Flashcards in Pharmacology VII Deck (25)
What is the mechanism of action of local anesthetics?
Blocks sodium channels by binding to specific receptors on the inner portion of the channel; preferential binding to activated sodium channels making the drug most effective in rapidly firing neurons (p.454)
How do tertiary amine local anesthetics penetrate membranes?
In uncharged form; they then bind to ion channels as charged form (p.454)
What types of drugs are given along with local anesthetics to enhance local action?
Vasoconstrictors (usually epinephrine) (p.454)
What effect do vasoconstrictors have when given along with local anesthetics?
Decrease bleeding, increase anesthesia, decrease systemic concentration (p.454)
How does the amount of anesthetic needed vary with acidity of the tissue?
In infected (acidic tissue), alkaline anesthetics are charged and cannot penetrate the membrane effectively thus more anesthetic is needed (p.454)
What is the order in which nerves are blockaded by local anesthetics?
Smal myelinated fibers> small unmyelinated fibers > large myelinated fibers > large unmyelinated fibers (p.454)
What is the order of sensation loss due to local anesthetic action?
1) pain; 2) temperature; 3) touch; 4) pressure (p.454)
What are local anesthetics used for?
Minor surgical procedures, spinal anesthesia (p.454)
What toxicities are associated with use of local anesthetics?
CNS excitation, hypertension, hypotension (p.454)
Name one toxicity specific to bupivacine when used as a local anesthetic.
Severe cardiovascular toxicity (p.454)
Name one toxicity specific to cocaine when used as a local anesthetic.
What are neuromuscular blocking drugs used for?
Muscle paralysis in surgery or mechanical ventillation (p.455)
For which receptors are neuromuscular blocking drugs selective?
Motor (vs autonomic) nicotinic receptors (p.455)
What are the two classes of neuromuscular blocking drugs?
Depolarizing and nondepolarizing drugs (p.455)
What is the mechanism of action of succinylcholine?
A depolarizing neuromuscular blocking drug; strong Ach receptor agonist that produces sustained depolarization and prevents muscle contraction (p.455)
Describe how neuromuscular blockade is reversed after use of depolarizing neuromuscular blocking drugs.
Phase I: no antidote; block is potentiated by cholinesterase inhibitors; Phase II: antidote consists of cholinesterase inhibitors (e.g. neostigmine) (p.455)
Describe the mechanisms of the two phases of neuromuscular blockade.
Phase I: prolonged depolarization; phase II: repolarized channels, but blocked thus Ach receptors are available but are desensitized (p.455)
What complications are associated with use of depolarizing neuromuscular drugs?
Hypercalcemia, hyperkalemia, malignant hyperthermia (p.455)
Name six nondepolarizing neuromuscular blocking drugs.
Tubocurarine, atracurium, mivacurium, pancuronium, vecuronium, rocuronium (p.455)
What is the mechanism of action of nondepolarizing neuromuscular blocking drugs?
Competitive antagonists that compete with Ach for receptors (p.455)
What drugs are used to reverse the blockade associated with nondepolarizing neuromuscular blocking drugs?
Neostigmine, edrophonium, other cholinesterase inhibitors (p.455)
What is the mechanism of action of dantroline?
Prevents the release of Ca2+ from the sarcoplasmic reticulum of skeletal muscle (p.455)
What is dantroline used for?
Treatment of malignant hyperthermia (due to inhalation anesthetics and succinylcholine); can also be used to treat neuroleptic malignant syndrome (p.455)
What is neuroleptic malignant syndrome?
A toxicity of antipsychotic drugs (p.455)