Calcium channel blockers, commonly used to treat hypertension and cardiac dysrhythmias, have a significant risk of toxicity if used inappropriately. 

• As with most poisonings, prehospital management options are limited.  Protect the airway, ensure optimal oxygenation, support ventilation as necessary, and attempt to correct hypotension.  Care more generally for the patient than for the specific suspected poison.
• Hypotension and bradycardia are common findings.
• Be aware of the possibility of co-ingestion of other medications or substances.
• Pre-existing heart disease and myocardial ischemia can cause symptoms similar to calcium channel blocker overdose, and must be excluded.

• As a first line treatment, a fluid bolus of 500 mL should be given to any patient suspected of having overdosed on calcium channel blockers who is hypotensive, and may be repeated as necessary up to 1 L.
• Atropine should be considered in patients who are bradycardic, repeated as necessary, up to a total dose of 3 mg.
• Intravenous calcium (either calcium chloride or calcium gluconate) may overcome the cardiovascular effects of calcium channel blockers.  100 to 200 mg can be given intravenously, ideally over at least 10 minutes. 

• Calcium channel blockers can be divided into two categories: the dihydropyridines, which block L-type calcium channels in the vasculature, and the non-dihydropyridines, which act on calcium channels in the myocardium.
  • The dihydropyridines include nifedipine, amlodipine, and felodipine.  They are potent vasodilators, and have limited effect on cardiac contractility or conduction.  The non-dihydropyridines, diltiazem and verapamil, and act more centrally.
• In general, dihydropyridine drugs are more likely to cause aterial vasodilation and tachycardia, whereas dilitazem and verapamil tend to produce bradycardia and poor contractility.
• The changes in myocardial contractility may induce symptoms of heart failure.  Carefully evaluate patients for signs of myocardial dysfunction, including shortness of breath and pulmonary edema. 
• Patients who have overdosed on calcium channel blockers may have a significant hyperglycemia.  This is clinically insignificant, but may assist in diagnosis.  Obtain and record a capillary blood glucose measurement.
• Epinephrine infusions may be required for patients whose hypotension and bradycardia are refractory to atropine and calcium. Profound calcium channel blocker toxicity may require significantly higher doses and dose rates than might otherwise be expected.  Titrate drug doses to effect; be aware of arrhythmogenic potential.

Poisoning/Overdose

1. Barrueto F. Calcium channel blocker poisoning. In UpToDate. 2020. [Link]