How does this medication work? What will it do for me?

Diltiazem belongs to a family of medications known as calcium channel blockers. It is used alone or with other medications to treat high blood pressure and angina (chest pain). It works by relaxing blood vessels and by reducing the workload of the heart. The injectable form of this medication is sometimes used in the hospital to bring abnormal heart rhythms under control.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

What form(s) does this medication come in?

ratio-Diltiazem CD is no longer being manufactured for sale in Canada. For brands that may still be available, search under diltiazem. This article is being kept available for reference purposes only. If you are using this medication, speak with your doctor or pharmacist for information about your treatment options.

How should I use this medication?

The recommended dose of diltiazem can range from 30 mg to 360 mg daily. The dose for the tablet form of diltiazem is usually taken 3 or 4 times a day. The dose for the capsule form of diltiazem is usually taken once daily. Swallow the capsules whole with fluids. Do not chew, or crush , or open the capsules.

The starting dose of diltiazem to treat angina is usually 120 mg to 180 mg daily. Depending on how well the medication is tolerated and how effective it is at this dose, your doctor may gradually increase the dose every 1 to 2 weeks to a maximum of 360 mg daily.

The starting dose to treat high blood pressure is usually 180 mg to 240 mg daily. It may take 2 to 4 weeks to reach a maximum benefit with any one dose, therefore dose increases should not be done more often than every 2 weeks, to a maximum of 360 mg daily.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

It is important to take this medication exactly as prescribed by your doctor. If you miss a dose, take it as soon as possible and continue on with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue on with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature, protect it from light and moisture, and keep it out of the sight and reach of children.

Do not dispose of medications in wastewater (e.g. down the sink or in the toilet) or in household garbage. Ask your pharmacist how to dispose of medications that are no longer needed or have expired.

Who should NOT take this medication?

Do not take diltiazem if you:

  • are allergic to diltiazem or any ingredients of the medication
  • are or may become pregnant
  • have certain types of heart rhythm problems in the absence of a pacemaker
  • have very low blood pressure
  • have weakened pumping action of the heart (called left ventricular failure)

What side effects are possible with this medication?

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

  • constipation
  • diarrhea
  • dizziness or lightheadedness
  • flushing
  • headache
  • heartburn
  • nausea
  • nervousness
  • tiredness or weakness

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not check with your doctor or seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

  • abdominal pain
  • breathing difficulty, coughing, or wheezing
  • fainting
  • irregular or fast, pounding heartbeat
  • skin rash
  • slow heartbeat (less than 50 beats per minute)
  • swelling of ankles, feet, or lower legs
  • vomiting

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Are there any other precautions or warnings for this medication?

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Blood pressure: Diltiazem may lower blood pressure too much in certain cases. If you experience lightheadedness, weakness, or dizziness, talk to your doctor.

Congestive heart failure: If you have congestive heart failure, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Diabetes: Diltiazem may cause an increase in blood sugar levels and glucose tolerance may change. People with diabetes may find it necessary to monitor their blood sugar more frequently while using this medication.

If you have diabetes or are at risk for developing diabetes, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Heart rhythm problems: In people with certain types of heart rhythm problems (sick sinus syndrome, second- and third-degree atrio-ventricular block) who do not have pacemakers, diltiazem may cause abnormally slow heart rates. People with certain types of heart rhythm problems should not take diltiazem. If you have a heart rhythm problem, your doctor should closely monitor your condition while you are taking diltiazem. Talk to your doctor if you have any concerns.

Kidney function: The kidneys are partially responsible for removing diltiazem from the body. As a result, kidney disease or reduced kidney function may cause this medication to build up in the body, causing side effects. If you have reduced kidney function or kidney disease, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Liver function: Liver disease or reduced liver function may cause this medication to build up in the body, causing side effects. If you have liver problems, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed. Your doctor may want to test your liver function regularly with blood tests while you are taking this medication.

Rarely, diltiazem may cause liver damage. If you experience symptoms of liver problems such as fatigue, feeling unwell, loss of appetite, nausea, yellowing of the skin or whites of the eyes, dark urine, pale stools, abdominal pain or swelling, and itchy skin, contact your doctor immediately.

Pregnancy: Women who are or may become pregnant should not take diltiazem. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: Diltiazem passes into breast milk. If you are a breast-feeding mother and are taking diltiazem, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of diltiazem for use by children have not been established.

What other drugs could interact with this medication?

