Changes

Alpha-2 agonists have sedative, anxiolytic and analgesic effects.

Alpha-2 agonists have sedative, anxiolytic and analgesic effects.

==Actions==

==Actions==

Alpha-2 agonists have a wide range of actions, due to the presence of alpha-2 receptors throughout the body. The actions most useful pharmacologically are '''sedation''', '''anxiolysis''' and '''analgesia'''. The drugs also have a huge '''anaesthetic sparing effect''', reducing MAC by 50-95%. They also give '''muscle relaxtion'''.

Alpha-2 agonists have a wide range of actions, due to the presence of alpha-2 receptors throughout the body. The most useful pharmacological actions are '''sedation''', '''anxiolysis''' and '''analgesia'''. The drugs also have a huge '''anaesthetic sparing effect''', reducing MAC by 50-95%. They also give '''muscle relaxation'''.

Other systems affected by alpha-2 agonists include:

Other systems affected by alpha-2 agonists include:

* <u>Cardiovascular System</u>

* <u>Cardiovascular System</u>

** Post synaptic alpha-2 effects and non-selective action on alpha-1 receptors cause vasoconstriction, hypertension and reflex bradycardia.

** Post synaptic alpha-2 effects and non-selective action on alpha-1 receptors cause vasoconstriction, hypertension and reflex bradycardia.

** Pre-synaptic inhibition of noradrenaline release gives a reduced sympathetic outflow. This dexreases heart rate and offsets vasoconstriction.  

** Pre-synaptic inhibition of noradrenaline release gives a reduced sympathetic outflow. This decreases heart rate and offsets vasoconstriction.  

* <u>Respiratory System</u>

* <u>Respiratory System</u>

** The drugs cause mild depression of the respiratory systsem.

** The drugs cause mild depression of the respiratory system.

** The response to hypercapnoea is reduced.

** The response to hypercapnia is reduced.

* <u>Gastrointestinal Tract</u>

* <u>Gastrointestinal Tract</u>

** Alpha-2 agonists cause extreme vomitting in dogs and cats. [[#Xylazine|Xylazine]] is the worst culprit for this.

** Alpha-2 agonists cause extreme vomiting in dogs and cats. [[#Xylazine|Xylazine]] is the worst culprit for this.

** Huge reductions in gut motility occur following drug administration, as well as decreased salivation and secretion.

** Huge reductions in gut motility occur following drug administration, as well as decreased salivation and secretion.

* <u>Endocrine System</u>

* <u>Endocrine System</u>

===Xylazine===

===Xylazine===

Xylazine is available as a 2% solution for use in cattle, horses, cats and dogs. A 10% solution for horses may be used for pre-medication prior to [[NMDA Antagonists|ketamine]] anaesthesia or analgesia in, for example, colic cases. A powdered form is also licensed in horses. Intramuscular and intravenous administration both have a short onset time of 5 minutes. The peak effect occurs 10 minutes after intramuscular injection, and the duration of the drug's actions is 20 mins following intravenous administration. Intravenous use is only licensed in dogs and cats.

Xylazine is available as a 2% solution for use in cattle, horses, cats and dogs. A 10% solution for horses may be used for pre-medication prior to [[Dissociative Agents#Ketamine|ketamine]] anaesthesia or analgesia in, for example, colic cases. A powdered form is also licensed in horses. Intramuscular and intravenous administration both have a short onset time of 5 minutes. The peak effect occurs 10 minutes after intramuscular injection, and the duration of the drug's actions is 20 mins following intravenous administration. Intravenous use is only licensed in dogs and cats.

Xylazine must not be used in the last month of pregnancy, since it causes uterine contractions. The drug is also arrhythmogenic.

Xylazine must not be used in the last month of pregnancy, since it causes uterine contractions. The drug is also arrhythmogenic.

===Medetomidine===

===Medetomidine===

Medetomidine is available as a 1mg/ml solution for use in dogs and cats.It is non irritant so therefore can be administered via an intravenous, intramuscular or subcutaneous route. Intravenous administration produces the most rapid effects, and the least amount of vomiting compared to other routes of administration. When given via an intramuscular route, maximal effects are not seen until 20 minutes after administration, although some sedation may be seen as early as 5 minutes. It is a very effective premedicant reducing the MAC of inhalation agents, and can be used in combination with [[NMDA Antagonists|ketamine]] in cats to induce anaethesia.  

Medetomidine is available as a 1mg/ml solution for use in dogs and cats.It is non irritant so therefore can be administered via an intravenous, intramuscular or subcutaneous route. Intravenous administration produces the most rapid effects, and the least amount of vomiting compared to other routes of administration. When given via an intramuscular route, maximal effects are not seen until 20 minutes after administration, although some sedation may be seen as early as 5 minutes. It is a very effective premedicant reducing the MAC of inhalation agents, and can be used in combination with [[Dissociative Agents#Ketamine|ketamine]] in cats to induce anaethesia.