MS-1415

A 32-year-old woman presents with a 14-day history of profuse, watery diarrhoea. She denies the presence of blood. There is no history of recent travel. The diarrhoea is stopping her from going to work, and so she has been forced to take unpaid leave. She wants to return to work as she is the sole breadwinner for the family.

On examination, she is apyrexial but looks clinically dehydrated.

After ruling out infection and inflammatory bowel disease, you prescribe a short course of loperamide to help slow down her bowel movements.

What is the mechanism of action of the prescribed anti-diarrhoeal medication?