Adenosine

• Mechanism of Action
  • Adenosine receptor agonist
• Clinical Indications
  • Stable AVNRT/AVRT
    • First dose
      • Adult: 6 mg IV
      • Peds: 0.1 mg/kg IV
    • Second dose
      • Adult: 12 mg IV
      • Peds: 0.2 mg/kg IV
• Cerebral
  • Minimal
• Cardiovascular
  • Transient conduction cessation at the SA and AV node
  • ↓ MAP
  • ↓ HR
  • ↓ CO
• Pulmonary
  • Bronchoconstriction
• Renal
  • Minimal
• Hepatic
  • Minimal
• Contraindications
  • Any rhythm that is not AVRT/AVNRT
  • WPW syndrome
  • Asthma
• Board Facts
  • Rapid injection following by a saline flush
  • Raise limb to facilitate adenosine movement into central circulation
  • If AVRT/AVNRT rhythm does not terminate after second dose of adenosine, consider monomorphic ventricular tachycardia
  • Methylxanthines antagonize adenosine requiring an increased dose
  • Carbamazepine and dipyridamole potentiate adenosine action and thus require a reduced dose [108]
  • Transplanted hearts/denervated hearts require a reduced dose [109]

Amiodarone

• Mechanism of Action
  • Na⁺, K⁺, and Ca²⁺ channel antagonist (Figure 4.12)
• Clinical Indications
  • VF/pulseless VT
    • First dose
      • Adult: 300 mg IV
      • Peds: 5 mg/kg IV
    • Second dose
      • Adult: 150 mg IV
      • Peds 2.5 mg/kg IV
  • Stable wide QRS tachycardia with a pulse
    • Adult: 150 mg IV over 10 minutes
    • Peds: 5 mg/kg IV over 20–60 minutes
  • Atrial fibrillation
• Cerebral
  • Minimal
• Cardiovascular [110]
  • ↓ MAP
  • Minimal change in HR
  • ↑ CO
• Pulmonary
  • Pulmonary fibrosis (in chronic use)
• Renal
  • ↓ RBF [111]
  • Renal toxicity [112]
• Hepatic
  • Primary site of metabolism
  • Hepatic toxicity (primarily with chronic use) [113]
• Contraindications
  • Pregnancy
  • Renal pathology
  • Pulmonary pathology
  • Hepatic pathology
  • Thyroid pathology

• Board Facts
  • Chronic use may cause blue–gray skin discoloration and toxic toxicity [114, 115]
    • Amiodarone toxicity is mostly related to chronic oral, rarely occurs with acute administration

Atropine

• Mechanism of Action
  • Muscarinic receptor antagonist
• Clinical Indications
  • Bradycardia with a pulse
    • Adult: 0.5 mg IV (Max 3 mg)
    • Peds: 0.02 mg/kg IV (Max 1 mg)
    • Peds: 0.02 mg/kg IM
  • Coadministration with neuromuscular reversal
    • Neuromuscular reversal covered on page 138
• Cerebral
  • May present as excitation or sedation in high doses
• Cardiovascular
  • ↑ CO
  • ↑ HR
  • Low‐dose atropine may cause bradycardia [75]
• Pulmonary
  • Bronchodilator
  • ↓ Secretions and thicken them
• Renal
  • Minimal
• Hepatic
  • Primary site of metabolism
• Contraindications
  • Acute angle glaucoma
  • Cardiac transplantation due to denervation
    • Paradoxical bradycardia can occur [76]
• Board Facts
  • Crosses placenta and BBB

Diltiazem

• Mechanism of Action
  • Non‐dihydropyridine calcium channel antagonist (Figure 4.12)
• Clinical Indications
  • Stable atrial flutter
    • 5–10 mg IV; Titrate, Max 50 mg
      • 0.25 mg/kg initial; 0.35 mg/kg next
  • Stable atrial fibrillation
    • 5–10 mg IV; Titrate, Max 50 mg
      • 0.25 mg/kg initial; 0.35 mg/kg next
  • Stable AVNRT/AVRT
    • 5–10 mg IV; Titrate, Max 50 mg
      • 0.25 mg/kg initial; 0.35 mg/kg next
• Cerebral
  • ↑ CBF
• Cardiovascular
  • ↑ CO
  • ↓ HR
  • ↓ MAP
• Pulmonary
  • Minimal
• Renal
  • Minimal
• Hepatic
  • Primary site of metabolism
• Contraindications
  • WPW syndrome
  • Bradycardia
  • Cardiac conduction delays
• Board Facts
  • Gingival overgrowth is generally caused by chronic administration [116]
  • Diltiazem can increase blood digoxin levels [117]

Verapamil

• Mechanism of Action
  • Non‐dihydropyridine calcium channel antagonist (Figure 4.12)
• Clinical Indications
  • Stable atrial flutter
    • 2.5–5 mg IV; Titrate to max 20 mg
  • Stable AVNRT/AVRT
    • 2.5–5 mg IV; Titrate to max 20 mg
• Cerebral
  • ↑ CBF
• Cardiovascular [118]
  • ↓ CO
  • ↓ HR
  • ↓ MAP
• Pulmonary
  • Minimal
• Renal
  • Minimal
• Hepatic
  • ↑ HBF [119]
• Contraindications
  • WPW syndrome
  • Bradycardia
  • Cardiac conduction delays

• Board Facts
  • Gingival overgrowth is generally caused by chronic administration [120]
  • Inhibitor of P₄₅₀ system [121]

References

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