Effects of Hydrophilicity of Polymer Matrix on in Vitro Release Rate of Pilocarpine and on its Miotic Activity in Rabbit Eyes

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Abstract
Pilocarpine release and the time course of miotic activity was studied in albino rabbit eye. 3H-pilocarpine labelled matrices which contained pilocarpine base (14.2%), glycerine (10%) and polymers (PVP, HPC or their mixtures) were prepared by solution casting. Increasing the amount of PVP in the matrices increased the release rate and hygroscopicity of the matrices. Rod-shaped nonradioactive 3.2 mg matrices with 0.45 mg pilocarpine base were applied into the inferior fornix of the rabbits and the miotic effect was followed. Despite in vitro differences, the time course of miotic response did not vary between the polymer matrices. Compared to aqueous eye drop (25 μ1, 1.8% pilocarpine), the polymer matrix administration delayed the onset of the peak effect, but did not affect its magnitude. The biophasic availability was increased 1.2-fold compared to the eye drops. The rod shape and the small size of the matrices diminished the favourable effect of polymer matrices on drug bioavailability. Administration of pilocarpine in polymer matrices probably caused conjunctival vasodilatation and subsequent systemic rather than intraocular drug absorption.