the management of BV [20].However, the length of effectiveness varies [20].A 2019 metaanalysis revealed that probiotics alone were more effective in treating BV in both the short and long term [10].However, using probiotics after antibiotic treatment was only effective in the short term.The effectiveness varied in short-term follow-up but not in long-term follow-up.Similarly, their role in the prevention of recurrent cases of bacterial vaginosis has also been recently explored and their place is supported in select patients, either with concurrent administration or following antibiotics [5].
The potential role of such probiotics in vulvovaginal candidosis (VVC) remains an open question.VVC represents a common vaginal infection caused by an overgrowth of Candida species, primarily Candida albicans, but Candida glabrata, Candida krusei, and other species can also cause symptoms.It manifests with symptoms such as vulvar itching, burning, vulvar redness, excoriation, painful intercourse, and abnormal vaginal discharge, significantly impacting a woman's quality of life and sexual health.Typically, the initial treatment for acute VVC involves the use of topical or oral azoles [22].Recurrent and severe cases often require the administration of fluconazole, either as a repetitive single administration or as part of an ongoing suppressive therapy [23,24].Nevertheless, recurrent and/or persistent infections remain common among a significant number of patients [25].Additionally, the use of azoles disrupts the normal vaginal flora [26], particularly affecting beneficial fungi such as Saccharomyces species, which can play a role in preventing VVC [23,27].
While antifungal medications represent the standard treatment approach, there has been growing interest in exploring alternative and complementary therapies, including probiotics, to address VVC and restore a healthy vaginal microbiome [8].Firstly, certain probiotics produce enzymes that degrade the biofilm matrix or directly block Candida adhesion sites, thereby preventing initial colonization [28].Secondly, probiotics compete with Candida for both adhesion sites on the vaginal epithelium and essential growth nutrients, thereby limiting the resources available to the pathogen [8].Thirdly, probiotics such as Lactobacillus spp.secrete antimicrobial substances, including lactic acid, hydrogen peroxide, and bacteriocins, which directly inhibit both the growth and biofilm formation of Candida [29].Finally, probiotics can modulate the immune response by enhancing the activity of macrophages and dendritic cells and by regulating the balance of proinflammatory and anti-inflammatory cytokines, which improves the immunological control over Candida proliferation [30].
However, the evidence supporting the efficacy of commercially available probiotics in treating or preventing VVC remains inconclusive and is plagued by significant limitations [31].While several studies have reported promising results in terms of improved VVC cure and reduced recurrence rates, these findings are often limited by methodological flaws, such as small sample sizes, the lack of rigorous study designs, and a high risk of bias.It is noteworthy that the majority of the studies evaluated in the systematic review by van de Wijgert and Verwijs [31] were considered to have a high overall risk of bias, with only one randomized controlled trial showing a medium risk [31,32].This latter trial found no significant difference in VVC incidence between probiotic and placebo users, urging the authors to call for more robust evidence to establish the true efficacy of probiotics in VVC management [32].Prebiotics, such as oligosaccharides and polysaccharides, have also garnered interest as potential alternatives or adjuncts to probiotics in the management of vaginal infections, including VVC [33].These compounds aim to selectively stimulate the growth of beneficial lactobacilli while inhibiting the proliferation of pathogens, such as Candida species.However, the evidence in the area of yeast infections is even more limited than with bacterial infections in the vagina, with only a few clinical studies evaluating the efficacy of prebiotics in VVC management.
To comprehensively address the complexity of the subject, this review aims to explore the various roles and potential applications of probiotics in VVC.An extensive literature review has been conducted, adopting a rigorous methodology akin to that used in systematic reviews.From this review, data pertinent to the impact of probiotics on VVC have been meticulously extracted and systematically organized into three categories: the first concerns the treatment of VVC with probiotics; the second focuses on the preventive applications of probiotics, while the third compiles all evidence available from the systematic reviews pertaining to the use of probiotics in managing VVC.This structured approach aims to provide a clear and comprehensive synthesis of the current evidence, identifying both the potential benefits and limitations of probiotics in VVC management, thereby informing future research directions and clinical practices.

