Can a patient be on both amlodipine and Cardizem (diltiazem)?

Concurrent Use of Amlodipine and Diltiazem

Concurrent use of amlodipine and diltiazem is generally not recommended due to the increased risk of additive hypotension, bradycardia, and conduction disturbances that could lead to significant cardiovascular complications. 1

Pharmacological Considerations

Mechanism and Interactions

Both medications are calcium channel blockers (CCBs) but work through different mechanisms:

• Amlodipine: A dihydropyridine CCB that primarily affects peripheral vasculature with minimal cardiac effects 1
• Diltiazem: A non-dihydropyridine CCB that significantly affects cardiac conduction and contractility 1

When used together, these medications can cause:

• Excessive hypotension
• Bradycardia
• Heart block
• Cardiac conduction abnormalities

Evidence of Interaction Risks

Research has shown that diltiazem is a moderate inhibitor of CYP3A4, which can affect the metabolism of amlodipine (a CYP3A4 substrate), potentially increasing amlodipine concentrations and side effects 1. Additionally, the combined negative chronotropic and dromotropic effects can be dangerous, particularly in:

• Patients with pre-existing conduction abnormalities
• Those with left ventricular dysfunction
• Elderly patients
• Patients with renal impairment 2

Clinical Decision Algorithm

When to Absolutely Avoid Combination

• Patients with:
  • Pre-existing bradycardia
  • AV block (any degree)
  • Sick sinus syndrome
  • Heart failure with reduced ejection fraction (HFrEF) 1
  • Hypotension

Alternative Approaches

If additional antihypertensive therapy is needed beyond a single CCB:

1. Preferred approach: Choose a medication from a different class:

   • ACE inhibitor or ARB
   • Thiazide diuretic
   • Beta-blocker (if indicated for compelling conditions like CAD)

2. If CCB therapy must be optimized:

   • Choose either amlodipine OR diltiazem at an optimal dose, not both
   • For vasospastic angina: Prefer amlodipine (5-10mg daily) 1
   • For rate control plus hypertension: Prefer diltiazem (120-360mg daily) 1

Monitoring Requirements

If, despite these recommendations, both medications must be used concurrently (which should be extremely rare):

• Monitor blood pressure and heart rate frequently
• Obtain baseline ECG and repeat regularly to assess for conduction abnormalities
• Start with lowest possible doses of both medications
• Watch for signs of hypotension (dizziness, syncope)
• Monitor for peripheral edema, which may be exacerbated with dual therapy 3, 4

Comparative Efficacy

When choosing between these agents individually:

• Amlodipine has been shown to produce greater reductions in systolic blood pressure compared to diltiazem for similar reductions in diastolic pressure 4, 5
• Amlodipine can be dosed once daily (2.5-10mg), while diltiazem often requires multiple daily dosing unless using extended-release formulations 1
• Both medications can reduce left ventricular mass in hypertensive patients, though through slightly different mechanisms 5

Conclusion

The concurrent use of amlodipine and diltiazem should generally be avoided due to the significant risk of additive cardiovascular effects that could lead to serious adverse outcomes including severe bradycardia, heart block, and hypotension. Alternative strategies using a single CCB with medications from other antihypertensive classes are strongly preferred for optimizing blood pressure control.