[Effect of topical 8-hydroxy carteolol on intraocular pressure and melanin granules]

It was reported that 8-Hydroxycarteolol (8-OH CA), the major metabolite of carteolol hydroxychloride (CA), has a slightly different pharmacological effect from CA. We studied the reduction of intraocular pressure (IOP) on a single eyedrop application of 8-OH CA in albino and pigmented rabbit eyes. To determine the characteristic of 8-OH CA and CA, we investigated the binding ability of these drugs to synthetic melanin. In the present study, topically applied 2% CA did not significantly decrease IOP in albino and pigmented rabbit eyes. Topically applied 0.01, 0.05, 0.1 and 1.0% 8-OH CA significantly decreased the IOP of albino rabbit as did 0.1 and 1.0% 8-OH to pigmented rabbit eyes. The maximum reduction of IOP was 3.5 +/- 0.33 mmHg (mean +/- SEM) in albino rabbit and 3.0 +/- 0.45 mmHg (mean +/- SEM) in pigmented rabbit. Maximum IOP reduction was obtained after 30 min. from topical application in albino rabbit, but in pigmented rabbit after 1 hour or later. Our binding studies to melanin show that the melanin binding ability is less for 8-OH CA than for CA at any concentrations. These results may indicate that lower concentrations of topically applied 8-OH CA profoundly reduce IOP compared to CA, and 8-OH CA has less effect on melanin than CA.