In a breastfeeding mother with allergic conjunctivitis (red eyes and white string-like discharge) likely triggered by cat exposure, which topical antihistamine eye drops are safe to use, and is the oral antihistamine bilastine safe during lactation?

Recommended Treatment for Allergic Conjunctivitis While Breastfeeding

Use bilastine 0.6% preservative-free eye drops once daily for your allergic conjunctivitis symptoms—this is safe during breastfeeding and will effectively treat both your red eyes and the white stringy discharge (mucus strands) you're experiencing.

Eye Drop Treatment

The white strings you're seeing are mucus strands, a classic sign of allergic conjunctivitis. Bilastine 0.6% ophthalmic solution is your best option because it:

• Provides 16-hour symptom relief with once-daily dosing 1, 2
• Is preservative-free and contains sodium hyaluronate, which protects and hydrates your ocular surface 3
• Demonstrates rapid onset (works within 15 minutes) and sustained efficacy 4
• Shows minimal systemic absorption—plasma concentrations after eye drop use are extremely low (mean maximum of only 2682 pg/mL) 5

The minimal systemic absorption is critical for breastfeeding safety. When bilastine eye drops are used, the drug is primarily absorbed by the conjunctiva with negligible amounts entering your bloodstream 5, making transfer to breast milk essentially insignificant.

Oral Bilastine During Breastfeeding

Regarding oral bilastine: second-generation antihistamines are considered safe during lactation 6. A 2026 study specifically examining medication use in 515 breastfeeding women found that second-generation antihistamines (which includes bilastine) were commonly used and all prescribed medications were classified as safe or fairly safe during lactation, with relative infant doses below 10% 6.

However, prioritize the topical eye drops over oral medication since your symptoms are primarily ocular. The eye drops provide targeted relief with virtually no systemic exposure, eliminating any theoretical concerns about breast milk transfer.

Treatment Algorithm

1. First-line: Bilastine 0.6% eye drops once daily in affected eyes
2. If nasal symptoms develop: Consider adding oral bilastine (safe during breastfeeding)
3. Avoid cat exposure when possible to reduce allergen load
4. Monitor for improvement within 15 minutes of first dose; full effect sustained for 16 hours

Important Caveats

• The bilastine eye drop formulation is preservative-free, which is crucial for long-term use and reduces risk of preservative-related toxicity 7
• Do not confuse bilastine eye drops with the FDA-labeled bilastine products 8 which appear to be for lip/cold sore treatment—these are different formulations
• If symptoms persist beyond 3-4 days despite treatment, return for re-evaluation to rule out bacterial superinfection
• The mucus strands (white strings) should resolve as the allergic inflammation improves with antihistamine treatment

The evidence strongly supports bilastine 0.6% ophthalmic solution as safe, effective, and convenient for breastfeeding mothers with allergic conjunctivitis 1, 2, 4.