The use of small volume ocular sprays to improve the bioavailability of topically applied ophthalmic drugs

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It is accepted that the standard eyedrop volume of 25–50 μl is too large to be accommodated within the conjunctival sac, leading to overspill and to rapid drainage into the nasolacrimal duct. This drainage can lead to unwanted systemic absorption of the active agent, which could be avoided if the dropsize were smaller. In this study, we have evaluated the efficiency of small volume ocular sprays in achieving target corneal drug concentrations. A five-way cross-over pharmacodynamic study was initiated using 10 New Zealand white rabbits as the test subjects. The efficacy of a 30 μl instillate of a 1% w/v pilocarpine hydrochloride solution was compared to 5 μl ocular sprays of 1, 2, 3 and 4% w/v solutions. The efficacy of these treatments was determined by measuring the pupillary miotic responses of the rabbits using video imaging. Analysis of the miotic response showed no significant differences between the treatments, e.g. the area under the miosis-time curve for a 30 μl drop of a 1% pilocarpine hydrochloride solution was 3871 c.f 3827 for a 1% spray despite a six-fold reduction in the administered volume and drug loading. This study demonstrates that the spray delivery of 5 μl volumes of pilocarpine hydrochloride, at concentrations of 1, 2, 3 and 4% achieved an equivalent miotic response to that of a 30 μl volume instillate of a 1% solution.