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
(C) Increased gastric secretion
(D) Pupillary constriction
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?
(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.