All unresponsive to atropine and neostigmine

Discussion in 'USMLE STEP 1' started by Guest, Apr 12, 2011.

  1. Guest

    Guest Guest

    Hypotension, bradycardia, respiratory depression, and muscle weakness, all unresponsive to atropine and neostigmine, would most likely be due to which of the following?
    A. Diazoxide
    B. Isofluorphate
    C. Tubocurarine
    D. Nicotine
    E. Pilocarpine
  2. Guest

    Guest Guest

    The answer is: D

    Nicotine is a depolarizing ganglionic blocking agent that initially stimulates and then blocks nicotinic muscular (NM) (skeletal muscle) and nicotinic neural (NN) (parasympathetic ganglia) cholinergic receptors. Blockade of the sympathetic division of the autonomic nervous system (ANS) results in arteriolar vasodilation, bradycardia, and hypotension. Blockade at the neuromuscular junction leads to muscle weakness and respiratory depression caused by interference with the function of the diaphragm and intercostal muscles. Atropine, a muscarinic receptor blocker, would be an effective antagonist, as would neostigmine, a cholinesterase inhibitor. Pilocarpine and isofluorphate are cholinomimetics and can be antagonized by atropine; the effects of tubocurarine can be inhibited by neostigmine. Diazoxide, a vasodilator, would cause tachycardia, rather than bradycardia.

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