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What is diltiazem?

Diltiazem is a non-dihydropyridine calcium channel blocker. It works directly on the part of the heart that generates electrical signals, slowing their conduction and reducing the force of heart muscle contractions. This lowers the heart’s demand for oxygen and means it doesn’t have to work as hard.¹

Slowing the heart rate is particularly helpful for treating conditions in which the heart is beating too fast.

The drug also relaxes the coronary arteries, allowing blood to flow more easily and reducing blood pressure.²

What is diltiazem used to treat?

The oral form of diltiazem has been approved by the US Food and Drug Administration (FDA) for the treatment of hypertension and to improve exercise tolerance in angina. The intravenous form is approved for the control of rapid heart rhythms, also known as tachydysrhythmias.³ ⁴

Hypertension (high blood pressure) tends to develop over time in people with the condition, usually without causing symptoms until later in its course. Controlling high blood pressure is important because it leads to heart, brain, kidney, and blood vessel damage. This can increase your risk for serious problems like heart attack, stroke, and kidney failure. Diltiazem works to reduce blood pressure by relaxing the blood vessels.⁵

Diltiazem can also treat chest pain (angina). It works by expanding the arteries around the heart, which minimizes spasms in these blood vessels that can cause pain. Chest pain is often related to exertion, which increases the heart’s oxygen needs. Diltiazem helps with this condition by reducing the work of the heart muscle and increasing the flow of blood and oxygen to the heart.⁶

In its injectable formulation, diltiazem is used to control rapid abnormal heart rhythms, such as atrial fibrillation, atrial flutter, and paroxysmal supraventricular tachycardia. If left untreated, these rhythms can lead to severe complications, including weakening of the heart muscle, heart attack, stroke, and heart failure.⁷ 

Dosage forms and strengths

Your doctor might prescribe diltiazem in the form of regular or extended-release tablets or capsules. The injectable formulation is given by medical professionals in a healthcare setting.

Here are the available formulations:

Tablets (generic, Cardizem): 30mg, 60mg, 90mg, 120mg⁸ ⁹

Extended-release tablets (generic, Cardizem LA, Matzim LA): 120mg, 180mg, 240mg, 300mg, 360mg, 420mg¹⁰ ¹¹

Extended-release capsules:

  • 12-hour (generic): 60mg, 90mg, 120mg¹²

  • 24-hour (generic, Cardizem CD, Cartia XT, Taztia XT, Tiadylt ER, Tiazac ER): 120mg, 180mg, 240mg, 300mg, 360mg, 420mg¹³ ¹⁴ ¹⁵ ¹⁶ ¹⁷ ¹⁸

Injection (generic): 25mg/5mL, 50mg/10mL vials¹⁹

How do you take diltiazem?

Diltiazem is available in the form of standard tablets and extended-release tablets and capsules. You can take the tablets with or without food. Do not chew or crush the tablets, especially if you take the extended-release version.

Most people start by taking a low dose of diltiazem. Your doctor will typically increase your dose of the immediate-release tablets after several days or the extended-release tablets after 1–2 weeks.  

Regardless of your dosing schedule, it’s important to follow your doctor’s instructions for taking diltiazem exactly.

Seeing results from diltiazem

Diltiazem starts to affect your blood vessels from the first day you take the medication, but you might not see changes in your blood pressure readings for a few weeks.

The onset of action of immediate-release diltiazem tablets is 30–60 minutes. Peak plasma concentration levels are reached in 2–4 hours after administration.²⁰ ²¹

Detectable plasma levels are seen within 2–3 hours of taking the 12-hour extended-release capsule. Peak plasma levels are reached within 6–11 hours.²²

Controlled diltiazem absorption starts within one hour of taking a 24-hour extended-release capsule. The antihypertensive effects seen with this formulation peak 4–6 hours after administration. After 24 hours, the response is >50% of the peak response.²³ ²⁴ ²⁵

Who should not take diltiazem?

You should not take this drug if you have any of the following:²⁶ ²⁷ ²⁸

  • Sick sinus syndrome (without a functioning ventricular pacemaker)

  • Second- or third-degree AV block (without a functioning ventricular pacemaker)

  • Low blood pressure (less than 90mm Hg systolic)

  • A history of hypersensitivity to the drug

  • Acute myocardial infarction (heart attack) with pulmonary congestion

  • Wolff-Parkinson-White syndrome

Diltiazem should be used with caution in people with the following:²⁹

  • Very slow heart rates

  • Hypertrophic obstructive cardiomyopathy

  • Liver or kidney disease

  • Left ventricular dysfunction

  • Heart failure

Potential side effects

Diltiazem may cause side effects in some individuals. Some of the more common side effects include the following:³⁰

  • Headache

  • Swelling of the ankles and feet

  • Dizziness

  • Low blood pressure

  • Slowed heartbeat

  • Nausea, vomiting

  • Flushing

  • Muscle pain

  • Diarrhea

  • Constipation

  • Coughing

  • Nasal congestion

If any of these side effects persist or become more severe, talk to your doctor.

