Various Antianginals

Various Antianginals

Write In Brief About Various Antianginals. Write Protocol For Management Of Acute Myocardial Infarction.
Answer:

Various antianginals in brief

Classification Of Antianginal Drugs

Nitrates:

• Short-acting: Glyceryl trinitrate
• Long-acting: Isosorbide dinitrate, isosorbide mononitrate, erythritol tetranitrate, penta erythritol tetranitrate.
  • β Blockers: Propranolol, metoprolol, atenolol and others
  • Calcium channel blockers: Verapamil, diltiazem, nifedipine, amlodipine, lacidipine.
  • Potassium channel opener: Nicorandil
  • Others: Dipyridamole, trimetazidine, ranolazine.

Antianginal Drugs Clinical Classification

• Used to abort or terminate attack: Glycer trinitrate, isosorbide dinitrate.
• Used for chronic prophylaxis: All other drugs.

Nitrates: Nitroglycerine and isosorbide dinitrate are given sublingually for an acute attack of angina. These are very fast-acting drugs and are useful in both types of angina—classical and variant. Nitrates can also be given for prophylaxis of angina by oral or transdermal route. Major limitations are low oral bioavailability (due to high first-pass metabolism) and the development of tolerance on long-term use. These can also cause hypotension which can be life-threatening in a patient taking sildenafil (for erectile dysfunction).

Beta-blockers: These are first-line drugs for prophylaxis of chronic angina. There are the only drugs that can decrease mortality in ischemic heart disease. However, these are contraindicated in variant angina as it is due to vasospasm and beta-blockers may aggravate coronary vasoconstriction by interfering with β2 mediated vasodilation. Limitations ofβ blockers include
the risk of bradycardia, hypotension, precipitation of asthma, and CHF. These should be avoided in diabetic patients because they can delay their recovery from hypoglycemia.

Various Antianginals: Types, Uses, and Mechanisms of Action

Calcium channel blockers: Verapamil, diltiazem and long-acting dihydropyridines like amlodipine can be used for prophylaxis of classical as well as variant angina. However, these do not decrease mortality whereas short-acting dihydropyridines like nifedipine can actually increase mortality due to reflex tachycardia.

Ranolazine: It is a new drug that acts by blocking a sodium channel thereby reducing calcium entry intracellularly. It also inhibits fatty acid oxidation. It is useful only for prophylaxis of angina. The advantage of ranolazine as compared to other antianginal drugs is that it has no effect on blood pressure (most other antianginal drugs can cause hypotension) and heart rate and can be safely used with drugs for erectile dysfunction (like sildenafil). The major limitation is a risk for the development of QT pro-location in ECG leading to Torsades’ de pointes (ventricular arrhythmia).

Antianginal Medications: Nitrates, Beta-blockers, and Calcium Channel Blockers

Protocol For Management Of Acute Myocardial Infarction

• Pain, anxiety, and apprehension: When the chest pain is not relieved by 3 doses of sublingual nitroglycerine given 5 min apart, myocardial infarction is suspected and an opioid analgesic (morphine/pethidine) or diazepam should be given parenterally.
• Oxygenation: By oxygen inhalation and assisted respiration, if needed.
• Maintenance of blood volume, tissue perfusion, and microcirculation: Slow IV perfusion of saline/low molecular weight dextran may be instituted if the BP falls, but volume overload is to be avoided.
• Correction of acidosis: It occurs due to lactic acid production; can be corrected by sodium bicarbonate IV infusion.
• Prevention and treatment of arrhythmia: Prophylactic IV infusion of β blocker (unless contraindicated due to fall in BP/bradycardia, etc.) is recommended. Its continuation orally for a few days has been shown to reduce the incidence of arrhythmias and mortality. β blockers used early in evolving myocardial infarction can reduce the infarct size (myocardial salvage) and subsequent
  complications. Tachyarrhythmias may be treated with lidocaine, procainamide, or amiodarone. Bradycardia and heart block may be managed with atropine or electrical pacing.
• Pump failure: The objective is to increase cardiac output and/or decrease filling pressure without unduly increasing cardiac work or lowering blood pressure. Drugs used for this purpose are:
  • Furosemide is indicated if pulmonary wedge pressure is > 20 mm Hg. It decreases cardiac preload.
  • Vasodilators: A vasodilator or combined dilator is selected according to the monitored hemodynamic parameters. Drugs like nitroglycerine (IV) or nitroprusside have been mainly used.
  • Inotropic agents: Dopamine or dobutamine IV infusion may be needed to augment the pumping action of the heart and tide over the crisis.
• Prevention of thrombus extension, embolism, and venous thrombosis: All patients with myocardial infarction should be immediately given aspirin (150-300 mg) for
  chewing and swallowing. This may be supplemented by other antiplatelet drugs (clopidogrel or prasugrel). Anticoagulants (heparin followed by oral anticoagulants) are used primarily to prevent deep vein thrombosis/ pulmonary embolism. Its value in checking coronary artery thrombus extension is uncertain. Any benefit is short-term; anticoagulants are not prescribed on a long-term basis now.
• Thrombolysis: Fibrinolytic agents, i.e. plasminogen activators streptokinase/urokinase/alteplase/tenecteplase to achieve reperfusion of the infarcted area. This is beneficial only when started within l to 2 hours of symptom onset. Primary percutaneous coronary intervention with stent placement is the preferred revascularization procedure now.
• Prevention of remodeling and subsequent CHF: ACE inhibitors/ARBs have proven efficacy and afford long-term survival benefits.
• Prevention Of Future Attacks
  • Platelet function inhibitors: Aspirin alone or combined with clopidogrel given on a long-term basis is routinely prescribed.
  • β blockers: Reduce the risk of reinfarction, CHF, and mortality. All patients not having any contraindications are put on a β1 blocker for at least 2 years.
  • Control of hyperlipidemia: Dietary substitution with unsaturated fats along with a statin hypolipidemic drug is recommended irrespective of plasma lipid levels.