Module 27.3 - Antihypertensive Toxicology - Lecture

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Welcome to this critical educational module on Antihypertensive Toxicology, designed to cultivate a profound understanding of these essential medications and their associated toxicologic considerations.
We begin by exploring the historical evolution of pharmacotherapy for hypertension, from first-generation agents developed in the 1960s—including centrally acting sympatholytics, direct vasodilators, and diuretics—to newer classes like ACEIs, ARBs, and DRIs.
The general principle of toxicity dictates that most antihypertensive overdoses manifest as an exaggeration of pharmacological effects, primarily driven by the degree of hypotension produced.
However, specialized management is required for certain classes:
Centrally Acting Sympatholytics (e.g., Clonidine): Overdose creates a distinct toxidrome mimicking opioid poisoning, characterized by CNS depression, bradycardia, hypotension, and miosis. Management focuses on supportive care, with an empirical trial of high-dose naloxone considered reasonable for refractory respiratory depression. We also emphasize that beta-adrenergic antagonists are contraindicated in clonidine withdrawal due to the risk of paradoxical hypertension.
Direct Vasodilators: We analyze agents like sodium nitroprusside, focusing on the critical risk of cyanide and thiocyanate toxicity, managed with hydroxycobalamin or sodium thiosulfate prophylaxis.
Diuretics: Toxicity is predominantly metabolic, presenting as electrolyte abnormalities (e.g., hyponatremia, hypokalemia) and risks like osmotic demyelination syndrome or ventricular dysrhythmias. Acute overdose management is supportive, focusing on correcting fluid and electrolyte status.
RAAS Inhibitors (ACEIs/ARBs/DRIs): Key adverse events include angioedema and teratogenicity. Overdose typically causes hypotension. For refractory hypotension, novel therapies such as methylene blue or vasopressin may be utilized. Combination therapy with multiple RAAS-acting agents is associated with increased risks, including acute kidney injury and stroke.
This module provides the necessary clinical insights to manage the diverse and unique toxicologic presentations of antihypertensive agents.