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Neurology aNd Special SeNSeS ` neurology—PhArmACology Neurology aNd Special SeNSeS ` neurology—PhArmACology SecTioN iii 551
Neuromuscular Muscle paralysis in surgery or mechanical ventilation. Selective for Nm nicotinic receptors at
blocking drugs neuromuscular junction but not autonomic Nn receptors.
Depolarizing Succinylcholine—strong ACh receptor agonist; produces sustained depolarization and prevents
neuromuscular muscle contraction.
blocking drugs Reversal of blockade:
Phase I (prolonged depolarization)—no antidote. Block potentiated by cholinesterase inhibitors.
Phase II (repolarized but blocked; ACh receptors are available, but desensitized)—may be
reversed with cholinesterase inhibitors.
Complications include hypercalcemia, hyperkalemia, malignant hyperthermia.
Nondepolarizing Atracurium, cisatracurium, pancuronium, rocuronium, tubocurarine, vecuronium—competitive
neuromuscular ACh antagonist.
blocking drugs Reversal of blockade—cholinesterase inhibitors (eg, neostigmine, edrophonium) are given with
anticholinergics (eg, atrophine, glycopyrrolate) to prevent muscarinic effects, such as bradycardia.
Spasmolytics, antispasmodics
drug meChAnism CliniCAl use notes
Baclofen GABA receptor agonist in Muscle spasticity, dystonia, Acts on the back (spinal cord).
B
spinal cord. multiple sclerosis.
Cyclobenzaprine Acts within CNS, mainly at the Muscle spasticity. Centrally acting. Structurally
brain stem. related to TCAs. May cause
anticholinergic side effects,
sedation.
Dantrolene Prevents release of Ca from Malignant hyperthermia Acts Directly on muscle.
2+
sarcoplasmic reticulum of (toxicity of inhaled anesthetics
skeletal muscle by inhibiting and succinylcholine) and
the ryanodine receptor. neuroleptic malignant
syndrome (toxicity of
antipsychotic drugs).
Tizanidine α agonist, acts centrally. Muscle spasticity, multiple
2
sclerosis, ALS, cerebral palsy.
Opioid analgesics
meChAnism Act as agonists at opioid receptors (μ = β-endorphin, δ = enkephalin, κ = dynorphin) to modulate
synaptic transmission—close presynaptic Ca channels, open postsynaptic K channels
2+
+
synaptic transmission. Inhibit release of ACh, norepinephrine, 5-HT, glutamate, substance P.
eFFiCACy Full agonist: morphine, heroin, meperidine, methadone, codeine, fentanyl.
Partial agonist: buprenorphine.
Mixed agonist/antagonist: nalbuphine, pentazocine, butorphanol.
Antagonist: naloxone, naltrexone, methylnaltrexone.
CliniCAl use Moderate to severe or refractory pain, diarrhea (loperamide, diphenoxylate), acute pulmonary
edema, maintenance programs for heroin addicts (methadone, buprenorphine + naloxone).
AdVerse eFFeCts Nausea, vomiting, pruritus, addiction, respiratory depression, constipation, sphincter of Oddi
spasm, miosis (except meperidine mydriasis), additive CNS depression with other drugs.
Tolerance does not develop to miosis and constipation. Treat toxicity with naloxone (competitive
opioid receptor antagonist) and prevent relapse with naltrexone once detoxified.
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