The People's Perspective on Medicine

Verapamil (slow release)


Calan belongs to a class of medicines called calcium channel blockers.

Because of their safety and effectiveness, these drugs have helped revolutionize the treatment of high blood pressure.

Other uses of calcium channel blockers include treatment of irregular heart rhythms and angina.

There is even some preliminary research that suggests some of these compounds may be able to prevent migraine headaches, ease nighttime leg cramps, asthma and Raynaud’s disease, and perhaps reduce atherosclerosis.

Despite these future possibilities, Calan SR has been approved only for the treatment of hypertension.

Side Effects and Interactions

One of the most common side effects of Calan is constipation. Although bothersome, this can often be controlled with fluid and fiber or a bulk-forming laxative such as psyllium.

Another reaction to be alert for is low blood pressure, which may show up as lightheadedness and dizziness.

Although uncommon, other adverse reactions include headache, fluid retention leading to swelling of arm and legs, nausea, tiredness, rash and slowed heart rate. Report any symptoms or suspected side effects to your physician promptly.

Calan can interact with a number of other drugs, including several that are used to treat high blood pressure or heart conditions, the asthma medicine theophylline, the anticonvulsant Tegretol, the transplant medication Sandimmune and the anti-tuberculosis agent rifampin.

The popular antidepressant Prozac may increase the likelihood of side effects from Calan.

Over-the-counter calcium supplements can reduce the effectiveness of Calan. Check with your doctor and pharmacist to make sure Calan is safe in combination with any other drugs you take.

Special Precautions

Although Calan may be prescribed for a variety of cardiac indications, there are some serious heart conditions that may be worsened by this drug.

Your doctor should be fully informed about any heart problem, kidney disease, liver disease, low blood pressure and muscular dystrophy.

Careful monitoring is called for in any of these cases due to an increased risk of toxicity.

In addition, older people may be more sensitive to the blood-pressure-lowering effects of Calan SR.

Taking the Medicine

The manufacturer recommends that this sustained-release formulation should be taken with food, preferably in the morning with breakfast.

If a second dose is needed it should be swallowed approximately 12 hours later.

Do not stop taking Calan SR suddenly, as this could lead to complications.

Your doctor will tell you how to taper off gradually if you no longer need this medication.

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About the Author
Joe Graedon is a pharmacologist who has dedicated his career to making drug information understandable to consumers. His best-selling book, The People’s Pharmacy, was published in 1976 and led to a syndicated newspaper column, syndicated public radio show and web site. In 2006, Long Island University awarded him an honorary doctorate as “one of the country's leading drug experts for the consumer.” .
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I’m taking the generic Verapamil ER for blood pressure and angina. My Dentist tells me that it can increase cavities because it causes saliva to thicken. If that is so; Can it also thicken Phlegm? I have COPD and since I started the Med I’ve had a hard time clearing my throat. Also seem to be making more trips to the bathroom at night despite my GP’s insistence that it’s not a diuretic.

Recently my Prescription Drug Insurance denied coverage for Calan SR – which I have been taking for a number of years – substituting the generic Verapamil ER. Subsequently I have experienced increased incidence of x-systoles.
For the past 4 days I have been taking the Calan SR (purchased privately) with no noted side effects. Do you have any information as to differences between the the Brand and the Generic as mentioned above?
I am under the active supervision of my physician and I take the medication as instructed.

Since taking verapamil, it has lowered BP, but occasionally feel short of breath and tired. Then it passes, not sure if it is the medication or been recently diagnosed with A. Fib

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