<prompt> Sildenafil should not be used inDiabeticsPatients on vasodilator therapyPulmonary hypertensionErectile dysfunction  <response>: Sildenafil inhibits PDE-5 and prevents Nitric oxide NO degradation. Increased NO results in vasodilation. It should not be used in patients taking vosodilators as it can lead to sudden hypotension. 