Diltiazem
Diltiazem is a nondihydropyridine calcium-channel blocker with prominent effects on cardiac conduction and rate. It is used mainly for ventricular rate control in supraventricular tachyarrhythmias in dogs and cats. Additional specialist applications include selected feline cardiomyopathy cases in which heart-rate reduction or improved diastolic filling is a treatment goal.
Group
Non-dihydropyridine calcium-channel blocker
Mechanism of Action
Diltiazem blocks L-type calcium channels in cardiac nodal tissue, myocardium and vascular smooth muscle. Reduced calcium entry slows conduction through the atrioventricular node and increases nodal refractoriness, reducing ventricular response to rapid atrial activity. It also slows sinoatrial activity, reduces myocardial contractility and relaxes vascular smooth muscle. Reduced heart rate can lengthen diastolic filling time.
Dose Rates
Dog
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Supraventricular rate control | 0.5–1.5 mg/kg | PO | Every 8 h | |
| Atrial fibrillation | 5 mg/kg | PO | Every 12 h | High-dose monotherapy alternative, titrated clinically. |
| Atrial fibrillation combination | Reference only | PO | Diltiazem 3 mg/kg every 12 hours with digoxin 0.005 mg/kg every 12 hours. | |
| Atrial fibrillation | 0.05–0.25 mg/kg | IV | Every 0.0833333333 h | Titrate to effect with continuous monitoring. |
| Supraventricular tachycardia | 0.25 mg/kg | IV | Inject over 2 minutes, assess for 20 minutes before considering repeat. | |
| Supraventricular tachycardia infusion — Loading | 0.15–0.25 mg/kg | IV | Over 2 minutes. | |
| Supraventricular tachycardia infusion — Maintenance | 0.1–0.2 mg/kg/hour | IV | Continuous | Titrate; source maximum infusion rate is 0.4 mg/kg/hour. |
| Renal perfusion support — Loading | 0.2 mg/kg | IV | Historical/experimental acute renal failure use; inject slowly. | |
| Renal perfusion support — Maintenance | 3–5 mcg/kg/min | IV | Continuous | Historical/experimental regimen. |
| Pulmonary hypertension adjunct | 1–2 mg/kg | PO | Every 8 h | |
| Emergency hypertension | 0.5 mg/kg | PO | Every 6 h | Alternative when nitroprusside monitoring facilities are unavailable; monitor blood pressure and cardiac conduction. |
| Acute supraventricular tachycardia | Reference only | IV | Alternative protocol: 0.05 mg/kg over 1–2 minutes, repeat at five-minute intervals up to twice. Another uses 0.25 mg/kg over five minutes. Continuous ECG and blood-pressure monitoring are required. | |
| Emergency supraventricular tachyarrhythmia | Reference only | IV | 0.25 mg/kg over two minutes; additional 0.25 mg/kg doses every 15 minutes until conversion or a cumulative total of 0.75 mg/kg. The cumulative per-kg cap requires a protocol calculator. | |
| Chronic supraventricular tachycardia titration | Reference only | PO | Begin 1 mg/kg every 8 hours and titrate to a maximum 4 mg/kg every 8 hours. The 2–4 mg/kg doses should not be used with moderate or severe myocardial failure or substantial cardiac compromise. |
Cat
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Cardiac rate control | 1.75–2.4 mg/kg | PO | Every 8 h | Immediate-release formulation. |
| Cardiac rate control | 7.5–10 mg/animal | PO | Every 8 h | Alternative immediate-release fixed regimen; some patients are reduced to every 12 hours. |
| Extended-release cardiac rate control | 10 mg/kg | PO | Every 24 h | Dilacor XR/Cardizem CD; variable exposure and adverse effects limit routine use. Source fixed alternatives of 30 or 60 mg/cat lack a clearly repeated schedule; 30 mg caused fewer adverse effects. |
| Emergency hypertension | 0.5 mg/kg | PO | Every 6 h | Alternative when nitroprusside monitoring facilities are unavailable; monitor blood pressure and cardiac conduction. |
| Emergency supraventricular tachyarrhythmia | Reference only | IV | 0.25 mg/kg over two minutes; additional 0.25 mg/kg doses every 15 minutes until conversion or a cumulative total of 0.75 mg/kg. The cumulative per-kg cap requires a protocol calculator. |
Horse
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Atrial fibrillation | Reference only | IV | 0.125 mg/kg over at least 2 minutes, repeated every 10 minutes if needed, to a cumulative 1.1 mg/kg. Repeated-dose cumulative cap requires protocol support. |
Ferret
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Hypertrophic cardiomyopathy | 2–7.5 mg/kg | PO | Every 12 h | Titrate to effect and monitor for AV block. |
Indications
- Ventricular rate control in dogs and cats with atrial fibrillation or atrial flutter.
- Treatment of selected supraventricular tachycardias involving atrioventricular nodal conduction.
- Specialist adjunctive management of selected cats with hypertrophic cardiomyopathy when rate reduction or diastolic filling support is indicated; outcome evidence is limited.
Contraindications
- Hypotension
- Avoid rapid IV injection.
Interactions
- Do not mix IV solution with furosemide.
- Digoxin and beta blockers increase conduction-slowing effects.
Adverse effects
- Bradycardia, AV block, hypotension and myocardial depression
- Anorexia, vomiting and lethargy
Toxicity
Severe hypotension requires cardiovascular support and clinician-directed calcium therapy.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Diltiazem immediate-release 30 mg | Tablet | 30 mg / tablet | PO |
| Diltiazem immediate-release 60 mg | Tablet | 60 mg / tablet | PO |
| Diltiazem immediate-release 90 mg | Tablet | 90 mg / tablet | PO |
| Diltiazem immediate-release 120 mg | Tablet | 120 mg / tablet | PO |
| Diltiazem extended-release 120 mg Use only with an extended-release regimen; do not crush release-controlling units. | Capsule | 120 mg / capsule | PO |
| Diltiazem extended-release 180 mg Use only with an extended-release regimen; do not crush release-controlling units. | Capsule | 180 mg / capsule | PO |
| Diltiazem extended-release 240 mg Use only with an extended-release regimen; do not crush release-controlling units. | Capsule | 240 mg / capsule | PO |
| Diltiazem injection 5 mg/mL | Injection | 5 mg / mL | IV |
Monitoring and Administration
Monitor ECG, heart rate and blood pressure. Extended-release and immediate-release formulations are not interchangeable by schedule.
Extended-release exposure in cats may be inconsistent; do not crush release-controlling units. Only specifically confirmed multiparticulate products may be opened.
Diluted IV solution should be discarded after 24 hours; do not freeze.