Systematic (IUPAC) name
Clinical data
AHFS/ International Drug Names
Pregnancy cat.  ?
Legal status  ?
Routes IV
CAS number 59-98-3 YesY
ATC code C04AB02 M02AX02 QV03AB94
PubChem CID 5504
DrugBank APRD00170
ChemSpider 5303 YesY
KEGG D08614 YesY
Chemical data
Formula C10H12N2 
Mol. mass 160.216 g/mol
SMILES eMolecules & PubChem
 N(what is this?)  (verify)

Tolazoline is a non-selective competitive α-adrenergic receptor antagonist. It is a vasodilator that is used to treat spasms of peripheral blood vessels (as in acrocyanosis). It has also been used successfully as an antidote to reverse the severe peripheral vasoconstriction which can occur as a result of overdose with certain 5-HT2A agonist drugs such as LSD, DOB and Bromodragonfly and can lead to gangrene if untreated.[1][2]

It is however most commonly used in veterinary medicine, to reverse xylazine-induced sedation.[3][4]


Tolazoline, 2-benzyl-2-imidazoline, is synthesized by the heterocyclation of the ethyl ester of iminophenzylacetic acid with ethylene diamine, which forms the desired product. The structure of tolazoline is strikingly similar to α-adrenergic agonists, which are antiedema sympathomimetics.

Tolazoline synthesis.png


  1. ^ Bowen JS, Davis GB, Kearney TE, Bardin J. Diffuse vascular spasm associated with 4-bromo-2,5-dimethoxyamphetamine ingestion. Journal of the American Medical Association 1983 Mar 18;249(11):1477-9. PMID 6827726
  2. ^ Thorlacius K, Borna C, Personne M. Bromo-dragon fly--life-threatening drug. Can cause tissue necrosis as demonstrated by the first described case. (Swedish) Lakartidningen. 2008 Apr 16-22;105(16):1199-200. PMID 18522262
  3. ^ Boothe DM (2001). "Anticonvulsant drugs and analeptic agents". In Adams HR (ed.). Veterinary pharmacology and therapeutics. Ames: Iowa State University Press. pp. 378–9. ISBN 0-8138-1743-9.  Retrieved September 8, 2008 through Google Book Search.
  4. ^ Hall LW, Clarke KW, Trim CM (2001). "Principles of sedation, analgesia and premedication". Veterinary anaesthesia. Philadelphia: W.B. Saunders. pp. 90–1. ISBN 0-7020-2035-4.  Retrieved September 8, 2008 through Google Book Search.