Calcium channel blocker toxicity

Background

• Hemodialysis is ineffective
• Precipitous deterioration is common (esp w/ verapamil)
• Nifedipine can kill a child with a single pill

2 Classes

Dihydropyridines

• Nifedipine, Amlodipine, Nicardipine
  • Systemic vasodilation, mild effect on heart
• Toxicity = Hypotension, reflex tachycardia
• With higher doses of toxicity peripheral selectivity is lost
  • I.e. may see decreased inotrophy, bradycardia

Non-dihydropyridines (verapamil, diltiazem)

• Stronger effect on heart, weak vasodilators
• Toxicity = Bradycardia, decreased inotropy

Clinical Features

• Cardiovascular
  • Hypotension (any CCB overdose)
  • Bradycardia (usually only seen with verapamil/diltiazem)
  • AV/sinus block
  • CHF
• Pulmonary
  • Respiratory depression
  • Pulmonary edema
• GI
  • Nausea/vomiting
• Neurologic
  • Lethargy, confusion, coma
• Metabolic
  • Hyperglycemia (due to insulin resistance)

Differential Diagnosis

• Beta blockers
  • More likely to cause CNS changes
  • Hypoglycemia is more common
• Digoxin
  • Nausea/vomiting is more common
• Clonidine
  • Miosis, somnolence
• Cholinergic agents
  • SLUDGE

Diagnostic Evaluation

• ECG
  • PR prolongation (varying degrees of AV block)
    • AV block occurs more commonly with verapamil
  • Bradydysrhythmia
• Glucose
• Chemistry
  • Serum calcium is often normal

Management

The majority of literature on calcium channel blocker overdose management is low-quality evidence and high-dose insulin and extracorporeal life support have the best evidence; other therapies such as include calcium, dopamine, norepinephrine, and lipid emulsion therapy may be beneficial but are poorly studied

• Monotherapy only successful for trivial overdoses

Charcoal

• 1g/kg (max 50g) x1
  • Consider if present w/in 1-2hr w/ delayed-release preparation

High-dose insulin and glucose

• Takes 30-60min for effect
• Glucose:
  • Adult: 50mL of D50W
  • Ped: 2.5mL/kg of D10
• Insulin bolus 1 unit/kg followed by 0.5units/kg/hr
  • Titrate infusion until hypotension is corrected or max 2u/kg/hr
  • Requires frequent glucose and K checks
• Potassium
  • If <3 administer 20mEq IV

Calcium

Avoid if digoxin toxicity is possible

• Calcium gluconate 3g (30-60mL of 10% soln)
• Calcium chloride 1-3g IV bolus (10-20mL of 10% soln (requires large IV/central line)
  • Preferred over calcium gluconate because it provides triple the amount of calcium on a weight-to-weight basis
  • Effects of calcium are transient
  • Repeat dosing often required
    • Alternatively, can be given as an infusion: 2-6g/hour

Vasopressors

• Norepinephrine is agent of choice

Glucagon

• 5mg IV bolus q10min x 2

Fluids

• Initial 20cc/kg bolus especially if source of hypotension is undifferentiated and also possibly hypovolemic or due to Sepsis

Atropine

• Adult: 0.5-1mg IV q2-3min to max of 3g
• Ped: 0.02mg/kg (minimum is 0.1mg)

Intravenous lipid emulsion

• 1.5mL/kg bolus of 20% lipid followed by 0.25mL/kg/minute

Disposition

• Admit all symptomatic pts
• Admit all sustained-release ingestions
• D/C if asymptomatic x 6-8hrs

See Also

• Calcium Channel Blockers