Class IA: Quinidine
A naturally occurring nucleoside and G-pro-tein with its own specific adenosine receptors; IV boluses of adenosine are indicated to rapidly terminate reentrant and theophylline-induced SVTs.
Mechanisms: Provides an evanescent (10 sec) calcium entry block and increases AV nodal refractory period; reduces action potentials and reduces automaticity.
Toxicities: Transient asystole, atrial fibrillation, hypotension, bronchospasm. All toxicities are potentiated by the antiplatelet agent, dipyri-damole, an adenosine uptake inhibitor. Higher doses are required for methylxanthine overdoses due to adenosine receptor blockade. Treatment of toxicity: Supportive.
Mechanism: Na, K, and Ca channel blocker. Pharmacology: An amide local anesthetic, with excellent mucosal absorption, d-isomer of quinine, the antimalarial from cinchona bark; rapidly absorbed orally; high volume of distribution and protein binding.
Toxicity: Prolonged QT interval and widened QRS complex, ventricular tachycardia, ventricular fibrillation, torsades, hypotension, seizures, noncardiogenic pulmonary edema, cinchonism. Treatment: Decontamination — no ipecac, oro-gastric lavage; IV fluids and vasoMech (a cardiac and peripheral Na channel blocker).
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