Trimetaphan camsilate

Trimetaphan camsilate

Clinical data
Trade names	Arfonad
Routes of administration	Oral, IM, IV
ATC code	C02BA01 (WHO)
Pharmacokinetic data
Excretion	Renal, mostly unchanged
Identifiers
IUPAC name 3,5-dibenzyl-4-oxo-8λ4-thia-3,5-diazatricyclo[6.3.0.02,6]undecan-8-ylium (7,7-dimethyl-2-oxobicyclo[2.2.1]heptan-1-yl)methanesulfonate
CAS Number	68-91-7 Y
PubChem CID	23576
DrugBank	DB01116 N
UNII	8W556014K9
KEGG	D00612
ChEMBL	ChEMBL1245 N
CompTox Dashboard (EPA)	DTXSID3023710
ECHA InfoCard	100.000.633
Chemical and physical data
Formula	C22H25N2OS (free base)
Molar mass	365.52 g·mol−1
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Trimetaphan camsilate (INN) or trimethaphan camsylate (USAN), trade name Arfonad, is a sympatholytic drug used in rare circumstances to lower blood pressure.

Trimetaphan is a ganglionic blocker: it counteracts cholinergic transmission at a specific type of nicotinic acetylcholine receptors in the autonomic ganglia and therefore blocks both the sympathetic nervous system and the parasympathetic nervous system. It acts as a non-depolarizing competitive antagonist at the nicotinic receptor, is short-acting, and is given intravenously.

It was discovered by Leo Sternbach.^[1]

Trimetaphan is a sulfonium compound and therefore carries a positive charge. Being charged, it cannot cross lipid cell membranes, such as those that comprise the blood–brain barrier. Due to this, trimethaphan does not have any effect on the central nervous system.

The ciliary muscle of the eye functions to round the lens for accommodation and is controlled mainly by parasympathetic system input. With administration of a ganglion-blocking drug, the ciliary muscle cannot contract (cycloplegia) and the patient loses the ability to focus their eyes.

Trimetaphan has a strong effect on the cardiovascular system. The size of blood vessels is primarily controlled by the sympathetic nervous system. Loss of sympathetic system input to the blood vessels causes them to get larger (vasodilation) which has the effect of lowering blood pressure. Postural hypotension is a common side effect of such drugs. Trimethaphan causes a histamine release which further lowers blood pressure. Effects on the heart include a decreased force of contraction and an increase in heart rate (tachycardia). Reflexive tachycardia can be diminished or undetected because trimetaphan is also blocking the sympathetic ganglia innervating the heart.

The motility of the gastrointestinal tract is regulated by the parasympathetic system, and blockage of this input results in diminished motility and constipation.

A rare side effect of trimethaphan administration is sudden respiratory arrest. The mechanism behind it is unknown, as trimethaphan does not appear to block neuromuscular transmission, and respiratory arrest is not an expected consequence of ganglionic blockage.^[2]

The therapeutic uses of trimetaphan are very limited due to the competition from newer drugs that are more selective in their actions and effects produced. It is occasionally used to treat a hypertensive crisis and dissecting aortic aneurysm, to treat pulmonary edema, and to reduce bleeding during neurosurgery.

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