Safety of carrageenan-based gels as preventive microbicides: a narrative review.

Background: Carrageenan-containing gels researched for the prevention of sexually transmitted infections (STIs) have shown promising results for human papillomavirus prevention in women, but not in men. We conducted a narrative review to assess the safety of these gels for genital use.

Methods: We searched PubMed using MeSH terms and keywords on 5 November 2023. Title/abstract of articles were screened to identify relevant ones. Full-text screening determined eligibility: empirical study evaluating safety of carrageenan-containing gel(s) for genital use.

Results: Of the 125 identified records, 15 were eligible, comprising 14 (10 randomised controlled trials and 4 cohorts) unique study populations. Studies included women only (n=11), men only (n=1) or both (n=3); number of participants ranged from 4 to 6202. Safety was assessed for vaginal (n=13), penile (n=3) and anal use (n=2). Most studies assessed safety of Carraguard (53%), followed by Divine9 (14%), and one each of iota-carrageenan gel, lambda-carrageenan gel, Carvir, PC-6500 (griffithsin and carrageenan) and PC-1005 (MIV-150/zinc acetate/carrageenan). Safety assessment relied on self-report (80.0%), testing for STIs (53.3%), investigator-identified genital findings (93.3%) and/or testing for changes in genital flora (60.0%). Adverse events (AEs) were described by investigators as mostly mild, (mostly) comparable between groups, not observed and/or not significant for vaginal and penile use. Only one study, assessing anal use of carrageenan, reported a significantly higher proportion of AEs in the carrageenan compared with placebo group.

Conclusions: Carrageenan-based gels are generally well tolerated for vaginal and penile, but not anal use. Studies on carrageenan gel's safety for anal use are scarce.