Probably insignificant hepatic exposure.

(To be edited, initial data ST OCT 04) Timolol (betareceptor blocker) combined with carboanhydrase inhibitor dorzolamide, used as eyedrops to reduce the intraocular pressure in glaucoma. Dorzolamide is converted to N-desethyl dorzolamide which binds to carbanhydrase. Reaches circulation in topical application but due to effective binding to erytrocyte carboanhydrases the plasma levels are very low.

Uneventful use reported in 2 patients with acute porphyria.