Lect 12

• Pre-anesthetics or muscle relaxants are drugs that act on the Central Nervous System (CNS).
• Anait S. Levenson, M.D., Ph.D, is a lecturer on drugs acting on the Central Nervous System (CNS).
• The lecture on pre-anesthetics or muscle relaxants was held on October 9, 2023.
• The office hours for Anait S. Levenson, M.D., Ph.D, are by appointment, which can be arranged by sending an email to [e-mail].
• An adjunct or pre-anesthetic is a drug that is not a true anesthetic, but that is used during anesthesia to produce other desired effects such as sedation, muscle relaxation, analgesia, reversal, neuromuscular blockade, or parasympathetic blockade.
• Pre-anesthetics or muscle relaxants are used prior to the administration of an anesthetic agent to make anesthesia safe and more agreeable to the patient.
• Central acting spasmolytics also include Mathocarbamol, an analog of Guaifenesin, used to treat muscle spasms in dogs and cats.
• Centrally acting muscle relaxants include spasmolytics such as benzodiazepines, GABA agonists, and α2 agonists.
• Centrally acting muscle relaxants have a spinal cord site of spasmolytic action.
• Peripheral acting muscle relaxants have sedative and musculoskeletal relaxant properties.
• The mechanism of action of Baclofen is to mimic GABA (agonist, GABA B ) within the spinal cord and works by depressing afferent reflex activity at the spinal cord level, thereby reducing skeletal muscle spasm.
• Guaifenesin has mild sedative and analgesic properties and decreases blood pressure in horses, but minimal effect on heart rate.
• Centrally acting muscle relaxants have sedative and musculoskeletal relaxant properties.
• Adverse effects of Guaifenesin include allergic reaction in horses and overdose can cause bradycardia, hypotension, extensor rigidity, apnea, and cardiac arrest.
• Baclofen is a dangerous muscle relaxant in dogs and cats and is used to treat urinary retention by reducing urethral resistance and gastroesophageal reflux.
• Neuromuscular Blocking Agents (NMBAs) are a type of centrally acting muscle relaxant.
• Side effects of centrally acting muscle relaxants include significant sedation but milder than that produced by other sedative-hypnotic drugs at doses that induce equivalent muscle relaxation.
• Central acting spasmolytics include Guaifenesin, which is used in combination with thiobarbiturates and ketamine for induction of anesthesia in horses, cattle, and swine.
• Neuromuscular Blocking Agents (NMBAs) are a type of peripheral acting muscle relaxant.
• Adverse effects of Baclofen include allergic reactions, dizziness, drowsiness, headache, nausea, vomiting, and diarrhea.
• Baclofen has a narrow margin of safety, clinical use is infrequent, causes loss of the gag reflex putting dogs at high risk for aspiration, and can cause severe vomiting, seizures, and cardiac arrest.
• Pre-anesthetic medications should be used appropriately to minimize stress, cardiopulmonary depression, and the adverse effects produced by anesthetic administration.
• Medetomidine produces CNS depression, analgesia, and muscle relaxation for 30 minutes.
• Xylazine, Medetomidine, Detomidine, and Dexmedetomidine are examples of α2-adrenergic agonists.
• Detomidine produces CNS depression, analgesia, and muscle relaxation for 30 minutes.
• Pre-anesthetic medications should be administered prior to minor procedures and can be readily reversed with α2-antagonists.
• Non-controlled agents such as α2-adrenergic agonists produce sedation, analgesia, and muscle relaxation without producing general anesthesia.
• Pre-anesthetic medications generally include combinations of drugs from multiple categories such as opioids, tranquilizers, muscle relaxants, and anticholinergics.
• Dexmedetomidine produces CNS depression, analgesia, and muscle relaxation for 30 minutes.
• Medetomidine, Detomidine, and Dexmedetomidine produce CNS depression, analgesia, and muscle relaxation without producing general anesthesia.
• Xylazine, Medetomidine, Detomidine, and Dexmedetomidine cause early phase dose-dependent vasoconstriction and hypertension, late phase decrease cardiac output hypotension, and cardiac arrhythmias.
• The effects of Medetomidine, Detomidine, and Dexmedetomidine are dose-dependent.
• Pre-anesthetic medications should not be used in place of anesthetic drugs but rather as an adjunct to safe anesthetic management.
• Anticholinergic agents prevent profuse salivation and bradycardia.
• The effects of Medetomidine, Detomidine, and Dexmedetomidine wear off after 30 minutes.
• Central muscle relaxants provide muscle relaxation during anesthesia.
• Pre-anesthetic medications include sedatives, tranquilizers, and muscle relaxants.
• Xylazine produces sedation, analgesia, and muscle relaxation without producing general anesthesia.
• Sedatives and tranquilizers provide pre-operative sedation and amnesia and help to prevent or counteract the CNS stimulation caused by some anesthetics.
• Xylazine is more potent and selective than Medetomidine and is commonly used in Vet Med.