Which statement about laxatives is false?

• A. Phenolphthalein, a diphenylamine derivative just like Bisacodyl, was removed from the market due to the possibility of cardiac toxicity
• B. Stool softeners or stool surfactant agents include Docusate and Glycerin suppository
• C. Osmotic laxatives are indigestible and hydrophilic colloids that absorb water, forming a bulky, emollient gel that distends the colon and promotes peristalsis
• D. Chronic use of stimulant laxatives such as aloe, senna, and cascara can lead to a characteristic brown pigmentation of the colon known as "melanosis coli."

Answer: (C)

The key idea here is matching laxative type to its mechanism. Osmotic laxatives work by creating an osmotic pull in the intestinal lumen, drawing water into the stool to soften it and increase its volume without needing to form a gel. They include agents like lactulose, sorbitol, magnesium salts, and polyethylene glycol. The statement in question, however, describes laxatives as indigestible hydrophilic colloids that absorb water to form a bulky, emollient gel that distends the colon and promotes peristalsis. That description fits bulk-forming laxatives (fiber-like agents such as psyllium and methylcellulose) rather than osmotic laxatives. So labeling this mechanism as osmotic is incorrect, making the statement false.

For context, the other points are accurate: phenolphthalein was removed from use due to concerns about cardiac toxicity (and cancer risk). Stool softeners like docusate are designed to soften stool, and glycerin suppositories act to ease stool passage (often by local osmotic effects). Long-term use of stimulant laxatives (like aloe, senna, cascara) can lead to melanosis coli, a brown pigmentation of the colon.

The essential lesson is to keep straight which laxatives work by osmosis to draw water in versus which fibers swell with water to form a bulky stool, and to connect that difference to the clinical statement.