3.5.3 Pharmacology I
Lab 4 Effects of Pilocarpine on Rabbit's or Guineapig's Eye
Pilocarpine stimulates cholinergic receptors of sphincter muscles in the iris and thus exerts miotic action on eye. Also produces vasodilation of conjunctival vessels of the out flow tract and contraction of ciliary muscles, resulting in accommodation with deepening of the anterior chamber.
Available forms of Pilocarpine
Pilocarpine hydrochloride (gel 4%, solution 0.25%-10% w/v, & tablet 5 mg.) and Pilocarpine nitrate (solution 1%, 2% & 4% w/v).
Pilocarpine nitrate, therapeutically used in chronic open angle glaucoma (dose: 1-2 drops of 1-4% w/v solution installed in lower conjunctival sac every 4-12 hrs), emergency treatment of
acute narrow angle glaucoma (1 drop of 2% w/v solution every 5 minutes for 3-6 doses & then 1 drop for 3 hrs) and to counteract mydriatic effects of sympathomimetics (1 drop of 1% w/v solution in affected eye).
Onset of action
Onset of action of the ophthalmic preparation is 10-30 minutes and duration of action is 4-8 hrs.
Over dose of Pilocarpine nitrate causes myopia ('nearsightness', due to complete relaxation of ciliary muscle), conjunctival irritation.
The parameters (pupillary diameter, lighting reflex and conjunctival reflex) of Rabbit's eye are measured without the installaton of drug followed by the installation of Pilocarpine nitrate in either left or right eye of the Rabbit. Again the above parameters are measured in every 10 minutes gap, until these come into normal range.
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