Comparative efficacy study of brimonidine tartrate 0.15% and timolol maleate 0.5% ophthalmic solution (benzalkonium chloride free) versus Brimolol® (with benzalkonium chloride) following single ocular instillation in New Zealand white rabbits

Amit Thavkar, Sateesh Kumar Chauhan, Subhas Bhowmick, Vinod Burade


Background: Benzalkonium chloride (BKC) is the most used preservative in topical eye drops but it causes effects such as dry eye and trabecular meshwork degeneration. Polyhexamethylene biguanide (PHMB) is a polymeric biguanide is a less harmful preservative used in ophthalmic solutions. The objective of this study to com-pare the efficacy of PHMB preserved versus BKC preserved ophthalmic solutions containing brimonidine tartrate and timolol maleate on intraocular pressure (IOP) following single ocular instillation in New Zealand white (NZW) rabbits.

Methods: This study was conducted on 12 normotensive male NZW rabbits (2.9-3.6 kg) between 6-9 months of age. Animals received single ocular instillation of 35 µl ophthalmic solution containing brimonidine tartrate 0.15 %w/v and timolol maleate 0.5% w/v with PHMB as preservative (n=6, test) or BKC as preservative (n=6, reference) as per the randomization. Intraocular pressure (IOP) was measured before and 2, 4, 6, 8 and 24 hours after instillation using a pneumatonometer. Percentage change in IOP from pre-instillation values were calculated. Changes in IOP were analysed using the repeated-measures analysis of variance followed by Bonferroni post-test.

Results: Single ocular instillation of PHMB and BKC formulations show significant IOP reduction up to 6 hours as compared with baseline (p<0.05). Reduction in IOP was 35.8% and 32.0% at 2 hours with PHMB and BKC formulations respectively. No differences were observed between the test and reference groups for change in IOP from baseline.

Conclusions: PHMB preserved brimonidine tartrate 0.15% w/v and timolol maleate 0.5% w/v ophthalmic solution was comparable to BKC preserved solution in normotensive NZW rabbits.


Polyhexamethylene biguanide, Ophthalmic solution, Intraocular pressure, Brimonidine, Timolol

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