Touching your eye can contaminate your drops, so this is critical. Zaditor Antihistamine Eye Drops Twin Pack 0.34 Fl oz 4.8 out of 5 stars 1,924. 2. 3. - If you have any further questions, ask your doctor, pharmacist or nurse. 4. They get to work within minutes and the effect of one dose lasts for 8 to 12 hours. Zaditen 0.25 mg/ml, eye drops, solution Ketotifen