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37 Cards in this Set
- Front
- Back
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How do indirectly acting cholinomimetics work?
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Indirect cholinomimetics work by inhibiting the acetylcholineserase enzyme.
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Explain the enzymatic hydrolysis of acetylcholine (three steps).
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(1) Binding of positively charged ammonium hed of acetylcholine at the anionic site and the carbonyl head at the esteratic site
(2) Hydrolysis - freeing the choline and momentarily acetylating he enzyme. (3) Acetate residue is hydrolyzed, leaving the free enzyme active site and acetic acid. |
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How do drugs inhibit Acetylcholinesterase?
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Drugs inhibit acetylcholinesterase by carbomylating the site thus slowing down the enzme's ability (Carbamylated estartic is more resistant to hydrolysis than it's corresoponding acetylated site). The enzyme cannot work again until the carbomylating site is removed.
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Name three reversible cholinesterase-inhibiing drugs.
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(1) Edrophonium
(2) Neostigmine (3) Physostigmine. |
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Explain Edrophonium.
Can it carbomylate? How long does it last? How is the drug used? |
- Edrophonium cannot carbomylate, instead it is statically attracted to the acetylcholinesterase.
- It is a short acting indirect cholinesterase - only lasting 15 minutes - the drug is used to diagnose patients with Myasthenia gravis (those with diminished nicotinic receptors). |
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Neostigmine:
What is the structure? Where is it able to go? What is its duration? What are its uses? |
- Neostigmine is a quaternary amine (similar to edrophonium)
- Neostigmine cannot enter the CNS. - The duration is 0.5 -2.5 hours. - (1) It is an antidote to antropine (2) Used topically to treat glaucoma (3) Txt of Myasthenia Gravis. |
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Physostigmine: - What are it's uses?
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(1) It is an antidote to antropine (2) Used topically to treat glaucoma and (3) Can be used to treat Alzheimer's because it can get into the CNS.
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What is an irreversible cholinesterase inhibitor?
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Irreversible cholinesterase inhibitors mostly consist of organophosphates. The phosphorylated esteratic site is extremely stable and resists hydrolysis. In fact, the recovery of AcE actvity is dependent on the synthesis of new enzymes.
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What is "aging?"
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"Aging" is the process of organophosphates where the alkylphosphate loses an alkyl group and the resulting monoalkylphosphate becomes even more tightly bound to the esteratic site.
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Which enzymes do irreversible cholinesterase inhibitors act on?
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Both the acetylcholinesterase and plasma cholinesterase.
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Which two irreversible agents are safely used to treat glaucoma?
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(1) Diisopropylfluorophosphate (DFP)
(2) Echothiophate NOTE: Echothiophate is not readily absorbed which is an advantage because otherwise it would be quite toxic. |
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What is Malathion?
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Malathion is a poisonous organic phosphate that acts as an irreversible cholinergic agent. Malathion is not metabolized by insects and fish but is by humans at least at low doses.
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What is Sarin Gas? Is it a drug?
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Sarin gas is an irreversible cholinergic inhibitor in the form of an organophosphate. Sarin Gas is the prototype of military "nerve gas" and can produce incapacitation or death in a few minutes after exposure to the skin or after inhalation. It can cross the BBB and can cause central and peripheral inhibition of AchE.
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What are some possible toxicities of organophosphates?
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(1) CNS: uneasiness and restlessness followed by depression.
(2) Eye: miosis and cycloplegia (3) Respiratory system: increased nasal and bronchial secretions and bronchial constriction. (4) SLUD (5) Skeletal Muscle Twitching |
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If someon were to face toxcities related to organophosphates what would be the drug used to treat patient nad how does the drug work?
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The drug of choice would be PRALIDOXIME. Pralidoxime does not cross the BBB and only works at the neuromuscular junction and does so by preventing "aging."
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Besides pralidoxime, what are other drugs given to someone facing organophosphate toxicities?
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Atropine is also given and works by blocking muscarinic and central effects.
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What are the three categories of drugs to consider for Cholinergic Blocking Drugs or Antagonist?
