Pharmacotherapeutic group: Centrally acting muscle relaxant.
ATCvet code: QM03BX90
Pharmacodynamic properties
Guaifenesin is a centrally acting muscle relaxant. It causes a selective, reversible relaxing of the skeletal muscles, without loss of consciousness. Guaifenesin selectively blocks nerve impulse transmission in the binding neurons of the spinal cord, brainstem and subcortical regions of the brain. Spinal monosynaptic pathways are unaffected by therapeutic dosages of guaifenesin.
Pharyngeal and laryngeal muscles relax, but when therapeutic dosages are administered, no paralysis of the respiratory muscles (intercostal muscles and diaphragm) occurs. The effect on vital functions such as circulation and breathing is slight.
In addition to its muscle relaxing effect, guaifenesin also has a sedative effect. Guaifenesin has only limited analgesic properties. These effects are probably the result of guaifenesin acting on the extended medulla (formatio reticularis, among others) and subcortical regions of the brain. Due to the limited analgesic and sedative properties of guaifenesin (the animal retains full consciousness), animals must be properly sedated before immobilisation with guaifenesin.
Pharmacokinetic properties
In the case of ponies, a significant difference in half-life between female and male animals has been observed: 60 and 84 minutes respectively after parenteral administration.
In horses, half-life averaged between 75.7-79.2 minutes.
The substance is uniformly distributed over most tissues. Concentrations in the blood of the neonate were approximately 30% of that of the mother immediately after birth.
The muscle relaxing effect starts on average within a few minutes.
The effect of guaifenesin lasts approximately 8-20 minutes. Animals stand again within 45 minutes after administration. The recovery period lengthens substantially after repeated administrations.