Last updated
Clinical data
AHFS/ International Drug Names
Routes of
ATC code
  • 2-Benzyl-4,5-dihydro-1H-imidazole
CAS Number
PubChem CID
CompTox Dashboard (EPA)
ECHA InfoCard 100.000.408 OOjs UI icon edit-ltr-progressive.svg
Chemical and physical data
Formula C10H12N2
Molar mass 160.220 g·mol−1
3D model (JSmol)
  • N\1=C(\NCC/1)Cc2ccccc2
  • InChI=1S/C10H12N2/c1-2-4-9(5-3-1)8-10-11-6-7-12-10/h1-5H,6-8H2,(H,11,12) Yes check.svgY

Tolazoline is a non-selective competitive α-adrenergic receptor antagonist. [1] It is a vasodilator that is used to treat spasms of peripheral blood vessels (as in acrocyanosis). It has also been used (in conjunction with sodium nitroprusside) 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 25I-NBOMe,[ citation needed ] DOB and Bromodragonfly (prolonged severe vasoconstriction can lead to gangrene if untreated). [2] [3]

It is however most commonly used in veterinary medicine, to reverse xylazine-induced sedation. [4] [5]

Related Research Articles

Chlorpromazine Antipsychotic medication

Chlorpromazine (CPZ), marketed under the brand names Thorazine and Largactil among others, is an antipsychotic medication. It is primarily used to treat psychotic disorders such as schizophrenia. Other uses include the treatment of bipolar disorder, severe behavioral problems in children including those with attention deficit hyperactivity disorder, nausea and vomiting, anxiety before surgery, and hiccups that do not improve following other measures. It can be given by mouth, by injection into a muscle, or into a vein.

Local anesthetic

A local anesthetic (LA) is a medication that causes absence of pain sensation. In the context of surgery, a local anesthetic creates an absence of pain in a specific location of the body without a loss of consciousness, as opposed to a general anesthetic. When it is used on specific nerve pathways, paralysis also can be achieved.

A muscle relaxant is a drug that affects skeletal muscle function and decreases the muscle tone. It may be used to alleviate symptoms such as muscle spasms, pain, and hyperreflexia. The term "muscle relaxant" is used to refer to two major therapeutic groups: neuromuscular blockers and spasmolytics. Neuromuscular blockers act by interfering with transmission at the neuromuscular end plate and have no central nervous system (CNS) activity. They are often used during surgical procedures and in intensive care and emergency medicine to cause temporary paralysis. Spasmolytics, also known as "centrally acting" muscle relaxant, are used to alleviate musculoskeletal pain and spasms and to reduce spasticity in a variety of neurological conditions. While both neuromuscular blockers and spasmolytics are often grouped together as muscle relaxant, the term is commonly used to refer to spasmolytics only.

Peripheral artery disease Medical condition

Peripheral artery disease (PAD) is an abnormal narrowing of arteries other than those that supply the heart or brain. When narrowing occurs in the heart, it is called coronary artery disease, and in the brain, it is called cerebrovascular disease. Peripheral artery disease most commonly affects the legs, but other arteries may also be involved – such as those of the arms, neck, or kidneys. The classic symptom is leg pain when walking which resolves with rest, known as intermittent claudication. Other symptoms include skin ulcers, bluish skin, cold skin, or abnormal nail and hair growth in the affected leg. Complications may include an infection or tissue death which may require amputation; coronary artery disease, or stroke. Up to 50% of people with PAD do not have symptoms.

Propofol Intravenous medication used in anaesthesia

Propofol, marketed as Diprivan, among other names, is a short-acting medication that results in a decreased level of consciousness and a lack of memory for events. Its uses include the starting and maintenance of general anesthesia, sedation for mechanically ventilated adults, and procedural sedation. It is also used for status epilepticus if other medications have not worked. It is given by injection into a vein, and the maximum effect takes about two minutes to occur and typically lasts five to ten minutes. Propofol is also used for medical assistance in dying in Canada.

Midazolam Benzodiazepine used for anesthesia and procedural sedation

Midazolam, sold under the brand name Versed, among others, is a benzodiazepine medication used for anesthesia, procedural sedation, trouble sleeping, and severe agitation. It works by inducing sleepiness, decreasing anxiety, and causing a loss of ability to create new memories. It is also useful for the treatment of seizures. Midazolam can be given by mouth, intravenously, by injection into a muscle, by spraying into the nose, or through the cheek. When given intravenously, it typically begins working within five minutes; when injected into a muscle, it can take fifteen minutes to begin working. Effects last between one and six hours.

2,5-Dimethoxy-4-bromoamphetamine Chemical compound

Dimethoxybromoamphetamine (DOB), also known as brolamfetamine (INN) and bromo-DMA, is a psychedelic drug and substituted amphetamine of the phenethylamine class of compounds. DOB was first synthesized by Alexander Shulgin in 1967. Its synthesis and effects are documented in Shulgin's book PiHKAL: A Chemical Love Story.

Cyclobenzaprine Muscle relaxant medication

Cyclobenzaprine, sold under the brand name Flexeril among others, is a medication used for muscle spasms from musculoskeletal conditions of sudden onset. It is not useful in cerebral palsy. It is taken by mouth. Use is not recommended for more than a few weeks.


