Using Prostaglandins for Contemporary Therapy
BY LEO SEMES, OD, FAAO
Topical beta-blockers have been the gold standard for lowering intraocular pressure (IOP) for a quarter of a century. When they were first introduced, they replaced the burdensome and uncomfortable cholinergic and adrenergic regimens.
Within a year, reports cited corneal anesthesia as a side effect, cardiopulmonary side effects and even death. Today, practitioners prescribing topical beta-blockers must monitor systemic medications so they don't topically duplicate a benefit that a systemic beta blocker may provide.
The new age of glaucoma treatment dawned with the introduction of latanoprost 0.005% (Xalatan, Pharmacia) in the class of drugs widely called prostaglan-dins. They're naturally occurring fatty acids (lipids) found throughout the body, and they produce a variety of biological effects.
The four commercially-available prostaglandin analogues that lower IOP are unoprostone isopropyl (Rescula, Novartis Ophthalmics), travaprost (Travatan, Alcon), bimataprost (Lumigan, Allergan) and latanoprost.
Physicians have written over 50 million prescriptions for latanoprost alone. Other prostaglan-dins make up additional market share for these ocular hypotensive lipids that have become the most frequently prescribed glaucoma agents in the United States.
A Look at Latanoprost
It's believed that increased uveo-scleral outflow decreases IOP. Once inside the eye, latanoprost is hydrolyzed to the acid form where it binds to FP receptors in the ciliary body and begins the degradation of collagens that results in reduced resistance and increased outflow.
Latanoprost reduces IOP 24 to 33 percent with once daily dosing. It's been shown to be more effective than a combination of timolol and pilocarpine and at least as effective as timolol plus dorzolamide. More recent studies indicate efficacy as monotherapy.
The most frequently encountered side effect with latanoprost is conjunctival hyperemia. Along with burning and stinging at instillation, this is generally mild and occurs in fewer than 15 percent of patients. Latanoprost is contraindicated in cases of previous iritis/uveitis. Also consider patients who've suffered CME as poor candidates for this therapy.
The most visible side effects are iris color change and hypertrichosis (Figure 1a and b), so tell patients who are at the greatest risk (those with blue or brown irides) about this. A herpes-like pseudodentrite epithelial defect involving the cornea and eyelid skin may be treated palliatively.
Figure 1a. Iris darkening with latanaprost. Before (left) and after six months (right).
Figure 1b. Hypertrichosis following latanaprost therapy. Before (left) and after (right).
When NSAIDs and Prostaglandins Mix
You may expect that systemic nonsteroidal anti-inflammatory drug (NSAID) therapy might counteract the ocular hypotensive effect of prosta-glandins. But a recent report suggested that systemic administration of indomethacin (25 mg qid) negated the ocular hypotensive effect of brimonidine but not latanoprost. This study reminds us that we should check the systemic medications and health conditions of our patients.
Dr. Semes is an associate professor at the University of Alabama at Birmingham School of Optometry.