While uncommon, serious side effects have been reported with the use of diltiazem. If you experience any of the following, contact your doctor or the emergency services right away:³¹

  • Fainting

  • Severe fatigue

  • Swelling in your face or limbs

  • Yellowed skin or eyes

  • Worsening chest pain

  • Severe, peeling skin rash

  • Bleeding or bruising

  • Irregular heart rhythm or very slow heart rate

  • Difficulty breathing

Overdose

You can experience serious symptoms from taking too much diltiazem.

Overdoses can cause any of the following:³²

  • Slow heart rate

  • Low blood pressure

  • Fainting

  • Irregular heart rhythm

  • Dizziness

  • Trouble breathing

  • Nausea and vomiting

  • Heart failure

  • Cardiac arrest

Complications from taking too much diltiazem can become life-threatening, but they are usually treatable if you seek immediate medical attention.

Allergy information

Allergic reactions to diltiazem are rare, but they can happen. If you experience any of these signs of a serious allergic reaction, call 911 or go to the emergency department immediately:

  • Itchy, red, swollen, blistered, or peeling skin

  • Swelling of your mouth, tongue, or throat

  • Vomiting

  • Tightness in your chest

  • Wheezing, difficulty breathing

  • Rapid heart rate

  • Loss of consciousness

Long-term use of diltiazem

High blood pressure is a chronic condition, and people who take diltiazem for hypertension often need to continue taking it for several years or indefinitely.

Research published around the same time as the FDA approved the drug indicates that diltiazem is safe for long-term use.³³

Since then, studies have raised concerns about calcium channel blockers increasing risk of breast cancer. However, not all studies have observed an increased risk.³⁴

Pregnancy category

Diltiazem has been designated a pregnancy category C medication by the FDA, which means that animal studies have shown fetal adverse effects. However, the doses given were many times higher than those recommended for humans.³⁵

There haven’t been enough well-controlled studies carried out in humans during pregnancy to accurately determine the risks.³⁶

Diltiazem and pregnancy

The drug can increase the risk of complications during pregnancy, so you will need to talk to your doctor to weigh the individual risks and benefits in your case and determine alternative therapies if necessary.

Diltiazem and breastfeeding

Diltiazem passes into breast milk in small amounts, which are unlikely to cause any negative effects for breastfed infants. The risks and benefits of taking diltiazem while breastfeeding should be discussed with your doctor.³⁷

Missed doses

If you miss a dose of diltiazem, take it as soon as you remember unless it’s almost time to take your next dose. In that case, skip your missed dose and take the next dose at your regularly scheduled time. Don’t take extra diltiazem to make up for the missed dose.

Drug interactions

Numerous drugs are known to interact with diltiazem. Many of these are other medications prescribed with a similar goal, like lowering blood pressure or treating heart problems. They include the following:³⁸

  • Anesthetics

  • Antibiotics like rifampin, nafcillin, and rifapentine (Priftin)

  • Antidepressants:

  • Monoamine oxidase inhibitors (MAOIs), such as isocarboxazid (Marplan)

  • Buspirone

  • Antipsychotics, such as thioridazine and aripiprazole lauroxil (Aristada)

  • Benzodiazepines, such as alprazolam (Xanax), midazolam (Versed), and triazolam (Halcion)

  • Blood pressure medications:

  • Beta-blockers, like labetalol (Trandate)

  • Other calcium channel blockers, like felodipine, amlodipine (Norvasc), and nicardipine

  • Amiodarone

  • Blood thinners like rivaroxaban (Xarelto)

  • Cancer drugs like enzalutamide (Xtandi), apalutamide (Erleada), mitotane (Lysoderen), and midostaurin (Rydapt)

  • Cholesterol-lowering drugs like simvastatin (Zocor) and lovastatin (Altoprev)

  • Heart rhythm drugs like disopyramide (Norpace)

  • HIV drugs, such as etravirine (Intelence) and efavirenz

  • Seizure medications, such as phenytoin (Dilantin), carbamazepine (Tegretol), primidone (Mysoline), and others

  • Migraine drugs like ergotamine (Cafergot) and dihydroergotamine (DHE 45)

  • Colchicine (Colcrys)

  • Gastrointestinal medications like cimetidine (Tagamet HB 200), aprepitant (Emend), ozanimod (Zeposia), and naloxegol (Movantik)

  • Pain medications like oxycodone (Oxycontin), meperidine (Demerol), oliceridine (Olinvyk), and tramadol

  • Multiple sclerosis drugs, such as ponesimod (Ponvory)   

Is it safe to drink alcohol while taking diltiazem?

