<s>[INST] context: CALCIUM CHANNEL BLOCKERS-Patients who respond to shoacting vasodilators at the time of cardiac catheterization (a fall in mean pulmonary aerial pressure >=10 mmHg and a final mean pressure <40 mmHg) should be treated with calcium channel blockers. Typically, these patients require high doses (e.g., nifedipine, 240 mg/d, or amlodipine, 20 mg/d). Patients may have dramatic reductions in pulmonary aery pressure and pulmonary vascular resistance associated with improved symptoms,regression of RV hyperophy, and improved survival now documented to exceed 20 years. ENDOTHELIN RECEPTOR ANTAGONISTS The endothelin receptor antagonists bosentan and ambrisentan are approved treatments of PAH.Because of the high frequency of abnormal hepatic function tests associated with these drugs, primarily an increase in transaminases, it is recommended that liver function be monitored monthly throughout the duration of use.Bosentan is contraindicated in patients who are on cyclosporine or glyburide concurrently. PHOSPHODIESTERASE-5 INHIBITORS Sildenafil and tadalafil , phosphodiesterase-5 inhibitors, are approved for the treatment of PAH. Phosphodiesterase-5 is responsible for the hydrolysis of cyclic GMP in pulmonary vascular smooth muscle, the mediator through which nitric oxide lowers pulmonary aery pressureand inhibits pulmonary vascular growth. PROSTACYCLINS I loprost, a prostacyclin analogue, is approved inhalation for PAH. It has been shown to improve a composite measure of symptoms and exercise tolerance by 10% ref:Harrison&;s principles of internal medicine,ed 18,pg no 2079. [/INST] question: Drug Not used in pulmonary hypeension - | options: A: Calcium channel blocker B: Endothelin receptor antagonist C: Alpha blocker D: Prostacyclin | answer: C </s>