Dose-related interaction between timolol and adrenaline.

The effects on IOP of a combination of oral timolol maleate and adrenaline eye drops were investigated in a double-blind randomized trial using healthy volunteers. Timolol was given in two doses, 20 and 5 mg a day. One percent adrenaline eye drops were given to one eye, placebo to the other. The results showed a significant additive effect of adrenaline with the smaller dose of timolol, but with the larger dose of timolol the effect of adrenaline was antagonistic. These results may be due to an incomplete beta-blockade with the smaller dose of timolol, but a complete blockade with the larger dose.