Study Selection and Data Extraction
Four independent reviewers performed a literature search and identified articles, which were then hand-searched for relative references.Articles were included if they were clinical studies or systematic reviews that reported on the effectiveness of probiotics in treating or preventing VVC or rVVC.Studies that reported outcomes related to bacterial vaginosis were also included if they contained relevant data on VVC outcomes or men-tioned VVC as an adverse event.Additionally, the relevant literature was identified through the targeted screening of references and related articles on PubMed.Non-English publications, non-human studies, and non-systematic reviews were excluded from consideration.Disagreements were discussed and resolved.
The selection process was visualized using a PRISMA flowchart (Figure 1), which delineated the stages of article elimination and selection.Data were systematically extracted and categorized into four tables: (1) clinical trials concerning the treatment of VVC/rVVC (Table 1), (2) clinical trials concerning the prevention of VVC/rVVC (Table 2), (3) clinical trials investigating the effectiveness in special populations (Table 3), and (4) systematic reviews focusing on VVC-specific outcomes following probiotic administration (Table 4).
vaginosis were also included if they contained relevant data on VVC outcomes or mentioned VVC as an adverse event.Additionally, the relevant literature was identified through the targeted screening of references and related articles on PubMed.Non-English publications, non-human studies, and non-systematic reviews were excluded from consideration.Disagreements were discussed and resolved.
The selection process was visualized using a PRISMA flowchart (Figure 1), which delineated the stages of article elimination and selection.Data were systematically extracted and categorized into four tables: (1) clinical trials concerning the treatment of VVC/rVVC (Table 1), (2) clinical trials concerning the prevention of VVC/rVVC (Table 2), (3) clinical trials investigating the effectiveness in special populations (Table 3), and (4) systematic reviews focusing on VVC-specific outcomes following probiotic administration (Table 4).

Data Synthesis
Data from the included studies were synthesized narratively.The synthesis focused on the diversity of probiotic strains used, dosages, treatment durations, and patient populations.Efficacy outcomes, including rates of symptom resolution, recurrence prevention, and incidence of adverse events, were synthesized.Considering the heterogeneity of the identified studies, the narrative synthesis allows for a comprehensive understanding of the variability and efficacy of probiotic interventions across different study designs and population subsets, facilitating an in-depth investigation of their therapeutic potential and limitations.

Data Synthesis
Data from the included studies were synthesized narratively.The synthesis focused on the diversity of probiotic strains used, dosages, treatment durations, and patient populations.Efficacy outcomes, including rates of symptom resolution, recurrence prevention, and incidence of adverse events, were synthesized.Considering the heterogeneity of the identified studies, the narrative synthesis allows for a comprehensive understanding of the variability and efficacy of probiotic interventions across different study designs and population subsets, facilitating an in-depth investigation of their therapeutic potential and limitations.
Probiotics were studied as an adjunct therapy for VVC, examining the synergy with azoles in five studies (n = 5) [39,41,43,45,49].Combined probiotic and antifungal treatments showed higher cure rates and lower recurrence rates compared to antifungal treatment alone in several studies.Probiotics enhanced the efficacy of antifungal treatments in reducing symptoms and restoring vaginal flora [39,49].Significant improvements in patient satisfaction were observed with combined treatments [49].
Systematic reviews on the efficacy of probiotics in treating VVC or rVVC have shown that probiotics with antifungal drugs improve short-term cure rates, resulting in a reduction in relapse rates within one month and showing cure rates between 57-100% [31,[59][60][61][62][63][64].However, mixed results on long-term cures were found, even though good tolerability and safety was reported across all studies.Of note, a high risk of bias was recorded in all studies, while in two, no quality assessment was reported [59,63].

Discussion
VVC is a well-characterized mucosal infection that presents a significant clinical challenge primarily due to its recurrent nature and the pathogenic resilience of Candida species.Probiotics offer a promising adjunctive or alternative therapeutic strategy to antifungals in the management of VVC [33].These beneficial microorganisms can be administered either orally or intravaginally.Oral administration facilitates colonization of the intestine, potentially influencing the vaginal flora via the gut-vaginal axis.Conversely, intravaginal delivery targets the site of infection directly, aiming at immediate colonization and action against Candida species.Similar to their use in BV [5], identification of proper population and timing remains the key to best utilizing their potential in women with acute or recurrent episodes.

Primary Treatment
Studies have shown variable results in the effectiveness of probiotics in the management of acute VVC infections [23,35,37,[40][41][42]47,49].Their use has beneficial effects in alleviating acute symptoms, including significant reduction of discharge and itching, enhancing patient comfort and quality of life [40].In this context, Vahedpoor Z et al. [45] observed improvements in itching, discharge, and vaginal pH, suggesting that probiotics might help stabilize the vaginal environment and reduce inflammation.This comes in line with data demonstrating that probiotic vaginal administration could significantly increase Lactobacillus counts in vaginal samples [50].We have recently shown that a vaginal probiotic gel with L. plantarum YUN-V2.0,L. pentosus YUN-V1.0, and L. rhamnosus YUN-S1.0 for 10 consecutive days showed a cure rate of 45%, which is below the expectations of a standard first-line treatment but still indicates that half of the patients were comfortable with the cream only, without the use of antifungals [37].The systematic reviews and meta-analyses reviewed here provide a generally positive yet inconsistent view of the efficacy of probiotics in managing VVC [31,[59][60][61][62][63][64].While short-term benefits are frequently reported, the long-term efficacy remains mostly uncertain, as most of the pooled evidence shows sparse data regarding long-term clinical and mycological cure rates.However, probiotics can by no means substitute antifungal treatment in terms of quickly reducing the fungal load.The study by Mollazadeh-Narestan et al. [42] highlighted that, while probiotics showed some benefit, fluconazole had a significantly higher frequency of negative culture results after 60-65 days, suggesting that while probiotics may be useful in managing symptoms, they might not be as effective as conventional antifungal treatments in eradicating the yeast [42].In contrast, Bertarello et al. [35] indicated that probiotics could achieve similar efficacy to standard treatments such as miconazole and provide significant symptom relief, suggesting a potential role for probiotics in managing VVC, particularly in terms of improving patient comfort and reducing symptoms such as discharge and itching.

