Chapter 13 - Drugs Affecting Muscle Function


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Chapter 13 - Drugs Affecting Muscle Function

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