Prostaglandin analogues in the treatment of glaucoma

Prostaglandin (PG) analogues are a new class of ocular hypotensive drugs th at have been developed for the treatment of open angle glaucoma. Two of the se drugs, latanoprost and unoprostone, are presently commercially available . Latanoprost was introduced in 1996 in the US and Europe. Presently it enjoy s the most widespread use and is the most well documented drug of this grou p. It reduces the intraocular pressure (IOP) by a mechanism of action diffe rent from other drugs; namely by increasing the uveoscleral outflow. The aq ueous inflow is not affected. The optimal dose regimen is one drop of 50 mu g/ml once daily, which reduces the IOP by approximately 30% in patients wi th glaucoma. A more pronounced ocular hypotensive effect is demonstrated wh en latanoprost is combined with other glaucoma therapies, including beta-bl ockers, adrenergic and cholinergic agonists or carbonic anhydrase inhibitor s. Latanoprost is well tolerated. The drug reaches a plasma concentration b elow that needed for stimulation of the FP-receptor, which may explain its favourable systemic tolerability profile. The major ocular adverse effect i s increased iris pigmentation, which is due to increased synthesis of melan in in the melanocytes of the iris stroma. It is most frequently seen in gre en-brown eyes and it is probably permanent. A low frequency of cystoid macu lar oedema has also been reported, predominantly in predisposed eyes. Unoprostone was launched in Japan in 1994, but there is little experience w ith this drug outside the Japanese market and the documentation is more lim ited. Its main mechanism of action is on outflow, but this is not yet fully elucidated. The recommended dosage regimen is 1 drop of 1.2 mg/ml twice da ily. No comparative studies in humans between the 2 drugs have yet been pub lished.