Home Books Katzung & Trevor's Pharmacology: Examination & Board Review, 12e

Chapter 8: Cholinoceptor Blockers & Cholinesterase Regenerators

A 27-year old compulsive drug user injected a drug he thought was methamphetamine, but he has not developed any signs of methamphetamine action. He has been admitted to the emergency department and antimuscarinic drug overdose is suspected. Probable signs of atropine overdose include which one of the following?

(A) Gastrointestinal smooth muscle cramping

(B) Increased heart rate

(C) Increased gastric secretion

(D) Pupillary constriction

(E) Urinary frequency

Tachycardia is a characteristic atropine overdose effect. Bradycardia is sometimes observed after small doses. None of the other choices are typical of atropine or methamphetamine overdose. The answer is B.

Which of the following is the most dangerous effect of belladonna alkaloids in infants and toddlers?

(A) Dehydration

(B) Hallucinations

(C) Hypertension

(D) Hyperthermia

(E) Intraventricular heart block

Choices B, D, and E are all possible effects of the atropine group. In infants, however, the most dangerous effect is hyperthermia. Deaths with body temperatures in excess of 42 °C have occurred after the use of atropine-containing eye drops in children. The answer is D.

Which one of the following can be blocked by atropine?

(A) Decreased blood pressure caused by hexamethonium

(B) Increased blood pressure caused by nicotine

(C) Increased skeletal muscle strength caused by neostigmine

(D) Tachycardia caused by exercise

(E) Sweating caused by exercise

Atropine blocks muscarinic receptors and inhibits parasympathomimetic effects. Nicotine can induce both parasympathomimetic and sympathomimetic effects by virtue of its ganglion-stimulating action. Hypertension and exercise-induced tachycardia reflect sympathetic discharge with norepinephrine release and therefore would not be blocked by atropine. Exercise-induced sweating is another sympathomimetic response, but it is mediated by acetylcholine released from sympathetic nerve fibers at eccrine sweat glands. The answer is E.

Two new synthetic drugs (X and Y) are to be studied for their cardiovascular effects. The drugs are given to three anesthetized animals while the blood pressure is recorded. The first animal has received no pretreatment (control), the second has received an effective dose of a long-acting ganglion blocker, and the third has received an effective dose of a long-acting muscarinic antagonist.

Drug X caused a 50 mm Hg rise in mean blood pressure in the control animal, no blood pressure change in the ganglion-blocked animal, and a 75 mm mean blood pressure rise in the atropine-pretreated animal. Drug X is probably a drug similar to

(A) Acetylcholine

(B) Atropine

(C) Epinephrine

(D) Hexamethonium

(E) Nicotine

Drug X causes an increase in blood pressure that is blocked by a ganglion blocker but not by a muscarinic blocker. The pressor response is actually increased by pretreatment with atropine, a muscarinic blocker, suggesting that compensatory vagal discharge might have blunted the full response. This description fits a ganglion stimulant like nicotine but not epinephrine, since epinephrine’s pressor effects are produced at α receptors, not in the ganglia. The answer is E.

The net changes in heart rate induced by drug Y in these experiments are shown in the following graph.

Drug Y is probably a drug similar to

(A) Acetylcholine

(B) Edrophonium

(C) Hexamethonium

(D) Nicotine

(E) Pralidoxime

Drug Y causes an increase in heart rate that is blocked by a muscarinic blocker but reversed by a ganglion blocker. The fact that a ganglion blocker reverses the unknown drug’s effect suggests that the control response (tachycardia) involves the baroreceptor reflex. The description fits a direct-acting muscarinic stimulant such as acetylcholine (given in a dosage that causes a significant drop in blood pressure). An indirect-acting cholinomimetic (cholinesterase inhibitor, B) would not produce this pattern because the vascular muscarinic receptors involved in the depressor response are not innervated and are unresponsive to indirectly acting agents. The answer is A.

A 30-year-old man has been treated with several autonomic drugs for 4 weeks. He is now admitted to the emergency department showing signs of drug toxicity. Which of the following signs would distinguish between an overdose of a ganglion blocker versus a muscarinic blocker?

(A) Cycloplegia

(B) Dry skin in a warm environment

(C) Miosis

(D) Postural hypotension

(E) Tachycardia

Neither ganglion blockers nor muscarinic blockers cause miosis; they cause mydriasis. Both classes of cholinoceptor blockers increase resting heart rate and cause cycloplegia, because these are determined largely by parasympathetic tone. Similarly, both can cause dry skin, since this requires cholinergic transmission. Postural hypotension, on the other hand, is a sign of sympathetic blockade, which would occur with ganglion blockers but not muscarinic blockers (Chapter 6). The answer is D.

Which of the following is an accepted therapeutic indication for the use of antimuscarinic drugs?

(A) Atrial fibrillation

(B) Botulinum poisoning

(C) Chronic obstructive pulmonary disease (COPD)

(D) Glaucoma

(E) Postoperative urinary retention

Atrial fibrillation and other arrhythmias are not responsive to antimuscarinic agents. Botulinum poisoning is associated with parasympathetic blockade. Antimuscarinic drugs tend to cause urinary retention and may precipitate or exacerbate glaucoma. Bronchospasm is mediated in part by vagal outflow in many patients with COPD and in some with asthma. The answer is C.

Which of the following is an expected effect of a therapeutic dose of an antimuscarinic drug?

(A) Decreased cAMP (cyclic adenosine monophosphate) in cardiac muscle

(B) Decreased DAG (diacylglycerol) in salivary gland tissue

(C) Increased IP₃ (inositol trisphosphate) in intestinal smooth muscle

(D) Increased potassium efflux from smooth muscle

(E) Increased sodium influx into the skeletal muscle end plate

Muscarinic M₁ and M₃ receptors mediate increases in IP₃ and DAG in target tissues (intestine, salivary glands). M₂ receptors (heart) mediate a decrease in cAMP and an increase in potassium permeability. Antimuscarinic agents block these effects. The answer is B.

Which one of the following drugs causes vasodilation that can be blocked by atropine?

(A) Benztropine

(B) Bethanechol

(C) Botulinum toxin

(D) Cyclopentolate

(E) Edrophonium

(F) Neostigmine

(G) Pralidoxime

Bethanechol (Chapter 7) causes vasodilation by directly activating muscarinic receptors on the endothelium of blood vessels. This effect can be blocked by atropine. Indirectly acting agents (AChE inhibitors) do not typically cause vasodilation because the endothelial receptors are not innervated and endogenous acetylcholine is not released at this site. Pralidoxime is a distracter in this answer list. The answer is B.

Which one of the following drugs has a very high affinity for the phosphorus atom in parathion and is often used to treat life-threatening insecticide toxicity?

(A) Atropine

(B) Benztropine

(C) Bethanechol

(D) Botulinum

(E) Cyclopentolate

(F) Neostigmine

(G) Pralidoxime

Pralidoxime has a very high affinity for the phosphorus atom in organophosphate insecticides. The answer is G.

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Chapter 8: Cholinoceptor Blockers & Cholinesterase Regenerators

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