Tip of the Month
Publishing date: March 2008
The Science behind the Tip
Although the ß-blocker timolol and the topical carbonic anhydrase inhibitor (CAI) dorzolamide both act by decreased aqueous humour production, they are almost completely additive in their effects on aqueous humour flow(1). Thus, the combination product Cosopt? has a powerful intraocular pressure (IOP) lowering effect of 32.7% at peak moment (i.e. time of maximal drug effect, 2 hours after drug application)(2). Similar effects on aqueous humour flow and IOP were observed in the 1980s with timolol and the oral CAI acetazolamide (Diamox?) taken together(3).
When a maximal IOP lowering effect is needed, it can be useful to switch from Cosopt® to + a topical ß-blocker. Diamox? is more effective as a suppressor of aqueous humour flow than dorzolamide(4-6) and dorzolamide has no additive effects in subjects already taking Diamox?(4,7).
Contributor: Ann Hoste, Antwerp
Co-editors: John Thygesen and Ann Hoste
Peer reviewers: Roger Hitchings and Anders Heijl
1. Wayman L, Larsson LI, Maus T, et al. Comparison of dorzolamide and timolol as suppressors of aqueous humor flow in humans. Arch Ophthalmol. 1997;115:1368-71.
2. Boyle JE, Ghosh K, Gieser DK, et al. A randomized trial comparing the dorzolamide-timolol combination given twice daily to monotherapy with timolol and dorzolamide. Ophthalmology. 1998;105:1945-51.
3. Dailey RA, Brubaker RF, Bourne WM. The effects of timolol maleate and acetazolamide on the rate of aqueous formation in normal human subjects. Am J Ophthalmol. 1982;93:232-7.
4. Maus TL, Larsson LI, McLaren JW, et al. Comparison of dorzolamide and acetazolamide as suppressors of aqueous humor flow in humans. Arch Ophthalmol. 1997;115:45-9.
5. Vanlandingham BD, Maus TL, Brubaker RF. The effect of dorzolamide on aqueous humor dynamics in normal human subjects during sleep. Ophthalmology. 1998;105:1537-40.
6. Larsson LI, Alm A. Aqueous humor flow in human eyes treated with dorzolamide and different doses of acetazolamide. Arch Ophthalmol. 1998;116:19-24.
7. Toris CB, Zhan GL, Yablonski ME, et al. Effects on aqueous flow of dorzolamide combined with either timolol or acetazolamide. J Glaucoma. 2004;13:210-5.
Tip Reviewer: Roger Hitchings
Tip Editors: Ann Hoste, John Salmon and John Thygesen