• The chronic use of timolol (Timoptic) maleate to control glaucoma may produce cytotoxic complications in the cornea. We have therefore compared the relative toxic effects of the commercial ophthalmic preparation with that of the pure compound. Commercial vehicle, either with or without 16mM timolol maleate, killed cultures within the first five minutes of exposure. Pure timolol maleate, however, caused rapid but reversible cellular contractions, and cells remained viable in it for over 24 hours. Dilution with culture medium reduced both the cytotoxicity and the speed of the contractions. Incubation in 1:100 dilutions of vehicle or commercial drug preparations or in 0.16mM pure timolol maleate did not alter cellular morphology. The results indicate that while undiluted vehicle is toxic, timolol maleate is not.
Staatz WD, Radius RL, Van Horn DL, Schultz RO. Effects of Timolol on Bovine Corneal Endothelial Cultures. Arch Ophthalmol. 1981;99(4):660-663. doi:10.1001/archopht.1981.03930010660012