Step 1: Understanding the Concept: Four laxatives need to be matched to their mechanism of action, so recall how each drug class works in the gut before looking at the answer choices.
Step 2: Key Formula or Approach: Group laxatives by mechanism: stimulant laxatives increase peristalsis through enteric nerves, osmotic laxatives pull water into the bowel, chloride channel activators increase fluid secretion into the bowel, and prokinetic agents stimulate motility receptors directly.
Step 3: Detailed Explanation: Senna stimulates enteric nerves to increase gut motility, which is the stimulant mechanism (Q). Lactulose is a non-absorbable sugar that draws water into the colon by osmosis, which is the osmotic mechanism (P). Lubiprostone activates chloride channels on the intestinal epithelium, pulling fluid into the bowel and softening stool, which is the chloride channel mechanism (R). Prucalopride is a selective 5-HT4 receptor agonist that directly stimulates colonic motility, which is the prokinetic mechanism (S). Putting these together gives Senna-Q, Lactulose-P, Lubiprostone-R, Prucalopride-S.
Step 4: Final Answer: The correct match is (1)-(Q), (2)-(P), (3)-(R), (4)-(S).
