Ophthalmology

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Chapter 22 Ophthalmology

Ophthalmic Prostaglandins

Description

Ophthalmic prostaglandins (PGs) are topically applied for treating glaucoma.

Prototype and Common Drugs

image Prototype: latanoprost (all are PGF2α)
image Others: travoprost, bimatoprost, unoprostone

MOA (Mechanism of Action)

image Glaucoma is characterized by increased intraocular pressure (IOP) and can lead to blindness if not treated. Strategies to reduce IOP include reducing the production and secretion of aqueous humor and facilitating its drainage.
image Drainage occurs via two main pathways

image 80% to 90% via Schlemm’s canal (the trabecular network)
image 10% to 20% via the uveoscleral route (Figure 22-1)

image PGs bind prostaglandin F (FP) receptors that are located on the ciliary muscle and reduce IOP by increasing outflow of aqueous humor through the uveoscleral pathway. This is thought to be accomplished through the following mechanisms:

image Relaxation of the ciliary muscle
image Vasodilatation as a contributor to early effects
image Remodeling or shrinking of the ciliary muscle, resulting in increased space for outflow as a mechanism for long-term control of glaucoma

image Administering exogenous PG-F (specifically PGF2α) stimulates the FP receptor and increases aqueous outflow through the mechanisms just described.
image

Figure 22-1

Pharmacokinetics

image These PGs are administered topically to the eye, and only a small amount reaches the systemic circulation.

Indication

image Glaucoma

Contraindications

image Previous cystoid macular edema is a contraindication and previous incisional surgery on the eye is a risk factor; ocular PGs should be used with caution in these patients because of the increased risk of cystoid macular edema.

Side Effects

image Local irritation: Conjunctival hyperemia (redness), itching, foreign body sensation, tearing, and eye pain are side effects.
image Blurred vision may occur.
image Pigmentation of the iris: This occurs in patients with mixed-color irises (green-brown or blue-brown) and is a result of increased deposition of melanin. Pigmentation of the palpebral skin (eyelids) also occurs.
image Eyelash growth occurs with unoprostone only.
image Cystoid macular edema involves accumulation of fluid in the macular area of the retina. This is a well-recognized complication of cataract surgery.
image Punctate epithelial keratopathy involves loss of superficial epithelial cells and associated defects on the cornea.

Important Notes

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