Timolol eye drops: bradycardia or tachycardia?

26 eyes of 14 patients--8 with primary open angle glaucoma, 6 glaucoma suspects--were treated for at least 6 months with either twice daily timolol 0.25% in both eyes or twice daily timolol 0.50% in one eye. None of the patients received concomitant local or oral drugs. Special attention was paid to tachyphylaxis and to blood pressure and pulse rate. We could detect a slight although not significant tendency to tachyphylaxis (1-2 mm Hg) after 1 week of timolol treatment. It takes at least 1-2 weeks to reach the initial I.O.P. level after withdrawal of timolol therapy. Blood pressure did not change significantly. The pulse rate showed a slight although not significant tendency to decrease (a few beats/minute), but we detected a reflex tachycardia (10 beats/minute) after withdrawal of timolol therapy which was very significant. This rebound phenomenon has not been referred to in the literature. It seems reasonable to conclude that one should take care in treating glaucoma patients with concomitant arrhythmias with timolol eye drops.