Diltiazem HCl

By Rania Gollakner, BS, DVM, MPH

What is diltiazem?

Diltiazem (brand names: Cardizem®, Dilacor XR®, Tiazac®, Diltia XT®, Taztia XT®, Dilt-XR®) is a calcium channel blocker antiarrhythmic used in cats, dogs, and ferrets to treat certain heart and vascular conditions such as supraventricular tachycardias due to atrial fibrillation, pulmonary hypertension, systemic hypertension, or hypertrophic cardiomyopathy.

Its use in cats, dogs, and ferrets to treat heart conditions is ‘off label’ or ‘extra label’. Many drugs are commonly prescribed for off label use in veterinary medicine. In these instances, follow your veterinarian’s directions and cautions very carefully as their direction may be significantly different from those on the label.

How is diltiazem given?

This medication is given by mouth in the form of a tablet or capsule. It can be given with or without food, but if your pet vomits after receiving the medication on an empty stomach, try giving future doses with a meal or a treat. Some tablets and capsules must be given whole to work properly, follow directions carefully.

Diltiazem may also be compounded into a liquid form to be given by mouth. Follow the directions on the label and measure doses carefully.

Diltiazem can also be given by injection into the vein in the hospital setting.

This medication should take effect within 1 to 2 hours; however, effects may not be visibly noticeable and therefore laboratory tests may need to be done to evaluate this medication’s effectiveness.

What if I miss giving my pet the medication?

Give the missed dose as soon as you remember, and then wait the recommended amount of time between doses. Never give your pet two doses at once or give extra doses.

Are there any potential side effects?

The most common side effect in dogs is a slow heart rate. In cats, the most common side effect is vomiting. Side effects that may occur in cats or dogs can include lethargy, decreased appetite, weight loss, or general stomach upset.

More severe side effects such as low blood pressure, abnormal heart rhythms, neurological effects, and elevated liver enzymes may occur. Signs of these severe side effects may include collapse, severe weakness, yellowing of the skin, eyes and gums, and skin rashes.

This short-acting medication should stop working within 24 hours, although effects can be longer in pets with liver or kidney disease.

Are there any risk factors for this medication?

Diltiazem should not be used in pets that are allergic to it or that have severely low blood pressure, abnormal heart rhythms such as sick sinus syndrome or AV block, acute myocardial infarction, or X-ray evidence of lung congestion. It should be used cautiously in pets that are geriatric or pets that have heart failure, liver or kidney disease, or are receiving beta blockers. Diltiazem should be used with extreme caution in pregnant or lactating animals; the benefits of using this medication during pregnancy and lactation should outweigh the risks.

Are there any drug interactions I should be aware of?

The following medications should be used with caution when given with diltiazem: amiodarone, general anesthetics, benzodiazepines, beta-blockers, buspirone, clopidogrel, cimetidine/ranitidine, cyclosporine, digoxin, macrolide antibiotics, fentanyl, fluconazole/ketoconazole, hydrocodone, methylprednisolone, morphine, phenytoin, quinidine, rifampin, tacrolimus, theophylline, and vincristine.

Be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking.

Is there any monitoring that needs to be done with this medication?

Certain monitoring will be done while your pet is using this medication including electrocardiogram (ECG), heart rate, and blood pressure. Your veterinarian will schedule these appointments at the appropriate intervals for your pet. Monitor for severe side effects. Your veterinarian will monitor your pet to be sure that the medication is working.

How do I store diltiazem?

This tablets and capsules should be stored at room temperature in a tight container and protected from light. For liquid compounded forms, follow the directions on the label.

What should I do in case of emergency?

If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility and contact an animal poison control center.

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