Controlled-release versions of diltiazem, like Cardizem CD, can release more quickly when taken with alcohol. This increases the risk of adverse effects, so it is recommended to avoid drinking alcohol while taking diltiazem in these forms.

What to discuss with your doctor

Before taking this drug, talk to your doctor about any concerns and risk factors. These might include:

  • Allergies: Tell your doctor if you are allergic to diltiazem, its ingredients, or any other calcium channel blockers.

  • Medications: Inform your doctor of all other prescription and over-the-counter drugs, vitamins, supplements, or herbal products you are currently taking, take occasionally, or plan to start taking. Some drugs can interact with diltiazem to cause adverse effects.

  • Medical conditions: Tell your doctor if you have any other medical conditions, including liver or kidney disease, low blood pressure, sinus node dysfunction (sick sinus syndrome), second- or third-degree AV block or other abnormal heart rhythms, and heart failure.

  • Pregnancy and breastfeeding: Tell your doctor if you are pregnant, planning a pregnancy, or breastfeeding.

Drug approval history

Here are some key dates in the approval history of diltiazem:

  • 1982: Diltiazem was first approved by the FDA to be sold under the brand name Cardizem — an immediate-release tablet. This is also now available as a generic medication.³⁹

  • 1997: The FDA approved a new formulation of diltiazem — a 12-hour, twice-daily, extended-release capsule.⁴⁰

  • 1991: Cardizem CD, a 24-hour extended-release capsule, was approved by the FDA. This is also now available as a generic medication in addition to other branded products.⁴¹

  • 2003: The FDA approved Cardizem LA, an extended-release tablet.⁴²

Tips for taking diltiazem

  • You can take diltiazem either with or without food, depending on what’s more comfortable and convenient for you.

  • If you’re taking an extended-release formulation of diltiazem, swallow the pills whole. Do not chew or crush them.

  • It is recommended to take your scheduled doses at approximately the same time each day.

  • Attend any follow-up appointments your doctor schedules after prescribing diltiazem. Your blood pressure needs to be monitored closely while you’re taking the drug.

  • If your doctor tells you to check your heart rate regularly, follow their instructions and contact your doctor right away if it’s slower than the target rate.

  • Follow any special dietary recommendations or other lifestyle changes your doctor has prescribed to improve your high blood pressure along with the medication. 

Frequently asked questions

What are the side effects of diltiazem?

The most common side effects are headaches, nausea, dizziness, swelling, low blood pressure, and rashes. More serious side effects can occur, but they are rare.

Does diltiazem lower your heart rate?

Diltiazem works directly on the areas of the heart that generate electrical signals and slows their conduction. This leads to a decreased heart rate. However, your heart rate should still remain within a healthy range.

Does diltiazem affect sleep?

Sleep disturbance is listed as a potential adverse effect on the drug label of verapamil, a similar medication. However, there is no data to indicate an association between diltiazem, verapamil, and this effect.⁴³

  1. Calcium Channel Blockers (2022) | NIH: StatPearls

  2. Calcium Antagonists Effects on Cardio-Renal Risk in Hypertensive Patients (2005)

  3. Label: DILTIAZEM HYDROCHLORIDE tablet DILTIAZEM HYDROCHLORIDE tablet (2023) | NIH: DailyMed

  4. Label: DILTIAZEM HYDROCHLORIDE injection (2022) | NIH: DailyMed

  5. Diltiazem | MedlinePlus

  6. Label: DILTIAZEM HYDROCHLORIDE tablet DILTIAZEM HYDROCHLORIDE tablet (2023) | NIH: DailyMed

  7. Label: DILTIAZEM HYDROCHLORIDE injection (2022) | NIH: DailyMed

  8. Label: DILTIAZEM HYDROCHLORIDE tablet DILTIAZEM HYDROCHLORIDE tablet (2023) | NIH: DailyMed

  9. Label: CARDIZEM- diltiazem hydrochloride tablet, coated (2020) | NIH: DailyMed

  10. Label: CARDIZEM LA- diltiazem hydrochloride tablet, extended release (2019) | NIH: DailyMed

  11. Label: MATZIM LA- diltiazem hydrochloride tablet, extended release (2021) | NIH: DailyMed

  12. Label: DILTIAZEM HYDROCHLORIDE EXTENDED-RELEASE- diltiazem hydrochloride capsule, extended release (2023) | NIH: DailyMed

