Trimetaphan camsilate
Skeletal formulas of trimetaphan camsilate
Ball-and-stick models of the component ions of trimetaphan camsilate
Clinical data
Trade namesArfonad
Routes of
Oral, IM, IV
ATC code
Pharmacokinetic data
ExcretionRenal, mostly unchanged
  • 3,5-dibenzyl-4-oxo-8λ4-thia-3,5-diazatricyclo[,6]undecan-8-ylium (7,7-dimethyl-2-oxobicyclo[2.2.1]heptan-1-yl)methanesulfonate
CAS Number
PubChem CID
CompTox Dashboard (EPA)
ECHA InfoCard100.000.633 Edit this at Wikidata
Chemical and physical data
FormulaC22H25N2OS (free base)
Molar mass365.52 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]

Therapeutic uses

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.


This article includes a list of general references, but it lacks sufficient corresponding inline citations. Please help to improve this article by introducing more precise citations. (September 2018) (Learn how and when to remove this message)
  1. ^ Bause GS (1 August 2017). "From Coenzyme R to "Arfonad" and from Vitamin H to Hypotension". Anesthesiology. 127 (2): 381–381. doi:10.1097/ALN.0000000000001771. ISSN 0003-3022.
  2. ^ Dale RC, Schroeder ET (July 1976). "Respiratory paralysis during treatment of hypertension with trimethaphan camsylate". Archives of Internal Medicine. 136 (7): 816–8. doi:10.1001/archinte.1976.03630070060018. PMID 938175.

Further reading