Olopatadine in Seasonal Allergic Conjunctivitis: Efficacy, Ocular Surface Safety, and Practical Considerations for Preservative-Free Multidose Therapy

Background: Seasonal allergic conjunctivitis (SAC) is the most prevalent form of ocular allergy, characterized by recurrent episodes of IgE-mediated conjunctival inflammation triggered by seasonal aeroallergens (pollens). Its clinical course typically spans 4–12 weeks for individual pollen taxa and may extend considerably longer in polyallergic patients. Olopatadine hydrochloride ophthalmic solution, a selective H1-receptor antagonist with mast cell-stabilizing properties, is one of the most extensively studied topical antihistamines for SAC and is highly ranked in comparative evidence networks. Two clinically relevant aspects have received insufficient attention: the impact of benzalkonium chloride (BAK), a preservative, on the conjunctival surface, and the implications of bottle size for treatment adherence during SAC’s prolonged symptomatic periods. Methods: A non-systematic narrative review of the literature was conducted. PubMed was searched through 6 October 2026 using combinations of terms addressing seasonal and allergic conjunctivitis, olopatadine, benzalkonium chloride, preservative-free formulations, ocular surface, pollen season, polyallergy/polysensitization, adherence/compliance, multidose systems, contamination, and in-use shelf life. Randomized controlled trials, comparative clinical studies, systematic reviews, meta-analyses, and clinically relevant mechanistic, toxicological, and microbiological studies were prioritized; reference lists of key articles were also screened. No formal systematic-review or PRISMA selection process was applied. Because direct comparative evidence for preservative-free versus BAK-preserved olopatadine and for bottle-size effects on adherence is lacking, evidence from related ophthalmic formulations was considered indirect and interpreted accordingly. Results: In the most recent network meta-analysis, olopatadine 0.1% was highly ranked among topical antihistamines for SAC (SUCRA 0.88) and perennial allergic conjunctivitis (PAC; SUCRA 0.85). However, this ranking should be interpreted together with pairwise comparisons and study-design heterogeneity, including CAC-based evidence in which alcaftadine has shown greater reduction of ocular itch at early post-challenge time points. Olopatadine acts primarily at the conjunctival surface, with low systemic exposure after topical administration. Current evidence does not establish that BAK-mediated enhancement of intraocular drug delivery is required; however, in conventional multidose bottles, it serves an important antimicrobial-preservative function, and any preservative-free multidose presentation must rely on validated container technology and an adequate in-use shelf life. For olopatadine 0.1% BID, a larger bottle may reduce the number of dispensing events during prolonged symptomatic periods, but a direct adherence benefit has not been demonstrated. Conclusions: Olopatadine remains an established topical treatment for SAC. Preservative-free formulations may avoid preservative-related ocular-surface exposure, but direct head-to-head evidence demonstrating superior ocular-surface outcomes for preservative-free versus BAK-preserved olopatadine is currently unavailable. Likewise, a larger bottle may be practically useful for BID regimens when its validated in-use period permits prolonged use, although bottle size alone should not be considered a proven determinant of adherence. Formulation choice should therefore integrate efficacy, dosing frequency, ocular-surface tolerability, container technology, in-use shelf life, cost, and the expected duration of allergen exposure.