Mar Vista Animal Medical Center

3850 Grand View Blvd.
Los Angeles, CA 90066






30 MG, 60 MG, 90 MG, 120 MG,
120 MG, 180 MG, 240 MG
300 MG, 360 MG, 420 MG



Muscle contraction is governed by the flow of calcium through what are called "voltage-gated calcium channels." When these channels are blocked by drugs, less calcium can flow through the channels. This results in a weaker muscle contraction. Blood calcium levels are not altered by this blockade.

The voltage-gated calcium channels that one might wish to block are located in heart muscle and in blood vessels. In the case of blood vessels, the use of a calcium channel blocker would lead to less muscle tone in the blood vessel. This creates a more relaxed and therefore dilated blood vessel which, in turn, translates to lower blood pressure. The heart ends up with less resistance to pump against, meaning that the heart does not have to work as hard. In situations where the heart muscle might be overworked, this might lead to a more efficient and healthier heart.

Diltiazem also affects the electrical conduction of the heart such that electrical conduction is slowed. This means that the heart rate also slows, allowing for a longer filling time for the heart between pumps.



Diltiazem is most commonly used in the treatment of hypertrophic cardiomyopathy in the cat. In this condition, the heart muscle becomes stiff and inflexible plus the filling chambers of the heart become smaller. The muscle-bound heart cannot fill normally for these reasons and since it cannot fill normally, it sends forth less blood with each pump. To meet the oxygen demands of the body, the diseased heart must pump faster than normal since it is pumping out less blood per pump. This over-works the heart and can lead to muscle fatigue and heart failure. By using a calcium channel blocker such as diltiazem, the heart relaxes and slows and thus may fill more efficiently. Better heart chamber filling means more blood output, no need to pump faster and less heart muscle fatigue.

By using a calcium channel blocker such as diltiazem, the heart may fill more efficiently.

Diltiazem might also be used in the treatment of high blood pressure (hypertension), should it arise from any of numerous situations.

Diltiazem can be given with or without food.

Diltiazem is typically given 2-3 times daily. Be sure you understand your pet's instructions.

Extended relief capsules have special time releasing beads. These should not be crushed.

If a dose of diltiazem is accidentally skipped, do not double up on the next dose. Simply give the next dose as would normally be scheduled.



The most common side effects are vomiting (generally mitigated by giving the medication with food). Weight loss may occur after 2-6 months.

Side effects of serious significance include: collapse (if heart rate and/or blood pressure drops too low), weakness, jaundice, skin rashes. These reactions necessitate intervention.



Diltiazem should not be used with beta-blockers (heart medications which might compound the low blood pressure side effect) such as atenolol or propranolol. Even beta-blocker eyedrops as might be used in glaucoma treatment could create adverse blood pressure reactions.

Cimetidine (an antacid) may increase the blood levels of diltiazem (making the effects of diltiazem stronger). Ranitidine, another antacid, also has this effect but not as strongly.

Medications that are stronger when used with diltiazem include: fentanyl, hydrocodone, vincristine, benzodiazepine tranquilizers (such as diazepam and alprazolam) and cyclosporine (an immunomodulator used to treat immune-mediated disease as well as allergy).

Medications that are weaker when used with diltiazem include: buspirone (an anti-anxiety medication).

Concurrent use of diltiazem with cisapride (a bowel motility modifier most commonly used for the treatment of obstipation/severe constipation) could lead to cardiac arrhythmia (disturbances in the electrical conduction of the heart).

Clopidogrel, a blood thinner, may not work as well in the presence of diltiazem.

Theophylline, an airway dilator, may have more potential for toxicity when used concurrently with diltiazem.

Concurrent use of diltiazem with macrolide class antibiotics (erythromycin, clarithromycin, azithromycin) may increase the toxicity of diltiazem.



  • Diltiazem should not be used in conditions where reduced strength of heart contraction or further slowing the heart rate could be dangerous. Such situations might include congestive heart failure, AV blockade-type heart arrhythmias, or low blood pressure.
  • Diltiazem should be avoided in patients with liver impairment or kidney failure. If use cannot be avoided, dose changes will likely be needed.
  • Diltiazem should not be used in pregnancy.
  • Diltiazem should be stored at room temperature and protected from light.


 Page posted: 12/22/2010
Page last updated: 3/19/2023