January 2009 Update
Dexmedetomidine in cardiac disease: whats the controversy?
Dr. Jo Murrell BVSc. (hons), PhD, DipECVAA, MRCVS.
Alpha 2 adrenoreceptor agonists (α2 agonists) are a group of drugs that are traditionally recommended only for administration to healthy animals, particularly animals without evidence of cardiovascular disease (Murrell and Hellebrekers 2005, Sinclair 2003). This is due to the reduction in cardiac output and increase cardiac afterload that follows α2 agonist administration of (Lawrence et al. 1996a), which may be detrimental to animals with reduced cardiovascular system reserve function. However this dogma is being increasingly questioned in the veterinary profession due to the use of dexmedetomidine in adults with cardiovascular disease (Wijeysundera et al. 2003). But, it is important to remember that cardiovascular diseases in man and animals are not directly comparable, therefore extrapolation of data between species may not be appropriate. Further, the use of dexmedetomidine during cardiac surgery in people is also not without controversy. Two editorials recently appeared in the Journal of Cardiothoracic and Vascular Anaesthesia discussing the evidence for and against the use of dexmedetomidine for infants and children during cardiac surgery. Download the full article.
Dexmedetomidine Publications
Dexmedetomidine has been recently launched across the UK and the rest of Europe as a sedative and premedication agent in dogs and cats. Dexmedetomidine is the first isomer specific drug to be licensed in animals and represents a leap forward in the development and use of stereospecific agents and a move away from the use of non specific racemic mixtures.
The advantages of dexmedetomidine over medetomidine can be briefly listed as follows:
- Greater specificity for the alpha 2 adrenoreceptor compared to medetomidine
- More reliable sedation and greater analgesic potency compared to medetomidine.
- Reduced metabolic burden, due to removal of inactive levomedetomidine from the drug mixture.
- Quicker recoveries from anaesthesia (levomedetomidine has been shown to slow the liver metabolism of other drugs).
The abstracts that I have chosen to showcase in the first issue of the educational updates describe the use of dexmedetomidine for circumstances for which it is not usually employed in veterinary anaesthesia; prevention of post-operative shivering, use during ophthalmic surgery to lower or manage intraocular pressure. Intranasal use of dexmedetomidine and a study describing a potential mechanism for dexmedetomidine mediated analgesia is also described.
