Verapamil is a vasodilator drug that belongs to the group of calcium antagonists or the group of calcium channel blockers. According to the Vaughan/Williams classification, verapamil is one of the antiarrhythmic agents.
What is verapamil?
Verapamil is an agent widely used to treat cardiac arrhythmias. Verapamil is an agent widely used to treat cardiac arrhythmias. Since the year 1983, the drug is part of the list of essential medicines. This list is maintained by the World Health Organization (WHO). Verapamil is available in the form of monopreparations or combination preparations. Commercially available preparations contain the drug in the form of racemate. This is a 1:1 mixture of enantiomers. The absorption of verapamil increases from 20% to 40% with continuous administration. A high first-pass effect is observed. The half-life of the drug is 3-7 hours. Excretion occurs via bile acids and the kidneys.
Pharmacologic effect
Verapamil is a calcium antagonist. Calcium antagonists decrease the influx of calcium ions into the interior of muscle cells. As a result, smooth muscle contracts less. As a result, the blood vessels dilate. Calcium influx into the voltage-dependent calcium channels of the heart is also blocked. Inhibition of calcium influx reduces the beating power of the heart muscle. This is also known as a negative inotropic effect. The heart‘s beating rate is also reduced. As a result, the oxygen demand of the heart is reduced, the blood pressure drops, the vessels are dilated and the heart is relieved. The widening of the vessels also makes more oxygen-rich blood available to the heart muscle. However, verapamil not only has a vasodilator effect, but also has a conduction-delaying effect in the AV node of the heart.
Medical use and application
Verapamil is commonly used in patients with coronary artery disease (CAD). Chronic stable angina, unstable angina, and spastic angina are also indications for the drug. Angina pectoris is defined as an attack-like pain in the chest. It is caused by a temporary disturbance in blood flow to the heart. In most cases, angina pectoris is caused by coronary heart disease. This in turn is caused by one or more narrowed coronary arteries. The drug is also used in patients after a heart attack. However, it is only used if there is no heart failure and beta-blockers cannot be used. Verapamil is one of the most important antiarrhythmic drugs. These are used to treat cardiac arrhythmias. Since the pulse rate is lowered, the drug can also be prescribed for atrial fibrillation or atrial flutter. In addition, verapamil is used to prevent cluster headaches. Very high doses are required to suppress the attacks. Since this can also affect the heart, regular ECG examinations must be performed when taking the drug. In rare cases, verapamil is used to lower blood pressure in arterial hypertension. In other countries, verapamil is also given for induratio penis plastica (penile curvature). Men with this condition experience severe pain during an erection due to an unnaturally severe bending of the penis. In Germany, verapamil is not approved for the treatment of this condition.
Risks and side effects
Adverse side effects include decreased heart rate, AV block (up to grade III AV block), low blood pressure, constipation, headache, and dizziness. The drug must not be used in shock, acute myocardial infarction and pronounced bradycardia. Sinus node syndrome, manifest heart failure, and atrial fibrillation in patients with Wolff-Parkinson-White syndrome (WPW syndrome) are also possible contraindications. Verapamil must also not be taken in cases of known hypersensitivity and in the first six months of pregnancy. Beta-blockers must also not be co-administered with the drug. Otherwise, AV block with a life-threatening drop in blood pressure may occur.In AV block I. Grade I AV block, low blood pressure, low pulse, impaired liver function, Lambert-Eaton syndrome, myasthenia gravis, and advanced muscular dystrophy, verapamil should be administered only under careful supervision. Since verapamil also passes into breast milk, it should be used in lactation only in exceptional circumstances. It should be noted that grapefruit may lead to enhanced absorption of verapamil when taken concomitantly. Thus, a stronger effect may occur. Diuretic drugs may also enhance the antihypertensive effect. With concomitant use of verapamil and cholesterol-lowering drugs in higher doses, the risk of suffering rhabdomyolysis increases. The dose of the cholesterol-lowering drug should be adjusted accordingly. Concomitant use of loperamide and verapamil may cause respiratory disturbances. Loperamide is used to treat diarrhea. If verapamil is taken, another drug should then be used if possible.
