Adverse EffectsAll of the responses summarized in Table 14.2 can beproduced by administration of ganglionic blockingagents. Many of these responses are undesirable effectsthat limit the therapeutic usefulness of these agents.Mild untoward responses include mydriasis, difficultyin vision accommodation, dry mouth, urinary hesitancy,constipation, diarrhea, abdominal discomfort, anorexia,and syncope. More serious but less frequent distur-bances include marked hypotension, constipation, par-alytic ileus, urinary retention, and anginal pain.INDIVIDUAL AGENTSTrimethaphanTrimethaphan camsylate (Arfonad) is an extremelyshort-acting agent whose major therapeutic use is in theproduction of controlled hypotension in certain surgicalSiteEffect of Ganglionic BlockadeTissues predominantly under parasympathetic (cholinergic) toneMyocardiumAtrium; S-A nodeEyeIrisCiliary muscleGI tractUrinary bladderSalivary glandTissues predominantly under sympathetic (adrenergic) toneMyocardiumVentriclesBlood vesselsArteriolesVeinsSweat glandsaaAnatomically sympathetic; transmitter is ACh.Predominant AutonomicTone at VariousNeuroeffector Junctions andthe Effect Produced byGanglionic BlockadeTABLE14.2TachycardiaMydriasisCycloplegiaDecrease in tone and motility; con-stipationUrinary retentionDry mouthDecrease in contractile forceVasodilation; increase in peripheralblood flow; hypotensionVasodilation; pooling of blood; de-crease in venous return; decreasein cardiac outputDecrease in secretion
procedures and in the emergency treatment of hyper-tensive crisis. Continuous infusion may be employed tomaintain its antihypertensive effect, especially in pa-tients with an acute dissecting aortic aneurysm. Much ofthe decrease in blood pressure following trimethaphanadministration is thought to be due to its direct vasodi-lating properties.Trimethaphan can produce prolonged neuromus-cular blockade in some patients, and therefore, itshould be used with caution as a hypotensive agentduring surgery. It also has been reported to potentiatethe neuromuscular blocking action of tubocurarine,and because of its histamine-releasing properties,trimethaphan should be used with caution in patientswith allergies.MecamylamineMecamylamine hydrochloride (Inversine) is a secondaryamine 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 boththe blood-brain and placental barriers; its distribution isnot confined to the extracellular space. High concentra-tions of the drug accumulate in the liver and kidney, andit is excreted unchanged by the kidney.In contrast to mostof the highly ionized ganglionic blocking agents, mecamy-lamine can produce central nervous system effects, in-cluding tremors, mental confusion, seizures, mania, anddepression.The mechanism by which these central effectsare produced is unclear. Mecamylamine is rarely used to-day as an antihypertensive drug because it blocks bothparasympathetic and sympathetic ganglia.
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Term
Spring
Professor
odhis
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