Antianginal drugs
Angina pectoris
I- Overview
Angina pectoris : a characteristic chest pain causd by coronary blood flow that is insuffecient to meet the oxygen demands of the myocardium
The impalance between oxygen delivery and utilization may result from
a) a spasm of the vascular smooth muscle
b) obstruction of blood vessels caused by atherosclerotic lesions
Characters of angina :sudden severe pressing substernal pain radiating to the left arm
Three classes of drugs are effective either alone or in combination,in treating patients with stable angina
Nitrates : decrease coronary vasoconstriction or spasm and increase perfusion of the myocardium by relaxing coronary arteries
B blockers : decrease the oxygen demands of the heart
Calcium channel blockers
Prinizimetals angina :a variant angina caused by spontaneous coronary spasm either at work or at rest ...rather than by increases in myocardial oxygen requirements
It is controlled by organic nitrates or calcium channel blockers but B blockers are contraindicated
II- Organic nitrates & nitrites
these compounds cause a rabid reduction in myocardial oxygen demand followed by rapid relief of symptoms
A- Nitroglycerin
its sublingual or spray forms are the drug of choice used for prompt relief of ongoing attagk of angina precipitated by excercise or emotional stress
Effects on cardiovascular system
at therapeutic doses :has 2 major effects
a) Dilation of the large veins resulting in pooling of blood in the veins which diminish the preload(discussed before) and reduces the work of the heart
b) Dilates the coronary vasculature providing increased blood supply to the heart muscle
The total effect is a decrease in myocardial oxygen cosumption because of decreased cardiac work
Adverse effects
long acting preparations cause headache in about 30% - 60% of patients
high doses can cause postural hypotension,flushing &tachycardia
B- Isosorbide dinitrate'
has a lower potency than nitroglycerin in relaxing vascular smooth muscle - can be used orally
III- B adrenergic blockers
Supress the activation of the heart by blocking B1 receptors
reduce the work of the heart by decreasing cardiac output and causing a slight decrease in blood pressure
Reduce the frequency and severity of angina attacks
Particullary useful in the treatment of patient with myocardial infarction
Contraindications
in diabetes
peripheral vascular disease
chronic obstructive pulmonary disease
IV- Calcium channel blockers
Inhibit the entrance of calcium into cardiac and smooth muscle cells of the coronary and systemic arterial beds so
All of them are vasodilators and decrease smooth muscle tone and vascular resistance
A- Nifedipine
Mainly,an arteriolar vasodilator
Exerts greater effect on cardiac conduction and heart rate
Used in variant angina
B- Verpamil
Slows cardiac conduction directly which decrease the heart rate and the oxygen demand
Has negative inotropic effects greater than that of nifedipine but weaker as a vasodilator
Contraindications
in preexisting depressed cardiac function
in atrioventricular conduction abnormalities
Adverse effects
Used with caution in digitalis patients...discussed before
Constipation
C-Deltiazem
Its cardiovascular effects similar to verpamil
Reduce the heart rate but lesser than verpamil
Reduce blood pressure
Relieve coronary artery spasm so used in variant angina
Can be used in angina in patients with concomitant diseases