Antianginal drugs are medications used to manage and alleviate the symptoms associated with angina pectoris. Angina is chest pain that arises when the heart muscle does not receive enough oxygen-rich blood. These medications work to restore a better balance between the heart’s oxygen supply and its demand, thereby reducing discomfort. Their objective is to lessen the frequency and intensity of angina episodes, improving quality of life.
Understanding Angina
Angina pectoris is a symptom indicating the heart muscle is not getting sufficient blood and oxygen, rather than being a disease itself. This sensation commonly manifests as a squeezing, pressure, or heaviness in the chest, though it can also radiate to the arms, neck, jaw, or back. This imbalance frequently occurs when the coronary arteries, which supply blood to the heart, become narrowed. This narrowing is often due to the buildup of fatty deposits called plaque, a condition known as atherosclerosis. When the heart’s workload increases, such as during physical activity or stress, narrowed arteries may fail to deliver enough oxygenated blood, leading to angina symptoms, similar to a partially clogged fuel line struggling under increased engine demand.
General Mechanisms of Antianginal Drugs
Antianginal drugs achieve this through two broad strategies: increasing the supply of oxygenated blood to the heart or decreasing the heart’s overall demand for oxygen. One approach involves widening blood vessels, a process known as vasodilation. This action can increase blood flow to the heart muscle, thereby boosting oxygen supply. The other main strategy focuses on reducing how hard the heart has to work. This can be accomplished by slowing the heart rate, reducing the force of the heart’s contractions, or decreasing the pressure the heart must pump against.
Common Classes of Antianginal Drugs
Nitrates
Nitrates relax vascular smooth muscle throughout the body, leading to vasodilation. This effect is largely mediated by increasing nitric oxide, which then triggers a cascade leading to blood vessel widening. Nitrates preferentially dilate veins, which reduces the amount of blood returning to the heart (preload), thereby decreasing the heart’s workload and oxygen demand. They also dilate coronary arteries, which can increase blood flow and oxygen supply to the heart muscle. Common examples include nitroglycerin (e.g., Nitrostat or Nitro-Dur), isosorbide dinitrate (e.g., Isordil), and isosorbide mononitrate (e.g., Imdur); short-acting forms like sublingual nitroglycerin are used for acute relief, while longer-acting formulations prevent attacks.
Beta-blockers
Beta-blockers, also known as beta-adrenergic blocking agents, work by blocking the effects of stress hormones like epinephrine (adrenaline) and norepinephrine on specific receptors in the heart. By blocking these receptors, beta-blockers slow the heart rate and reduce the force of the heart’s contractions. This action significantly lowers the heart’s oxygen demand, making them effective for long-term angina prevention. Common generic examples include metoprolol (Lopressor, Toprol XL), atenolol (Tenormin), and propranolol (Inderal LA). They are generally not used for immediate relief of an acute angina attack.
Calcium Channel Blockers
Calcium channel blockers (CCBs) function by inhibiting the movement of calcium into the cells of the heart and blood vessel walls. Calcium plays a significant role in muscle contraction, so by blocking its entry, CCBs cause blood vessels to relax and widen, leading to vasodilation. This dilation increases blood flow to the heart and reduces the pressure the heart pumps against. Some CCBs, like verapamil (Calan) and diltiazem (Cardizem), also slow the heart rate and reduce the heart’s contractile force, further decreasing oxygen demand, while others, such as amlodipine (Norvasc) and nifedipine (Procardia), primarily cause vasodilation with less direct effect on heart rate. They are used for various types of angina, including stable angina and Prinzmetal’s angina (coronary artery spasm).
Ranolazine
Ranolazine, sold under the brand name Ranexa, represents a different class of antianginal medication. Ranolazine is thought to inhibit the late sodium current in heart muscle cells, which can reduce an overload of calcium within these cells. This action helps to reduce the tension in the heart wall and, consequently, the heart’s oxygen requirements, without significantly affecting heart rate or blood pressure. Ranolazine is typically prescribed for chronic angina, often as an add-on therapy when other medications are not fully effective.
Potential Side Effects and Drug Interactions
Antianginal drugs can cause side effects. Nitrates commonly lead to headaches, dizziness, and flushing due to their vasodilatory effects; low blood pressure and a reflex increase in heart rate can also occur. Beta-blockers may cause fatigue, slow heart rate (bradycardia), cold hands or feet, and dizziness, with some individuals experiencing sleep disturbances or sexual dysfunction. For calcium channel blockers, common side effects include constipation (with non-dihydropyridine types), dizziness, flushing, headaches, and swelling in the feet or lower legs (with dihydropyridine types). Ranolazine’s most frequently reported side effects include dizziness, headache, constipation, and nausea.
A particularly serious drug interaction involves nitrates and phosphodiesterase-5 (PDE5) inhibitors, such as sildenafil (Viagra), tadalafil (Cialis), or vardenafil (Levitra), used for erectile dysfunction. Both nitrates and PDE5 inhibitors cause vasodilation, and taking them together can lead to a severe and life-threatening drop in blood pressure. This combination is generally contraindicated. Individuals should inform their healthcare provider about all medications they are taking, including over-the-counter drugs and supplements. Always discuss side effects or concerns with a doctor or pharmacist, and never stop prescribed medication without medical advice.