The agent reduces IOP to a similar degree as bimatoprost and travoprost, but latanoprost produces less irritation to the ocular surface (causing hyperemia in 5% to 15% of patients). 15,16 If latanoprost is discontinued, IOP reportedly reaches pretreatment level after 14 days. In fact, latanoprost, as well as other hypotensive lipids, is more effective when used once daily than with more frequent dosing. The sustained effect lasts for at least 24 hours, thereby allowing once-a-day administration. 13,14 Although the agent reaches peak concentration in the aqueous humor approximately 2 hours after instillation, the maximal reduction of IOP occurs between 8 and 12 hours after dosing. Latanoprost 0.005% lowers IOP by between 6 and 8 mm Hg. Latanoprost is absorbed through the cornea, where esterases hydrolyze this prodrug and change it into a biologically active acid form. The drug is highly selective for the FP type of prostanoid receptors. Latanoprost, which in 1996 became the first commercially available prostaglandin to treat glaucoma, is derived from PGF2a. 12 Diurnal IOP curves differ among various prostaglandins, but all achieve a flatter curve and better 24-hour IOP control than other groups of IOP-lowering medications. 10 PGF2a causes various ocular responses in laboratory animals, including the breakdown of the blood-aqueous barrier and subsequent IOP elevation in rabbits 11 and miosis in cats. The response to prostaglandins varies among species as well. 7 For unknown reasons, prostaglandin analogs have relatively poor corneal penetration, 8 and their efficacy was reportedly reduced in patients with thick corneas. Prostaglandins are thought to stimulate the synthesis of matrix metalloproteinases 6 that subsequently dissolve the extracellular matrix of the ciliary muscle, thus reducing IOP by enhancing uveoscleral outflow. This article describes how prostaglandins work alone and in conjunction with other drugs. 5 The development of commercially available prostaglandin analogs (hypotensive lipids) for the lowering of IOP ensued. In the early 1980s, researchers demonstrated that the topical application of prostaglandin analog F2a (PGF2a) reduced IOP in monkeys. Prostaglandins are classified by variations of their ring structure as well as the number and location of side-chain double bonds. 1-4 Prostaglandins belong to a chemical group called prostanoids, part of an even larger group called eicosanoids that is derived from 20-carbon arachidonic acid. When the first prostaglandin was discovered in 1936, it was thought to be a single substance, but subsequent investigations described a variety of these naturally occurring and synthesized compounds.
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