Codeine antidiarrheal activity

The antidiarrheal activity of codeine results from two actions. First, there is a decrease in the propulsive contractile activity of the small and large intestines, which delays the forward movement of the contents of the intestines. Second, codeine causes an increase in the absorption of water from the intestinal contents. These gastrointestinal effects are mediated by specific opioid receptors in the gut (as we will see in... 

Antidiarrheal medications that reduce GI motility, such as loperamide, diphenoxylate/atropine, or codeine should be avoided in patients with active IBD due to the risk of precipitating acute colonic dilation (toxic megacolon). 

Kappa receptor activation does not appear to be responsible for dependence, euphoria, or effects on smooth muscle. Increases in cerebral blood flow and (possibly) increased intracranial pressure result from the respiratory depressant actions of opioid analgesics. The latter effects are due to increased arterial PrOj, which results from mu receptor inhibition of the medullary respiratory center. However, the activation of kappa receptors contributes to analgesia at the spinal level and is probably responsible for sedative actions of the opioids. The answer is (D). Codeine and possibly nalbuphine could decrease gastrointestinal peristalsis but not without marked side effects (and a prescription). Dextromethorphan is a cough suppressant. The other two drugs listed are opioids with antidiarrheal actions. Diphenoxylate is not available over-the-counter since it is a constituent of a proprietary combination that includes atropine sulfate (Lomotil). Loperamide is available over-the-counter. The answer is (D). 

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