Verapamil, which may be sold under brand names like Calan® or Isoptin®, is a calcium antagonist or calcium channel blocker (CCB) used to treat conditions like high blood pressure, heart arrhythmias, angina, or certain types of migraines. It also has been investigated in off-label use for the treatment of bipolar disorder, and potentially as adjunct treatment for malaria. The action of this medicine is best understood as it relates to high blood pressure. The drug helps to regulate blood pressure by widening arteries, which is accomplished by inhibiting flow of calcium into the blood vessels and the circulatory system. Like all medications, verapamil isn’t appropriate for everyone, and has noted side effects, contraindications, and drug interactions.
Verapamil is usually sold in generic form and it’s available in oral tablets of varying kinds. It’s also used in hospital settings where it may be infused intravenously. In pill form, the drug may come in several dose strengths, including some extended release formulations, and dosage is different depending on condition for which it is prescribed. The medication has been fairly well studied because it has been on the market since the early 1980s, though present off-label and investigatory uses are recent.
Sometimes this medication is contraindicated. People with low blood pressure, kidney or liver disease, heart failure, recent heart attack, and heart block without a pacemaker generally cannot use verapamil. There is conflicting evidence on use of this medication during pregnancy. It is sometimes used as an alternative to mood stabilizers like carbamazepine, valproic acid, or lithium because it is considered less tetrogenic with some mood stabilizing action. Still, if its use can be avoided during pregnancy, this is advisable because its effects have not been fully studied.
There are certain medications that may interact or interfere with verapamil. These include antacids like cimetidine, mood stabilizers like carbamazepine and lithium, many other medications for heart conditions, some antivirals, certain antibiotics, a variety of antifungal medications, and many drugs used to treat cancer. Patients should have a full list of all medications taken to present to physicians so that best drug choice is possible. People should also avoid drinking grapefruit juice for several hours before and after taking any CCB since this may affect how well the body absorbs these medicines.
Common side effects of verapamil include sexual dysfunction, loss of libido and potential for erectile dysfunction. Additional adverse effects that are commonly reported are flushing, headache, dizziness or sleepiness, rash, stomach upset, and constipation. More serious side effects need emergency medical attention, and these include anaphylactic shock (brought on by drug allergy), dramatic changes in heart rhythm (fast or slow), severe skin rash, sudden onset of flulike symptoms, shortness of breath, yellow skin and eyes, low urinary output, and weight gain or sudden swelling that is rapid.
Patients should also discuss with doctors if less serious side effects continue to create problems. It’s possible that another drug can more appropriately treat symptoms with fewer complications. On the other hand, many people tolerate verapamil well.