Recurrence Prevention
When a cure does occur, maintenance therapy with probiotics could significantly reduce recurrence rates [55] and improve long-term clinical cure rates, highlighting the potential of probiotics in the ongoing management of rVVC [23,24,44].Nonetheless, the identified studies demonstrate a diverse approach to probiotic applications, both in terms of the probiotic strains used and the formulations administered.Moreover, they vary in the specific outcomes measured, which presents significant challenges in judging the potential role of probiotics in preventing VVC [23,36,38,39,41,46,49].For instance, the RCT by Pirotta et al. [56], which is the most powerful in this review, with 278 participants and a robust 2 × 2 factorial design, is particularly noteworthy in that it employed both an oral and a vaginal route of administration.It did not demonstrate a significant difference in the prevention of post-antibiotic vulvovaginitis between the probiotic and placebo groups.On the other hand, the multicenter RCT by Vladareanu et al. [58], which included 93 Caucasian women with a history of recurrent yeast vaginitis, observed significant improvements in vaginal health scores and reductions in symptoms such as vaginal mucosa redness and swelling following treatment with L. plantarum P17630.Similarly, in order to prevent recurrences, a 2014 observational study by Murina et al. [54] from Italy reported impressive results regarding the synergistic potential of combining vaginal probiotics with fluconazole to reduce recurrence rates.This study assessed a slow-release vaginal product containing Lactobacillus strains, following induction treatment with oral fluconazole, in 58 patients with acute symptomatic VVC who also had a history of rVVC, with four or more culture-confirmed episodes in a 12-month period.The investigated regimen reportedly resulted in 86.0% of the participants remaining free of clinical recurrence during the 10-week prophylactic phase and 85.7% remaining symptom-free over the subsequent 7-month observation period.Given the recurrent nature of VVC, more focus should be placed on investigating the efficacy of probiotics over more extended periods to fully understand their role in preventing relapses and sustaining vaginal health.Another limitation is the insufficient evidence regarding the ability of administered probiotic strains to effectively colonize the vagina.Successful colonization is critical for the prolonged efficacy of probiotics in modifying the vaginal microbiota and exerting their beneficial effects [65].Without this sustained presence, the transient existence of probiotics may be inadequate to influence the underlying pathophysiology of VVC, particularly regarding long-term outcomes.Furthermore, the substantial heterogeneity among the included studies, as highlighted in several meta-analyses, complicates the aggregation of data and the interpretation of outcomes.

Adjuvant Therapy
Finally, the synergy between probiotics and antifungals may enhance the overall treatment efficacy.For instance, Martinez RC et al. [41] observed that the combination of fluconazole with probiotics resulted in higher cure rates of VVC compared to fluconazole alone (adjuvant probiotic therapy).Similarly, Pendharkar S et al. [43] demonstrated that adjunctive use of EcoVag ® with fluconazole not only achieved high cure rates at 6 months but also maintained these effects for up to 12 months, indicating sustained benefits when probiotics are used with antifungals.

Safety
Although relatively safe, there is always the potential risk that probiotics, as living organisms, could cause infections that require antibiotic treatment, particularly in individuals with underlying health conditions.Many probiotic strains are genetically modified in laboratories to enhance their health benefits.Therefore, the safety of each strain must be ensured and closely monitored to prevent environmental accumulation, possession of antibiotic selection markers, or transfer of harmful genetic information to other bacteria [2].Safety and tolerability are consistently reported across the studies, including in our report, affirming that probiotics represent a low-risk intervention [52].The absence of serious adverse effects and the general improvement in vaginal health parameters point to the potential benefits of probiotics in the management of VVC [53].However, their overall effectiveness can be highly context-dependent, influenced by factors such as the probiotic strains used and possibly the route of administration.Despite promising results, the evidence remains fragmented due to methodological diversity and small sample sizes in many of the studies.The observational and retrospective studies, such as those by Reid et al. [57] and De Seta et al. [51], while providing valuable preliminary data, contribute low-quality evidence due to their inherent design limitations.Nonetheless, these studies support the safety and tolerability of probiotics, noting improvements in patient-reported outcomes and reductions in infection recurrence rates.

