Trimethaphan camsylate (Arfonad) is an extremely short-acting agent whose major therapeutic use is in the production of controlled hypotension in certain surgical procedures and in the emergency treatment of hyper-tensive crisis. Continuous infusion may be employed to maintain its antihypertensive effect, especially in pa-tients with an acute dissecting aortic aneurysm. Much of the decrease in blood pressure following trimethaphan administration is thought to be due to its direct vasodi-lating properties.
Trimethaphan can produce prolonged neuromus-cular blockade in some patients, and therefore, it should be used with caution as a hypotensive agent during surgery. It also has been reported to potentiate the neuromuscular blocking action of tubocurarine, and because of its histamine-releasing properties, trimethaphan should be used with caution in patients with allergies.
Mecamylamine hydrochloride (Inversine) is a secondary amine and can therefore easily penetrate cell membranes. Its absorption from the gastrointestinal tract is more com-plete than that of the quaternary ammonium compounds. Mecamylamine is well absorbed orally and crosses both the blood-brain and placental barriers; its distribution is not confined to the extracellular space. High concentra-tions of the drug accumulate in the liver and kidney, and it is excreted unchanged by the kidney. In contrast to most of the highly ionized ganglionic blocking agents, mecamy-lamine can produce central nervous system effects, in-cluding tremors, mental confusion, seizures, mania, and depression. The mechanism by which these central effects are produced is unclear. Mecamylamine is rarely used to-day as an antihypertensive drug because it blocks both parasympathetic and sympathetic ganglia.