There may be an interaction between diltiazem and any of the following:

  • aliskiren
  • alpha blockers (e.g., alfuzosin, doxazosin, silodosin, tamsulosin)
  • amiodarone
  • amphetamines (e.g., dextroamphetamine, lisdexamphetamine)
  • anaesthetics
  • angiotensin converting enzyme inhibitors (ACEIs; e.g., captopril, lisinopril, ramipril)
  • angiotensin receptor blockers (ARBs; e.g., candasartan, irbesartan, losartan)
  • anti-cancer medications (e.g., cabazitaxel, docetaxel; doxorubicin; etoposide, ifosfamide, irinotecan, vincristine)
  • aprepitant
  • aripiprazole
  • "azole" antifungals (e.g., fluconazole, ketoconazole, itraconazole)
  • barbiturates (e.g., butalbital, phenobarbital)
  • benzodiazepines (e.g., chlordiazepoxide, clonazepam, diazepam, lorazepam)
  • beta-adrenergic blocking agents (e.g., atenolol, labetalol, metoprolol)
  • bocepravir
  • bosutinib
  • buprenorphine
  • buspirone
  • busulfan
  • calcitriol
  • calcium channel blockers (e.g., amlodipine, diltiazem, nifedipine, verapamil)
  • calcium supplements (e.g., calcium carbonate, calcium citrate)
  • carbamazepine
  • carvedilol
  • chloroquine
  • cimetidine
  • ciprofloxacin
  • clonidine
  • clopidogrel
  • conivaptan
  • oral corticosteroids (e.g., dexamethasone, hydrocortisone, prednisone)
  • cyclosporine
  • dabrafenib
  • dantrolene
  • dapsone
  • dasatinib
  • deferasirox
  • digoxin
  • disopyramide
  • diuretics (water pills; e.g., furosemide, hydrochlorothiazide, triamterene)
  • erlotinib
  • estrogens (e.g., conjugated estrogen, estradiol, ethinyl estradiol)
  • ethosuximide
  • everolimus
  • felbamate
  • flecainide
  • flutamide
  • "gliptin" diabetes medications (e.g., linagliptin, saxagliptin, sitagliptin)
  • grapefruit juice
  • guanfacine
  • haloperidol
  • HIV non-nucleoside reverse transcriptase inhibitors (NNRTIs; e.g., delaviridine, efavirenz, etravirine, nevirapine)
  • HIV protease inhibitors (e.g., atazanavir, indinavir, ritonavir, saquinavir)
  • imatinib
  • lidocaine
  • lithium
  • lomitapide
  • losartan
  • macrolide antibiotics (e.g., clarithromycin, erythromycin)
  • maraviroc
  • mefloquine
  • mestranol
  • methadone
  • methylphenidate
  • metronidazole
  • mifepristone
  • mirtazapine
  • modafinil
  • monoamine oxidase inhibitors (MAOIs; e.g., moclobemide, rasagiline, selegiline, tranylcypromine)
  • montelukast
  • nateglinide
  • nefazodone
  • nilotinib
  • nitrates (e.g., isosorbide dinitrate, isosorbide mononitrate)
  • ondansetron
  • oxcarbazepine
  • oxycodone
  • pazopanib
  • pentoxifylline
  • perampanel
  • phenytoin
  • phosphodiesterase 5 inhibitors (e.g., sildenafil, tadalafil, vardenafil)
  • pimozide
  • praziquantel
  • primaquine
  • primidone
  • procainamide
  • progestins (e.g., dienogest, levonorgestrel, medroxyprogesterone, norethindrone)
  • propafenone
  • proton pump inhibitors (e.g., lansoprazole, omeprazole)
  • quetiapine
  • quinidine
  • quinine
  • ranitidine
  • repaglinide
  • rifabutin
  • rifampin
  • rilpivirine
  • rituximab
  • rivaroxaban
  • romidepsin
  • selective serotonin reuptake inhibitors (SSRIs; e.g., citalopram, duloxetine, fluoxetine, paroxetine, sertraline)
  • sirolimus
  • "statin" anti-cholesterol medications (e.g., atorvastatin, lovastatin, simvastatin)
  • St. John's wort
  • tacrolimus
  • tamoxifen
  • temsirolimus
  • teniposide
  • tetracycline
  • theophylline
  • ticagrelor
  • ticlopidine
  • tolterodine
  • tolvaptan
  • trabectedin
  • tramadol
  • trazodone
  • tricyclic antidepressasnts (e.g., amitriptyline, clomipramine, desipramine, trimipramine)
  • trimethoprim
  • ulipristal
  • venlafaxine
  • warfarin
  • zolpidem
  • zonisamide
  • zopiclone

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

  • stop taking one of the medications,
  • change one of the medications to another,
  • change how you are taking one or both of the medications, or
  • leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications that you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.