Diltiazem: How it works, Uses, Dosage, Side Effects, FAQs

What is diltiazem?

Diltiazem more commonly known by the Cardizem CD and Taztia XT is a prescription drug used to treat high blood pressure. If you have high blood pressure, taking diltiazem helps to prevent future heart disease, heart attacks, and strokes.

Diltiazem is also used to prevent chest pain caused by angina as well as Raynaud’s phenomenon. It can also be used to help heal an anal fissure.

It’s available on prescription only and comes as tablets, capsules, cream, or ointment. Diltiazem is also available as an extended-release capsule, an extended-release tablet, and an intravenous (IV) solution, which is only given by a healthcare professional. Diltiazem was approved for medical use by the FDA in 1982.

How does Diltiazem work?

Diltiazem is a benzothiazepine derivative with antihypertensive and vasodilating properties. It is a member of the non-dihydropyridine calcium channel blockers drug class that works through various mechanisms of action, but it primarily works by inhibiting the calcium influx into cardiac and vascular smooth muscle during depolarization.

How long does diltiazem take to work?

Diltiazem starts to work on the day you start taking it. Diltiazem is absorbed from the tablet formulation to about 98% of a reference solution. Single oral doses of 30 to 120 mg of Diltiazem result in detectable plasma levels within 30 to 60 minutes and peak plasma levels 2 to 4 hours after drug administration.

However, for high blood pressure and angina, it may take a couple of weeks to experience the full effects of Diltiazem.  If you’re taking diltiazem for high blood pressure, you may not have had any symptoms before. In this case, you may not feel any different when you take it.

How should Diltiazem be used?

Diltiazem comes as a tablet, an extended-release (long-acting) tablet, and an extended-release capsule to take by mouth. The regular tablet is usually taken three or four times a day. The extended-release capsule and tablet are usually taken one or two times a day. Ask your pharmacist if you should take diltiazem with or without food, because instructions may vary with each product. Take diltiazem at around the same time(s) every day.

Diltiazem is taken four times a day. The total amount in a day typically ranges from 180–360 mg.

Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take diltiazem exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

Swallow the extended-release capsules and tablets whole; do not chew or crush them.

Your doctor will probably start you on a low dose of diltiazem and gradually increase your dose, not more than once every 7 to 14 days if you are taking the extended-release tablet or capsule and not more than once every 1 to 2 days if you are taking the regular tablet.

If taken regularly, diltiazem may control chest pain, but it does not stop chest pain once it starts. Your doctor may give you a different medication to take when you have chest pain.

Diltiazem controls high blood pressure and chest pain (angina) but does not cure them. It may take up to 2 weeks before you feel the full benefit of diltiazem. Continue to take diltiazem even if you feel well. Do not stop taking diltiazem without talking to your doctor.

What are the side effects of diltiazem?

Diltiazem may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

•          constipation

•          cough

•          diarrhea

•          dizziness or lightheadedness

•          flushing

•          headache

•          nasal congestion

•          slow heartbeat

•          vomiting

•          weakness

Some side effects can be serious. If you experience any of the following symptoms, call your doctor immediately or get emergency medical treatment:

•          difficulty breathing or swallowing

•          extreme tiredness

•          fainting

•          flu-like symptoms

•          increase in frequency or severity of chest pain (angina)

•          lack of energy

•          loss of appetite

•          nausea

•          pain in the upper right part of the stomach

•          rash

•          swelling of the face, eyes, lips, tongue, hands, arms, feet, ankles, or lower legs

•          unusual bleeding or bruising

•          yellowing of the skin or eyes

If you experience a serious side effect, you or your doctor may send a report to the Food and Drug Administration’s (FDA) MedWatch Adverse Event Reporting program online ( or by phone (1-800-332-1088).

Frequently Asked Questions On Diltiazem

Can you split diltiazem tablets?

Yes, you can split diltiazem tablets. The immediate-release tablets may be split along the line down the center (score line). Don’t crush, chew, or break extended-release tablets or capsules. If you find tablets or capsules difficult to swallow, speak to a pharmacist or doctor, as there may be other options.

Why take diltiazem on empty stomach?

Diltiazem can be given in a tablet or capsule form. The tablets and capsules are not interchangeable; do not use both. The tablets should be taken on an empty stomach, about half to one hour before food. But studies have shown that food does not influence the bioavailability of diltiazem administered as a conventional tablet or as a slow-release formulation.

What is the best time of day to take diltiazem?

Studies have shown that diltiazem is better and more effective when administered in the evening or at bedtime than the traditional morning dosing because of the increased risk of myocardial ischemia in the morning hours. The ER formulation can be taken either in the morning or at bedtime and will work best if you take it at the same time each day.

Does diltiazem lower your heart rate?

Yes, though uncommon, diltiazem can lower your heart rate. In some cases, it may make your heart rate too low, causing you to feel tired or weak. If this happens, you should seek medical attention.

Is diltiazem hard on the kidneys?

No, studies indicate that diltiazem monotherapy has no overall effect on glomerular filtration rate, renal plasma blood flow, salt, and water excretion, or body fluid composition. However, diltiazem can reduce renal vascular resistance. The decrease in renal vascular resistance leads to increased peritubular hydrostatic pressure.

Is diltiazem a blood thinner?

No, diltiazem is not a  blood thinner but a calcium channel blocker. It works by affecting the movement of calcium into the cells of the heart and blood vessels. This relaxes the blood vessels, lowers blood pressure, and increases the supply of blood and oxygen to the heart while reducing its workload.

Does diltiazem cause weight gain?

Yes, diltiazem can cause sudden weight gain or swelling in the arms or legs. Call your doctor right away if you have noticed these side effects.

How much diltiazem is fatal?

Diltiazem overdose has been reported previously, mainly as case reports and in a few case series. In particular, the overdose of its slow release formulations may lead to severe toxicity if appropriate decontamination is not started.

Diltiazem overdose can result in rapid progression to hypotension, bradydysrhythmia, and cardiac arrest, while overdoses of extended-release formulations can result in delayed onset of dysrhythmias, shock, sudden cardiac collapse, and bowel ischemia.

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