Timolol: Potential for additive effect w/ oral Ca channel blockers, β-adrenergic blocking agents, antiarrhythmics (including amiodarone), digitalis glycosides, parasympathomimetics, guanethidine. Decreased response to adrenaline. Potentiated hypertensive reaction to sudden w/drawal of clonidine. Potentiated systemic β-blockade w/ CYP2D6 inhibitors (eg, quinidine, fluoxetine, paroxetine). Increased hypoglycaemic effect of antidiabetic agents. Mydriasis w/ adrenaline. Brinzolamide: Potential for additive effect w/ oral carbonic anhydrase inhibitor. Inhibited metabolism w/ CYP3A4 inhibitors eg, ketoconazole, itraconazole, clotrimazole, ritonavir & troleandomycin.