ganglionic blocking agent, any one of a group of drugs prescribed to produce controlled hypotension, as required in certain surgical procedures or in emergency management of hypertensive crisis. The drugs act by occupying receptor sites (nicotinic neuronal receptors) on sympathetic and parasympathetic autonomic ganglia, preventing a response of these nerves to the action of acetylcholine liberated by the presynaptic nerve endings. Mecamylamine is the most commonly prescribed ganglionic blocking agent. These drugs are used with great caution in treating patients who are affected with coronary, cerebrovascular, or renal insufficiency or who have a history of severe allergy. Adverse reactions to the drugs include sudden marked hypotension, paralytic ileus, urinary retention, constipation, visual disturbances, heartburn, and nausea.
