msyamp
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The reflex change in heart rate in response to intravenous isoproterenol would be enhanced by which of the
following drugs?
A. Dobutamine
B. Esmolol
C. Hexamethonium
D. Phenylephrine
E. Pirenzepine
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| ssrpk
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Dobutamine
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| mjl1717
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Theory: Isopro is B1 and B2/Dobutamine is B1>B2 B1 is mostly heart and increase renin! beta is easily agonized at low doses! Pirenzepine is a M1 agonist used in PUD with a ganglionic block useful in inhibiting relaxation of the LES
Edited by mjl1717 on 01/02/06 - 03:35 PM
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| vamsi2004
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pirenzepine is a muscarininc antagonist (not agonist). wats the answer for the ques?????
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| Dragonfly
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A.
well since it asks for "REFLEX" change in the heart rate :
Isoprterenolol is B-specific( B1&B2). it stim. B2 on the vessel wall --> vasodilation --> reflex tachcardia (in addition to the direct tachycardia b/c of B1 effect)
Dobutamine is B1-specific --> further more tachycardia
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| vamsi2004
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but pirenzepine also causes tachycardia..
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| docsrinu
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can anyone post the ans?
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| fox
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what about phenylepherine? It also causes tachycardia.
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| giovanni83
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reflex change is bradycardia!
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| young_doc
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Pirenzepine does cause tachycardia, but NOT by stimulating B1, it does so by inhibiting M. We have to be careful in answering the question. We're asked which drug causes Tachycardia the same way as Isoproterenol.
Phenylephrine causes vasoconstriction, hence reflex Bradycardia. (though in high doses or in kids it can cause a paradoxycal tachycardia...)
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| docarchana
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thanku y_d for a gud explanation . so the ans is A.
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