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Antianginal drugs are used to treat Angina Pectoris (chest pain) which is a symptom of ischemic heart disease. Due to anigina pectoris heart do no get the required amount of oxygen and nutrients and fails to work to properly. In this Note, we will learn about the Classification, Mechanism of Action, Adverse Effects, Advantages and Drug Interection of antianginal drugs.
What is Angina Pectoris ?
Anginal pectoris disease affect the coronary arteries which supply oxygenated blood from left
ventricle to heart tissues. In angina pectoris the lumen of artery become restricted and it becomes less efficient in supplying the blood and oxygen to heart called as ischemia.
The following two types of angina are mainly seen:
1) Classic Angina (Angina of Exercise): This angina pain occurs w hen the demand of oxygen exceeds the s upply of oxygen, most commonly due to diminished coronary flow.
2) Vasospastic (Prinzmetal’s or Variant) Angina: This angina pain occurs at rest and is characterised by reversible coronary vasospasm , which in turn reduces the supply of oxygen
Some individuals however show mixed angina, characterised by both exercise induced and resting attacks of angina.
Symptoms of Angina Pectoris includes:
- Shortness of breath
Classification of Antianginal Drugs
The antianginal drugs are are classified between the following types:
- Short acting: Glyceryl trinitrate (GTN)
- Long acting: Isosorbide dinitrate, Isosorbide mononitrate ,Erythrityl tetranitrate, Pentaerythrityl tetranitrate
- β Blockers: Metoprolol, Atenolol, Bisoprolol, Celiprolol
- Cytoprotective Drugs: Trimetazidine, Ranolazine.
- Potassium Channel Opener: Nicorandil, Pinacidil, Cromakalim,Minoxidil, Diazoxide
- Calcium Channel Blockers:
- Verapamil, Diltiazem
- Dihydropyridine —Nifedipine, Amlodipine, Nitrendipine,Nimodipine
Antianginal Drugs – Nitrates
Organic nitrites and nitrates are simple nitric and nitrous acid esters of glycerol having different
volatilities (e.g., isosorbide dinitrate and isosorbide mononitrate are solids at room temperature, nitroglycerine is moderately volatile, and amyl nitrite is highly volatile). These compounds are used in angina pectoris. They rapidly reduce the myocardial oxygen demand, followed by rapid relief of symptoms. They are effective in classic as well as in variant angina pectoris.
Mechanism of Action
Nitrates inhibit coronary vasoconstriction or spasm as a result of which perfusion of the myocardium increases, thus, relieving vasospastic angina. Nitrates also cause venodilation, resulting in decreased preload and myocardial oxygen consumption. Due to this action, nitrates are effectively used in classic angina
Therapeutic uses of Nitrates are given below:
- Angina pectoris
- Acute coronary syndromes
- Myocardial infarction (MI)
- CHF and acute LVF
- Biliary colic
- Esophageal spasm
- Cynaide poisoning
The most common toxic effects of nitrates are the responses evoked by vasodilation.
- These include tachycardia (from the baroreceptor reflex)
- Orthostatic hypotension (a direct extension of the venodilator effect), and
- Throbbing headache from meningeal artery vasodilatation.
Nitrates + Sildenafil can lead to severe hypotension, myocardial infarction and death.
Antianginal Drugs – Calcium Channel Blockers
Calcium channel blockers invariably block L-type Ca2+ channel, and decrease heart rate, contracitility and conduction velocity. They also reduce left-ventricular filling pressure, which reduces workload and overall oxygen demand of the heart.
Mechanism of Action
Calcium channel blockers act by blocking the voltage -sensitive calcium channels. They act on the inner side of the membrane and bind to the channels in depolarized membrane .
As a result of drug binding , the channels open rarely after depolarization. A marked decrease in trans membrane Ca2+ion current relaxes the smooth muscles.
Calcium channel blockers are used for the treatment of stable as well as variant angina. In variant angina, they cause relaxation of coronary artery spasm , thus increasing the cardiac oxygen supply; while in stable angina, they cause relaxation of peripheral arterioles, resulting in decreased after load and cardiac oxygen demand. Verapamil and Diltiazem moderately reduce oxygen demand by suppressing the heart rate and contractility.
Calcium channel blockers give rise to cardiovascular adverse effects. Blood pressure reduces due to dilation of peripheral arterioles , resulting in induced reflex tachycardia. This reaction mainly occurs with nifedipine and rarely with verapamil and diltiazem. Due to their suppressant effects on the heart, verapamil and diltiazem should be used carefully in patients taking β-blockers and suffering from bradycardia, heart failure, or AV block.
Antianginal Drugs – β Blockers
β blockers are the drugs that block the action of cathecholamines through β receptors. Some β Blockers drugs are Timolol, metoprolol, atenolol, and propranolol.
Mechanism of Action
The β-adrenergic antagonists decrease the oxygen demand by reducing the heart rate. They oppose sympathetic stimulation , which increases heart rate, contraction force, and oxygen rate.
The β-adrenergic antagonists in combination with nitrates are used for the treatment of angina pectoris. Persistent angina can be trea ted using drugs from two or more classes, i.e., β adrenergic blockers combined with long -acting nitrates or calcium channel blockers.
The β-adrenergic antagonists due to their antihypertensive action are ideal for patients having hypertension and coronary artery disease. They are the drugs of choice for the prophylaxis of chronic angina
The adverse effects of β-adrenergic antagonists are hypotension, bradycardia, insomnia (inability to sleep), bizarre dreams, diminished sex drive, impotence, and depression.
Antianginal Drugs – Potassium Channel Openers
The potassium channel openers which were used earlier for the treatment of severe hypertension and hypertensive eme rgencies are minoxidil and diazoxide; but use of these agents has been reduced after synthesis of some novel potassium channel openers, like nicorandil, pinacidil, and cromakalim.
Mechanism of Action
- These drug opens the ATP – sensitive K channels
- Opening of this leads to hyper polarization
- Followed by closing of calcium channels
- Less intracellular calcium — muscle relaxation
Potassium channel openers are used in patients who have undergone optimal management with other d rugs, but still remain symptomatic, often while they await surgery or angioplasty.
Common adverse effects o f potassium channel openers are flushing, palpitation, weakness, headache, mouth ulcers, nausea, and vomiting.
Newer Antianginal Drugs
Some new antianginal drugs are discussed below:
Ranolazine: This drug reduces the number of angina episodes per week and increases exercise tolerance. These benefits were however moderate and smaller in women than in men.
Trimetazidine: It is an anti -ischemic (anti-anginal) metabolic agent. It improves myocardial glucose utilization by inhibiting fatty acid metabolism.
Dipyridamole: It is a powerful coronary dilator; increases total coronary flow by preventing uptake and degradation of adenosine.
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