Laxatives and antidiarrhoeal agents

At a glance

• Laxatives work by holding water in the lumen (osmotic, bulk), stimulating the enteric nervous system (senna, bisacodyl), driving chloride secretion (linaclotide), speeding colonic motility (prucalopride) or blocking gut mu-opioid receptors (PAMORAs).
• Antidiarrhoeals act on mu receptors (loperamide), somatostatin receptors (octreotide) or bind a luminal secretagogue (bile acid sequestrants).
• Paper 1 uses this pharmacology to explain clinical findings: the stool osmotic gap, ammonia trapping by lactulose, hyponatraemia after bowel prep and cardiotoxicity from loperamide misuse.