Diltiazem

What is this medication for?

• Supraventricular tachyarrhythmias, atrial fibrillation (rate control, adjunct to digoxin), pulmonary high blood pressure (adjunct)
• Hypertrophic cardiomyopathy (one of the drugs of choice), SVT

How is it given?

Give exactly as your veterinarian prescribed — never change the dose or stop on your own unless your veterinarian has told you to.

What if I miss a dose?

• Give it as soon as you remember — unless it is almost time for the next dose (then skip the missed one; never double up).
• Call your clinic if you miss more than one dose in a row.

Side effects — what should I watch for?

Effects listed as common in this handout

• Bradycardia (Most prominent)
• Vomiting, loss of appetite, stomach/intestinal distress (Most common)
• Hypotension, myocardial depression, AV block (Dose-related)
• Lethargy, weight loss (with 60 mg SR pellet dose) (~36% of cats in one study)

Worth a phone call to your veterinarian

• Any new symptom that worries you.

⚠️ Contact your veterinarian or an emergency clinic IMMEDIATELY if you notice

• Trouble breathing, collapse, seizures, severe vomiting or diarrhea, facial swelling, or pale gums

Before starting (or refilling), tell your veterinarian if your pet:

• has or has had: Severe low blood pressure (<90 mmHg systolic), sick sinus syndrome, 2nd/3rd-degree AV block (without pacemaker), acute MI, radiographic pulmonary congestion
• has or has had: Geriatric patients, heart failure (especially with concurrent beta-blockers), hepatic/renal impairment; give into a vein push over ≥2 min

• is pregnant, nursing, or used for breeding
• is taking any other medications, supplements, or flea/tick products, including:
  • Beta-blockers
  • Cyclosporine
  • Digoxin
  • Cimetidine
  • Quinidine
  • Do not mix into a vein solution with furosemide

Storage and handling

Room temperature, protect from light. Compounded oral formulations stable 50–60 days; transdermal compounding unreliable (ineffective in cats per Papich).

Good to know

• Extended-release ("XR"/"SR"/"CD") formulations are difficult to dose accurately in cats — inconsistent plasma levels can mean ineffective treatment in some cats and toxicity in others; if using SR, stick to specifically studied products/doses (e.g., Dilacor XR 30 mg/cat).
• Preferred over verapamil in heart failure patients due to less myocardial depression.
• In dogs with atrial fibrillation, combining with digoxin gives greater rate control than either drug alone.