  13. Label: DILTIAZEM HYDROCHLORIDE EXTENDED RELEASE- diltiazem hydrochloride capsule, extended release (2020) | NIH: DailyMed

  14. Label: CARDIZEM CD- diltiazem hydrochloride capsule, coated, extended release (2020) | NIH: DailyMed

  15. Label: CARTIA XT- diltiazem hydrochloride capsule, extended release (2020) | NIH: DailyMed

  16. "Label: TAZTIA XT- diltiazem hydrochloride capsule, extended release (2022) | NIH: DailyMed

  17. Label: TIADYLT ER- diltiazem hydrochloride capsule, extended release (2021) | NIH: DailyMed

  18. Label: TIAZAC EXTENDED RELEASE- diltiazem hydrochloride capsule, extended release (2020) | NIH: DailyMed

  19. Label: DILTIAZEM HYDROCHLORIDE injection (2022) | NIH: DailyMed

  20. Diltiazem | NIH: StatPearls

  21. Label: DILTIAZEM HYDROCHLORIDE tablet DILTIAZEM HYDROCHLORIDE tablet (2023) | NIH: DailyMed

  22. Label: DILTIAZEM HYDROCHLORIDE EXTENDED-RELEASE- diltiazem hydrochloride capsule, extended release (2023)  | NIH: DailyMed

  23. Label: DILTIAZEM HYDROCHLORIDE EXTENDED RELEASE- diltiazem hydrochloride capsule, extended release (2020) | NIH: DailyMed

  24. Label: DILTIAZEM HYDROCHLORIDE capsule, extended release (2022)| NIH: DailyMed

  25. (As above)

  26. Label: DILTIAZEM HYDROCHLORIDE tablet DILTIAZEM HYDROCHLORIDE tablet (2023) | NIH: DailyMed

  27. Cardizem, Cardizem CD (diltiazem) dosing, indications, interactions, adverse effects, and more | NIH: Reference Medscape

  28. Diltiazem | NIH: StatPearls

  29. Cardizem, Cardizem CD (diltiazem) dosing, indications, interactions, adverse effects, and more | NIH: Reference Medscape

  30. (As above)

  31. (As above)

  32. Label: DILTIAZEM HYDROCHLORIDE tablet DILTIAZEM HYDROCHLORIDE tablet (2023) | NIH: DailyMed

  33. Effects of long-term administration of diltiazem hydrochloride in hypertensive patients (1983)

  34. Calcium Channel Blocker Use and the Risk for Breast Cancer: A Population-Based Nested Case-Control Study (2022)

  35. CARDIZEM® (diltiazem hydrochloride) Direct Compression Tablets (2014)

  36. Drugs in pregnancy: Implications for a cardiologist (2010)

  37. Diltiazem | NIH: Drugs and Lactation Database (LactMed®)

  38. Label: DILTIAZEM HYDROCHLORIDE tablet DILTIAZEM HYDROCHLORIDE tablet (2023) | NIH: DailyMed

  39. Drug approval package (Cardizem) | US Food and Drug Administration

  40. Drug approval package (diltiazem extended-release capsule) | US Food and Drug Administration

  41. Drug approval package (Cardizem CD) | US Food and Drug Administration

  42. Drug approval package (Cardizem LA) | US Food and Drug Administration

  43. CV Drugs That Negatively Affect Sleep Quality (2013)

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Disclaimer

Here at HealthMatch, we’ve done our best to ensure that the information provided in this article is helpful, up to date, and, most importantly, accurate.

However, we can’t replace the one-to-one advice of a qualified medical practitioner or outline all of the possible risks associated with this particular drug and your circumstances.

It is therefore important for you to note that the information contained in this article does not constitute professional medical or healthcare advice, diagnosis or recommendation of treatment and is not intended to, nor should be used to, replace professional medical advice. This article may not always be up to date and is not exhaustive of all of the risks and considerations relevant to this particular drug. In no circumstances should this article be relied upon without independent consideration and confirmation by a qualified medical practitioner.

Your doctor will be able to explain all possible uses, dosages, precautions, interactions with other drugs, and other potential adverse effects, and you should always talk to them about any kind of medication you are taking, thinking about taking or wanting to stop taking.

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