Chapter 13 - Drugs Affecting Muscle Function
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Chapter 13 - Drugs Affecting Muscle Function






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    Chapter 13 - Drugs Affecting Muscle Function Chapter 13 - Drugs Affecting Muscle Function Presentation Transcript

    • Fundamentals of Pharmacology for Veterinary Technicians Chapter 13 Drugs Affecting Muscle Function
    • Basic Anatomy and Physiology
      • Muscles are tissues that contract to produce movement
      • Muscles are made up of long, slender cells called muscle fibers
      • Muscle fibers are encased in a fibrous sheath
      • Muscle cells are categorized into three types based on their appearance and function:
        • Skeletal
        • Smooth
        • Cardiac
    • Basic Anatomy and Physiology
      • Motor nerves that originate in the spinal cord and terminate in fibers connected to muscle cells activate skeletal muscle
      • A neuromuscular junction is where a motor nerve fiber connects to muscle cells
      • Electrical impulses from the spinal cord travel to the neuromuscular junction, causing release of the neurotransmitter acetylcholine (ACh)
      • ACh binds to specialized receptor sites on the muscle opposite the nerve ending
    • Basic Anatomy and Physiology
      • Depolarization of the muscle occurs, calcium is released, and the muscle contracts
      • ACh is inactivated by acetylcholinesterase
    • Basic Anatomy and Physiology
      • Insert Figure 13-1
    • Drugs That Affect the Skeletal System
      • Anti-inflammatories (Chapter 16)
      • Neuromuscular blockers (drugs that produce paralysis)
      • Skeletal muscle spasmolytics (drugs that reduce muscle spasms)
      • Anabolic steroids (drugs whose tissue building effects can reverse muscle atrophy or wasting)
    • Neuromuscular Blockers
      • Relax the muscles of animals that are undergoing surgery; used to prevent or treat muscle spasms
      • Work by disrupting the transmission of nerve impulses from the motor nerves to skeletal muscle fibers
      • Most are competitive nondepolarizers (compete with ACh for the same receptor sites)
      • Are also called curarizing agents
      • Examples:
        • Pancuronium
        • Atracurium
    • Neuromuscular Blocker Antidotes
      • Competitive nondepolarizers require antidotes once their effects are no longer needed
      • Examples:
        • Neostigmine: competes with ACh for acetylcholinesterase, allowing ACh to accumulate in the neuromuscular junction
        • Pyridostigmine: competes with ACh for attachment to acetylcholinesterase
        • Edrophonium: attaches to acetylcholinesterase, thereby hindering the breakdown of ACh
    • Other Neuromuscular Blockers
      • Other examples:
        • Gallamine
        • Vecuronium
        • Metocurine
      • Antidote:
        • Atropine (because these drugs are cholinergic in nature)
    • Depolarizing Neuromuscular Blockers
      • Depolarizing neuromuscular blockers mimic the action of ACh in muscle fibers, and because they are not destroyed by acetylcholinesterase, their action is prolonged
      • Example:
        • Succinylcholine: binds to the cholinergic receptors
          • No antidote needed; wears off by itself
    • Spasmolytics
      • Break down the muscle spasticity
      • Used to treat acute episodes of muscle spasticity associated with neurological and musculoskeletal disorders (malignant hyperthermia, equine postanesthetic myositis, and traumatic injury)
      • Examples:
        • Methocarbamol: used as an adjunctive therapy for inflammatory and traumatic conditions of skeletal muscle
        • Guaifenesin: used as an adjunct to anesthesia because it relaxes both laryngeal and pharyngeal muscles, thereby making intubation easier
        • Diazepam: used for muscle relaxation
        • Dantrolene: used to prevent and treat malignant hyperthermia
    • Anabolic Steroids
      • Have tissue-building effect (they increase muscle mass)
      • Used to promote growth, counteract postsurgical debility, and treat diseases such as muscular atrophy and orthopedic conditions
      • Examples:
        • Nandrolone (stimulates erythropoiesis and appetite)
        • Stanozolol (improves appetite and weight gain)
        • Boldenone (improves appetite and musculature)
    • Anabolic Steroids
      • To obtain optimal results when giving anabolic steroids, adequate and well-balanced dietary intake is essential
      • Can cause electrolyte imbalance, liver toxicity, behavioral changes, and reproductive abnormalities