Transcript No Slide Title - Delmar Cengage Learning

Fundamentals of Pharmacology
for Veterinary Technicians
Chapter 13
Drugs Affecting Muscle Function
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
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
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
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
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Basic Anatomy and Physiology
• Depolarization of the muscle occurs,
calcium is released, and the muscle
contracts
• ACh is inactivated by
acetylcholinesterase
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Basic Anatomy and Physiology
Insert Figure 13-1
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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)
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
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
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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
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Other Neuromuscular Blockers
• Other examples:
– Gallamine
– Vecuronium
– Metocurine
• Antidote:
– Atropine (because these drugs are
cholinergic in nature)
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
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
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
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
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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)
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Anabolic Steroids
• To obtain optimal results when giving
anabolic steroids, adequate and wellbalanced dietary intake is essential
• Can cause electrolyte imbalance,
liver toxicity, behavioral changes,
and reproductive abnormalities
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