Cost-Effect Considerations
Despite the lack of robust clinical evidence, the demand for pro-/pre-biotic approaches to enhance vaginal health continues to grow, fueled by consumer interest and a multi-billion-USD global market.Probiotic cost-effectiveness has been demonstrated in the context of hospitalized adult patients receiving antibiotics, as well as the prevention of Clostridium difficile-associated diarrhea in children and adolescents [66,67].In this case, probiotics have been found to be economically attractive across a wide range of plausible values, but not in all scenarios [66][67][68].This was not the case though for the prevention of ventilatorassociated pneumonia, where probiotics were found not to be cost-effective across wide ranges of plausible willingness-to-pay thresholds [69].A paucity of cost-effectiveness data exists regarding its use in bacterial or fungal vaginosis, which, considering the lack of significant benefit despite their relative safety, does not support their use as standardof-care in the management of VVC.Special focus should be put on how host factors, such as age, hormonal status (e.g., menopause), immune status, and underlying medical conditions (e.g., diabetes and HIV/AIDS), influence the effectiveness of probiotics in managing VVC.Understanding these factors can help tailor probiotic therapies to specific patient populations and optimize treatment outcomes and cost-effectiveness.This aspect could provide valuable insights into the personalized use of probiotics in clinical practice, addressing the variability in treatment response among individuals with different health profiles and resulting in patient risk stratification models that could maximize benefitrisk/cost ratios.

Conclusions
The diversity in study designs, outcome measures, and variations in probiotic formulations pose the main challenges in drawing definitive conclusions.The high risk of bias and overall low quality of evidence observed in many studies necessitate cautious interpretation of these results.As regulations surrounding probiotic product claims tighten [70], there is an urgent need for studies investigating standardized and well-defined probiotic products.High-quality, well-designed randomized controlled trials are then needed to establish the true efficacy and appropriate use of pro-/pre-biotics in the management of VVC, including well-defined endpoints, and investigations into the optimal duration, route, and timing of probiotic administration for maximum efficacy.We propose that future studies should study the benefit of probiotics in well-defined categories such as (1) acute probiotics treatment instead of antifungals, (2) adjuvant probiotic therapy together or after antifungals, and (3) VVC recurrence prevention using probiotics.Such research efforts are crucial to providing patients and healthcare providers with the evidence needed to make informed decisions about the potential benefits and limitations of incorporating pro-/pre-biotics into the clinical management of VVC, either as a standalone therapy/prophylaxis or as an adjunct to traditional antifungal treatments.

Figure 1 .
Figure 1.The selection process is visualized using a PRISMA flowchart, which delineates the stages of article elimination and selection.

Figure 1 .
Figure 1.The selection process is visualized using a PRISMA flowchart, which delineates the stages of article elimination and selection.

Table 1 .
Clinical Trials investigating the effectiveness of probiotics in treating VVC and/or rVVC.
[40]severe or non-serious adverse events were reported in both groups.Mändar R et al.[40]2023 Estonia Randomized double-blind placebo-controlled two-arm parallel trial.182 women recruited with vaginitis-89 BV and 93 VVC (aged 18-50 years) Probiotic capsules (either oral or vaginal probiotic capsules, administered over three months) containing L. crispatus strains-DSM32720, DSM32718, and DSM32716, in case of VVC-.(3 × 10 10 CFU/capsule).Capsules containing maltodextrin -Clinical Improvements in VVC: Symptom Relief: Both (oral or vaginal) probiotic groups experienced significant reductions in the amount of discharge and itching.Vaginal Probiotic Group: significant relief from itching (p = 0.035) and discharge (p = 0.047) Oral Probiotic Group: Statistically significant reduction in discharge (p = 0.050) -Microbial Analysis: Lactobacilli Increase: statistically significant increase in Lactobacillus counts in the vaginal samples from the vaginal probiotic group post-treatment (p = 0.028).Other Microorganisms: G. vaginalis Counts: Decreases were more pronounced in the oral probiotic group, although not statistically significant (p = 0.114).

Table 2 .
Clinical Trials investigating the effectiveness of probiotics in preventing Vulvovaginal Candidiasis (VVC) and/or Recurrent-VVC.

Table 3 .
Clinical Trials investigating the effectiveness of probiotics in treating and preventing VVC in special populations.

Table 4 .
Systematic Reviews reporting on VVC-specific outcomes following probiotic administration.