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(1) Muscarinic Blocking Drugs
(2) Neuromuscular Blockers (3) Ganglionic Blockers |
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What is the prototypical Muscarinic receptor antagonist?
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Atropine.
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What are possible toxicities from muscarinic receptor antagonists?
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Dry Mouth, constipation, decreased sweating, mydriasis, urinary retention, tachycardia, decreased lacrimation, precipitation of glaucoma, decreased respiratory secretions with increased susceptibility to respiratory ifection.
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In dentistry, what would atropine be given for?
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(1) To decrease salivation
(2) Drugs used before General Anesthesia because while under GA, one has increased glandular secretions. So if patient’s pulse goes up you can stop giving the drug because you know that the mouth should already be getting dry because the Tachycardia starts after the dry mouth. |
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What are the five muscarinic blocking drugs?
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Atropine, homatropine, tropicamide, ipratropium, cyclopentadine
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What are some possible uses for atropine in the eye?
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(1) Atropine acts by blocking contractions of iris circular muscle to produce mydriasis and blocking contraction of ciliary muscle to produce cycloplegia (inability for the lens to change shape).
Should not be given to pts with narrow-angle glaucoma (mydriasis can impede outflow of aqeous humor) |
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What are some possible uses for atropine in the GI tract?
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In the GI tract, atropine reduces both secretions and motility. It delays transit through the digestive system.
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Can atropine affect blood pressure?
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NO - at least not mst blood vessles because most blood vessels are not parasympathetically innervated. BUT
(1) can produce dilation of blood vessels in the facial blush area to induce a transient "atropine flush" (2) Atropine can induce mild tachycardia (3) Atropine can readily antagonize the vasodilation and hypotension induced by cholinergic vessels. |
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What is scopolamine?
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Scopolaimine is a muscarinic antagonist used to treat motion sickness.
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How do we treat Parkinson's Disease?
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By administering a muscarinic blocking drug to block the overwhelming and compensatory actions of acetylcholine.
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Can muscarinic blocking agents be used to treat Menstrual cramps?
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Yes, because it stops smooth muscle contraction.
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How can muscarinic blocking agents be used in an eye exam?
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Muscarinic blocking agents cause mydriasis - which is useful in an eye exam.
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Which Muscarinic Blocking agent can be used to treat asthma?
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Ipratropium is used in a nebulizer form for treating asthma.
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Explain the mechanism of Nicotine.
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Nicotine is a ganglionic blocking drog which initially activates the receptor to cause depolarization of the neuronal membrane. Because the membrane stays in a depoarized state, it no longer responds to Ach released from the pre-synaptic terminal.
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What is Verenicline (Chantix) used for?
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Chantix is a partial nicotinic agonist used to stop smoking but unfortunately this an cause suicidal thoughts.
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What is the mechanism of trimethaphan?
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Trimethaphan blocks the ganglionic nicotinic receptors by competing with Ach for the nicotinic receptor.
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What is an example of using trimethaphan?
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When dissecting the aortic aneurysm, the heart's natural reaction after losing a lot of blood is to beat faster - tachycardia. By using trimethaphan, the heart will not react this way because it blocks ganglionic niicotinic receptors.
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Describe Curare.
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Curare is a competetive or nondepolarizing reversible drug used at the neuromuscular junction. It binds to nicotinic receptors and causes skeletal muscle relaxation.
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Why is Vecuronium so useful?
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Vecuronium is a drug also used as a competitive reversible nueromuscular blocking agent. However, instead of triggering a histamic response, vecuronium does not. This is especially useful for patients with asthma.
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What is succinylcholine?
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Succinylcholine is a nueromuscular blocking agent. It is an non-competitive or depolarizing drug. It acts by producing a persistent depolarization of the motor end plate. When the motor endplate is depolarized, it is not reescitable.
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What are some specific examples of when succinylcholine is used?
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(1) Incubation
(2) Resetting bone fractures (3) During surgery to relax skeletal muscle (4) For pt's receiving electroshock therapy |
