Mechanism of action:
1. Nitrates cause relaxation of the coronary vessels resulting in the decreased constriction of coronary vessels. The decreased constriction of the coronary arteries leads to increased transfusion of blood to the muscles of the heart (improved letting of blood).
2. On the other hand, it promotes dilation of the capacitance veins resulting in the decreased venous return to the heart due to pooled effect of blood in the veins. This decreased venous return to the heart decreases oxygen demand of the muscles of the heart.
Relaxation occurs in all segments of vascular system:
1. Less dilation of the arterioles and precapillary sphincters due to reflex responses.
2. They reduces cardiac output.
4. Organonitrates causes relaxation of the arteries resulting in the reduced systemic arterial pressure causing reduced afterload of the heart leading to the reduced cardiac oxygen requirement.
5. Organonitrates causes relaxation of the veins resulting in the reduced preload causing reduced myocardial wall tension leading to reduced myocardial oxygen requirement.
Other smooth muscle organs:
Organonitrates have short duration of action on the relaxation of the smooth muscles i.e. esophageal and biliary smooth muscle.
Nitrite ion may cause pseudocyanosis and tissue hypoxia.
1. Stable and unstable angina pectoris
2. Variant angina pectoris
3. Orthopnea and Paroxysmal nocturnal dyspnea
4. Cyanide poisoning
Facial flushing (due to cutaneous vasodilation), Severe type of headache (due to vasodilation of cerebral vessels leading to elevated intracranial pressure and headache), Orthostatic hypotension, dizziness, weakness