Zenegra 100 mg (sildenafil 100 mg) can currently be bought from licensed online pharmacies and local pharmacies with a prescription. Tata 1mg – Zenegra 100 Tablet — currently lists the product from Alkem Laboratories Ltd. Apollo Pharmacy – Zenegra 100 mg — lists it as a prescription medicine. Zenegra 100 mg also lists the 4-tablet pack. A current shopping result also shows Zenegra 100 Tablet available from an online merchant. Zenegra 100 Tablet Important: 100 mg is the highest usual single dose of sildenafil and isn't appropriate for everyone. Do not take sildenafil with nitrate medicines (such as nitroglycerin) because the combination can cause a dangerous drop in blood pressure.