Sildenalfil Sildenafil belongs to a group of medicines called Phosphodiesterase- 5 inhibitors. These open up the blood vessels, notably in the lungs to increase blood flow. With increased blood flow, more oxygen can be taken around the body to your muscles and organs. How to take it Sildenafil is taken three times a day, spaced out as best you can through the day, hence morning, mid-afternoon and bedtime. The most common dose is 20 or 25mg three times daily but higher doses may also be used for certain patients. Sildenafil is available as 20mg, 25mg, 50mg and 100mg tablets and a liquid medicine. Do not take sildenafil if you: • Have had an allergic reaction to sildenafil in the past. • Are taking medicines called nitrates for chest pain (for example GTN spray). • Have a serious heart or liver problem. • Have recently suffered a stroke or heart attack. • Have low blood pressure. • Have a rare inherited eye condition, such as retinitis pigmentosa. Side effects Side effects with sildenafil causing people to stop treatment are quite rare. However the most common side effects are headache, flushing, nasal congestion, nosebleeds, indigestion, low blood pressure and changes to your vision (especially the way you see different colours). Talk to your PH centre if you notice any change in your vision. Other useful information Sildenafil is only available on prescription. The dosage prescribed for men with impotence is different to your dose for PH. Simply taking sildenafil will not cause men with PH to have erections, as you need to be aroused for it to work in that way. If you forget to take a dose of sildenafil, take it as soon as you remember but never take a double dose to make up for the missed one.