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Diltiazem (Cardizem, Tiazac)

Non-dihydropyridine calcium channel blocker

Mechanism of action

Blocks L-type calcium channels in both vascular smooth muscle AND cardiac tissue (SA node, AV node, myocardium). The result: lowered BP, slowed AV conduction, and reduced contractility. Used for rate control in atrial fibrillation/flutter, supraventricular tachycardia, hypertension, and angina.

Adverse effects

Life-threatening / NCLEX-tested

  • Severe bradycardia and AV block — life-threatening with IV use
  • Worsening of heart failure (reduced contractility — avoid in HFrEF)
  • Hypotension, especially with rapid IV push
  • Profound bradycardia/asystole when combined with IV beta blockers
  • Hepatotoxicity (rare)

Side effects

Common — what to teach

  • Constipation (very common — fiber and fluids)
  • Headache
  • Dizziness
  • Peripheral edema (less than amlodipine)
  • Flushing
  • Gingival hyperplasia

Food & drug interactions

Combined with beta blockers, amplifies bradycardia and AV block — combined IV use is generally avoided. Digoxin levels rise — monitor. Statins (especially simvastatin and lovastatin) reach toxic levels via CYP3A4 inhibition; cap simvastatin at 10 mg. Grapefruit juice raises levels. Combine with care in HF — verapamil/diltiazem reduce contractility.

Nursing implications

Assessment, monitoring, patient teaching

  • Check apical pulse and BP before every dose; hold for HR < 60 or SBP < 100 unless ordered otherwise
  • For IV use during a-fib rate control, monitor continuous ECG and have BP cuff ready — drop is fast
  • Counsel patients about constipation prevention from day 1 (fiber, fluids, ambulation)
  • Avoid concurrent IV beta blocker without explicit physician direction
  • Teach to avoid grapefruit
  • If patient is on digoxin, reinforce monitoring for bradycardia and digoxin levels

When to hold / contraindications

  • HR < 60 bpm
  • SBP < 90–100 mmHg
  • Second- or third-degree AV block (without pacemaker)
  • Acute decompensated heart failure with reduced ejection fraction
  • Sick sinus syndrome (without pacemaker)

Memory anchor

Non-DHP CCBs (diltiazem, verapamil) act on the heart — slow it down. "Diltiazem drops the rate." Don't combine IV diltiazem with IV beta blocker; expect constipation.

Reminder: Drug cards are study aids, not clinical guidance. Always cross-check doses, holds, and contraindications with your facility's formulary and your clinical instructors before patient care.

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