Acepromazine, acetopromazine, or acetylpromazine is a phenothiazine derivative antipsychotic drug. It was used in humans during the 1950s as an antipsychotic, but is now almost exclusively used on animals as a sedative and antiemetic. Its closely related analogue, chlorpromazine, is still used as an antipsychotic in humans. Acepromazine is used primarily as a chemical restraint in hyperactive or fractious animals.

Reserpine Drug used to treat high blood pressure

Reserpine is a drug that is used for the treatment of high blood pressure, usually in combination with a thiazide diuretic or vasodilator. Large clinical trials have shown that combined treatment with reserpine plus a thiazide diuretic reduces mortality of people with hypertension. Although the use of reserpine as a solo drug has declined since it was first approved by the FDA in 1955, the combined use of reserpine and a thiazide diuretic or vasodilator is still recommended in patients who do not achieve adequate lowering of blood pressure with first-line drug treatment alone. The reserpine-hydrochlorothiazide combo pill was the 17th most commonly prescribed of the 43 combination antihypertensive pills available In 2012.


Xylazine is an analogue of clonidine and an agonist at the α2 class of adrenergic receptor. It is used for sedation, anesthesia, muscle relaxation, and analgesia in animals such as horses, cattle and other non-human mammals. Veterinarians also use xylazine as an emetic, especially in cats.


Phentolamine, sold under the brand name Regitine among others, is a reversible nonselective α-adrenergic antagonist.


Butorphanol is a morphinan-type synthetic agonist–antagonist opioid analgesic developed by Bristol-Myers. Butorphanol is most closely structurally related to levorphanol. Butorphanol is available as the tartrate salt in injectable, tablet, and intranasal spray formulations. The tablet form is only used in dogs, cats and horses due to low bioavailability in humans.

The alpha-2 (α2) adrenergic receptor is a G protein-coupled receptor (GPCR) associated with the Gi heterotrimeric G-protein. It consists of three highly homologous subtypes, including α2A-, α2B-, and α2C-adrenergic. Some species other than humans express a fourth α2D-adrenergic receptor as well. Catecholamines like norepinephrine (noradrenaline) and epinephrine (adrenaline) signal through the α2-adrenergic receptor in the central and peripheral nervous systems.

Autonomic dysreflexia (AD) is a potential medical emergency classically characterized by uncontrolled hypertension and bradycardia, although tachycardia is known to commonly occur. AD occurs most often in individuals with spinal cord injuries with lesions at or above the T6 spinal cord level, although it has been reported in patients with lesions as low as T10. Guillain–Barré syndrome may also cause Autonomic Dysreflexia.


Dexmedetomidine, sold under the trade name Precedex among others, is an anxiolytic, sedative, and pain medication. Dexmedetomidine is notable for its ability to provide sedation without risk of respiratory depression and can provide cooperative or semi-rousable sedation.


Diprenorphine, also known as diprenorfin, is a non-selective, high-affinity, weak partial agonist of the μ- (MOR), κ- (KOR), and δ-opioid receptor (DOR) which is used in veterinary medicine as an opioid antagonist. It is used to reverse the effects of super-potent opioid analgesics such as etorphine and carfentanil that are used for tranquilizing large animals. The drug is not approved for use in humans.


Detomidine is an imidazole derivative and α2-adrenergic agonist, used as a large animal sedative, primarily used in horses. It is usually available as the salt detomidine hydrochloride. It is a prescription medication available to veterinarians sold under the trade name Dormosedan.

Atipamezole Synthetic α2 adrenergic receptor antagonist

Atipamezole (brand name Antisedan, also available in generic forms as Revertidine, is a synthetic α2 adrenergic receptor antagonist indicated for the reversal of the sedative and analgesic effects of dexmedetomidine and medetomidine in dogs. Its reversal effect works by competing with the sedative for α2-adrenergic receptors and displacing them. It is mainly used in veterinary medicine, and while it is only licensed for dogs and for intramuscular use, it has been used intravenously, as well as in cats and other animals. There is a low rate of side effects, largely due to atipamezole's high specificity for the α2-adrenergic receptor. Atipamezole has a very quick onset, usually waking an animal up within 5 to 10 minutes.


Bromoketoprogesterone (BKP), also known as 9α-bromo-11-oxoprogesterone (BOP), and known by the tentative brand name Braxarone (Squibb), is an orally active progestin which does not appear to have been marketed.


  1. Aronson, J. K. (2016). Meyler's side effects of drugs : the international encyclopedia of adverse drug reactions and interactions. Amsterdam: Elsevier Science. ISBN   978-0-444-53717-1. OCLC   927102885. Tolazoline is an α2 adrenoceptor antagonist that increases skin blood flow in healthy subjects and has been used to relieve acute vasospasm.
  2. Bowen JS, Davis GB, Kearney TE, Bardin J (March 1983). "Diffuse vascular spasm associated with 4-bromo-2,5-dimethoxyamphetamine ingestion". JAMA. 249 (11): 1477–9. doi:10.1001/jama.1983.03330350053028. PMID   6827726.
  3. Thorlacius K, Borna C, Personne M (2008). "[Bromo-dragon fly--life-threatening drug. Can cause tissue necrosis as demonstrated by the first described case]". Lakartidningen (in Swedish). 105 (16): 1199–200. PMID   18522262.
  4. 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 8 September 2008.
  5. 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.