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.