Contra-indications Contra-indications For sildenafil General contra-indications: Hereditary degenerative retinal disorders; history of non-arteritic anterior ischaemic optic neuropathy; recent history of myocardial infarction; recent history of stroke Specific contra-indications: When used for Erectile dysfunction Avoid if systolic blood pressure below 90 mmHg no information available ; patients in whom vasodilation or sexual activity are inadvisable; recent unstable angina When used for Pulmonary arterial hypertension Sickle-cell anaemia Cautions For sildenafil General cautions: Active peptic ulceration; anatomical deformation of the penis e. This medicine usually begins to work for erectile dysfunction within 30 minutes after taking it. If you need emergency medical care for a heart problem, it is important that your doctor knows when you last took sildenafil. Push the plunger of the syringe, then insert the tip into the bottle while holding the bottle upright on a flat surface. If you take too much sildenafil or take it together with these medicines, the chance for side effects will be higher. · The effects may be increased because of slower removal of the medicine from the body. Leukemia (blood related cancer) or. Multiple myeloma (blood related cancer) or. Sickle-cell anemia (blood disorder)—Sildenafil should be used with caution in these patients as problems with prolonged erection of the penis may occur. The usual dose is 50mg, when you need it. Do not take it more than once a day. The dose can be increased to mg or decreased to 25mg depending on its effect. Take sildenafil up to 4 hours before you want to have sex. For sildenafil to work properly, you’ll need to be sexually excited. Maria Hudson. 4 hrs. ago. Anna Nelson. 6 hrs. ago. David Muldon. 8 hrs. ago.