Atropine clinical selectivity

Atropine is highly selective for muscarinic receptors. Its potency at nicotinic receptors is much lower, and actions at nonmuscarinic receptors are generally undetectable clinically. 

Perhaps the most widely knowm agent to alter cholinergic transmission is the belladonna alkaloid, atropine. This agent is relatively selective for muscarinic receptors and as such decreases exocrine gland secretion, smooth muscle tone and the effects of vagal nerve stimulation of the heart. Atropine has several clinical applications including use as a preoperative medication, post-myocardial infarction to increase heart... 

Doxorubicin is a nonspecific inhibitor of topoiso-merase I and II. Topotecan and irinotecan selectively inhibit topoisomerase I, an enzyme required for DNA replication. These agents have clinical efficacy in relapsed ovarian and colorectal cancer, respectively. Dose limiting toxicity is bone marrow depression and, in the case of irinotecan, delayed diarrhoea. Administration of irinotecan may be complicated by an acute cholinergic reaction, reversible by administering atropine s.c. 

After the observation in healthy volunteers that intravenous atropine reduced the rate of TLESRs by nearly 60%, a study in GERD patients produced similar findings. Current evidence suggests a central site of action, because selective peripheral anticholinergic agents, which do not cross the blood-brain barrier, fail to inhibit TLESRs. It is, however, unlikely that anticholinergic agents will be clinically effective because of their deleterious effects on supine acid clearance and worrisome side-effect profile. 

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