Ganglionic Blocking Agents - Sympatholytic Drug Cardiovascular Poison

 Ganglionic Blocking Agents

Ganglionic blocking agents such as hexamethonium, meca-mylamine, pempidine, pentolinium, and trimethaphan areeffective antihypertensive drugs, but their use is now curtailed to the treatment of hypertension associated with dissecting aneurysm of aorta. They interfere with neurotransmission in sympathetic and parasympathetic ganglia.

Adverse Effects

·              Constipation (sometimes diarrhoea), paralytic ileus, urinary retention, impotence, dry mouth, postural hypotension, tachycardia, drowsiness, and blurred vision.

·              Various arrhythmias (AV block, left bundle branch block, ventricular fibrillation) have been reported with trimetha-phan therapy. Respiratory arrest has also been reported following high doses. Chronic therapy has led to coughing, dyspnoea, and intra-alveolar and interstitial pulmonary fibrosis.

Clinical (Toxic) Features

1.Respiratory arrest can occur.

2.Mydriasis, urinary retention, and seizures may occur, espe-cially following large doses of mecamylamine. Tremor, hallucinations, and confusion may also follow high dose mecamylamine.

Treatment

·              Intravenous crystalloid boluses.

·              Attempt initial control of seizures with a benzodiazepine (diazepam or lorazepam). If seizures persist or recur admin- ister phenobarbitone.

·              Physostigmine or neostigmine (0.5 to 1 mg IV, slowly) have proved useful in some cases.

·              Gastrointestinal function may be restored with cholinergic agents such as bethanechol.