After an eye examination, a male client is diagnosed with open-angle glaucoma. The physician prescribes Pilocarpine ophthalmic solution (Pilocar), 0.25% gtt i, OU q.i.D. Based on this prescription, the nurse should teach the client or a family member to administer the drug by:
A. Instilling one drop of pilocarpine 0.25% into both eyes daily.
B. Instilling one drop of pilocarpine 0.25% into both eyes four times daily.
C. Instilling one drop of pilocarpine 0.25% into the right eye daily.
D. Instilling one drop of pilocarpine 0.25% into the left eye four times daily.
Correct Answer: B. Instilling one drop of pilocarpine 0.25% into both eyes four times daily.
The abbreviation “gtt” stands for drop, “i” is the apothecary symbol for the number 1, OU signifies both eyes, and “q.i.d.” means four times a day. Therefore, one drop of pilocarpine 0.25% should be instilled into both eyes four times daily. Pilocarpine is a muscarinic acetylcholine agonist that is effective in the treatment and management of acute angle-closure glaucoma and radiation-induced xerostomia. Although not a first-line treatment for glaucoma, it is useful as an adjunct medication in the form of ophthalmic drops.
Option A: Pilocarpine is approved for use as an agent to decrease IOP in cases of glaucoma, as well as in the management of xerostomia resulting from radiation exposure and Sjogren disease. Its mechanism of action includes both full and partial agonism of the muscarinic M3 receptor, which is an acetylcholine receptor. It is important to note that pilocarpine may have effects on the M1-M3 receptor subtypes, which causes parasympathetic side effects later discussed in this paper. The M3 receptor is an excitatory receptor expressed in gastric glands, salivary glands, and smooth muscle cells, such as those present in the pupillary sphincter and ciliary bodies.
Option C: By stimulating the Gq receptor, the M3 receptor can activate phospholipase C. This leads to the creation of the second messenger’s inositol trisphosphate and diacylglycerol, as well as calcium and protein kinase. M3 cholinergic agonists, therefore, result in the upregulation of calcium, and ultimately smooth muscle contraction such as in the pupillary sphincter muscle.
Option D: When used as a miotic agent, pilocarpine is available in the form of ophthalmologic eye drops. This dose form will result in ciliary contraction (a contraction of the iris), which will increase aqueous humor outflow, miosis, and accommodation. The ciliary body connects to the zonular fibers that control the accommodation of the lens. Contraction of the ciliary body will relax the zonular fibers, which results in a more spherical shape of the lens and therefore allowing aqueous outflow to occur. This conformational change is helpful to decrease intraocular pressure in glaucoma.
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