Where is guaifenesin most commonly utilized?
in large animal anesthesia
(can find it in small animal medicien as an expectorant combined with dextromethorphan - Cough Tabs)
How is guaifenesin most commonly supplied?
as a bacteriostatic-bactericidal powder. It is dissolved in 5% dextrose, sterile water, or saline. It can EASILY precipitate out of solution and is compatible in solution with other anesthetic drugs
What is the MoA of guaifenesin?
- centrally acting skeletal muscle relaxant
- binds to specific inhibitory neurotransmitter sites (GABA) in the brain and spinal cord
Where exactly does guaifenesin suppress in the CNS?
- selective depression or blockade of nerve impulse transmission at internuncial neuron level of spinal cord, brainstem, and subcortical areas of the brain
How and where is guaifenesin metabolised and excreted?
- metabolized in the liver
- glucuronidation
- excretion in the urine
What is the pharmacokinetic profile of guaifenesin?
- IV alone, recumbency may occur within 2 minutes and last 6 minutes without unconsciousness
- sedation could last 15-30 minutes
- rapid elimination in horses
Has a gender difference been identified in regards to guaifenesin’s pharmacokinetic profile?
yes! female poines have a shorter half-life compared to male ponies (60 min vs 85 min)
What is the terminal half life of guaifenesin in horses?
t1/2 = 84.5min, clearance of 8.2mL/kg/min
Does guaifenesin have a toxicity profile?
while it has a wide therapeutic margin, concentration of drug is species important
in horses, what is the dose to produce recumbency?
100-150mg/kg, which is ~20-30% of the dose to cause cardiopulmonary depression. Overdose COULD cause respiratory depression and muscle rigidity.
What are the CNS effects of guaifenesin?
- centrally acting skeletal muscle relaxant, CNS depressant effects
What are the CV effects of guaifenesin?
Minimal to no CV effects at clinical dosages
What are the respiratory effects of guaifenesin?
minimal to no respiratory depressant effects at clinical dosages: PaCO2 is unchanged, PaO2 decreased after administration to achieve lateral recumbency in horses.
NOTE: respiratory depression noted in donkeys
What are the musculoskeletal effects of guaifenesin?
skeletal muscle relaxation with no effect on cardiac or smooth muscle
NOTE: 33-88 mg/kg IV for muscle relaxation in dogs, 100-160mg/kg IV in horses
GI effects of guaifenesin?
high doses may result in vomiting
What are the urinary effects of guaifenesin?
no known renal effects
What is a major side effect of guaifenesin?
hemolysis!! Solutions greater than 5% can induce hemolysis in cattle and greater than 10% can induce hemolysis in horses
Can analgesia result from guaifenesin?
Very minimal per a 1973 Funk study
Can you give guaifenesin to a pregnant patient?
guaifenesin crosses the placental barrier with fetal concentration being approximately 30% of maternal circulation. Foals at birth do not show significant depression
Anything special about donkeys and guaifenesin?
donkeys have a lower clearance and therefore a longer half life than horses
