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Anticholinesterases
Pharm - Fundamentals
18
Medical
Graduate
08/25/2012

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Term
Forms of acetyl cholinesterase
Definition
Brain: catalytic subunits bound to membrane anchoring protein
Muscle: tetramers of catalytic subunits linked via long, collagen-like tails that are anchored to the basement membrane
Plasma: 'psuedo' cholinesterase which cleave a variety of esters and are active towards butyrylcholine (not used as a drug) (note that RBCs contain 'true' AChE)
Term
Reversible anti-AChE
Definition
Quaternary amine: Simple competitive inhibitor
Edrophonium
Carbamates: competitive inhibitors that undergo slow hydrolysis
Physostigmine
Neostigmine
Pyridostigmine
Term
Edrophonium
Definition
Quaternary amine with brief duration (1-5 mins). Used to test for myasthenia gravis where IV administration causes a brief improvement of strength. Also used to judge correct dosage: if brief improvement is seen with use that patient may benefit from a higher dose of carbamate.
Term
Physostigmine
Definition
Crosses BBB into CNS, used for treatment of wide-angle glaucoma, often with pilocarpine. Used to treat atropine overdose ('PHYxes' atropine overdose). Can adversely facilitate formation of cataracts.
Term
Neostigmine
Definition
Short lasting (0.5 - 2hr). Used to treat loss of tone in GI tract and bladder (urinary retention) either from disease or from postoperative recovery from anesthesia. Also used for myasthenia gravis. No CNS penetration ('NEO' CNS penetration).
Term
Pyridostigmine
Definition
Used to treat myasthenia gravis, longer duration (3-6hr) than neostigmine.
Term
Ambenonium
Definition
Similar to pyridostigmine but even longer acting (4-8hr).
Term
Irreversible AChE inhibitors
Definition
Also termed organophosphates, form highly stable (covalent) phospho-intermediates. Take up to hundreds of hours to be cleaved off of enzyme. Before 'aging' is sensitive to nucleophilic attack by an oxime such as pralidoxime. After 'aging' is no longer susceptible.
Term
Echothiophate
Definition
Used to treat glaucoma (third-line), only clinically useful organophosphate.
Term
Malathion
Parathion
Definition
Insecticides responsible for many cases of farm poisonings. Converted to malaoxon and paraoxon, respectively, which are more toxic compounds. Detoxified in mammals and birds via plasmaesterases.
Term
Sarin/Soman
Definition
'Nerve gases' that are potent inhibitors of AChE, among the most toxic agents known.
Term
Donepezil
Definition
Used in treatment of Alzheimer's. Long acting (once-a-day dosing), CNS penetrant, good oral absorption.
Term
Rivastigmine
Definition
Carbamate similar to physostigmine used to treat Alzheimer's. Requires twice-a-day dosing.
Term
Galantamine
Definition
Long-acting drug for Alzheimer's. Not only a AChE-I but also a potent allosteric enhancer of CNS nicotinic receptors.
Term
AChE inhibitor toxicity and symptoms
Definition
Mixture of muscarinic, nicotinic and CNS effects. 'SLUDGE-BAM': salivation, lacrimation, urination, defecation, GI upset, emesis, bradycardia, bronchoconstriction, bowel movement, abdominal cramps, anorexia, miosis. (Also DDUMBBELSS)
Term
Organosphophates vs. Carbamates
Definition
Organophosphates are longer-lasting and tend to have nicotinic excess symptoms, whereas carbamates tend to have more muscarinic symptoms.
Term
Mechanism of lethal AChE-I overdose
Definition
Death is usually from respiratory failure due to bronchoconstriction, bronchorrhea (high volumes of sputum production), central respiratory distress, and weakness or paralysis of respiratory muscles.
Term
Treatment of AChE-I poisoning
Definition
Mixture of atropine (muscarinic blocker) and pralidoxime (regenerator of un-'aged' enzyme), with diazepam to prevent convulsions.
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