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Loperamide crystals

Annie Cavanagh and David McCarthy

Loperamide crystals

Download this image from Wellcome Collection.

This false-coloured scanning electron micrograph shows loperamide crystals. Loperamide, an antimotility drug used to treat diarrhoea, works by slowing down the movement of the intestine and reducing the speed at which the contents of the gut pass through. Food remains in the intestines for longer and water can be more effectively absorbed back into the body. This results in firmer stools that are passed less often. The crystal group measures approximately 250 microns across.

What is the drug's mechanism of action?

Loperamide is an opioid receptor agonist and acts on the mu-opioid receptors in the myenteric plexus, a network of nerve fibres in the muscular coat of the large intestine. Loperamide decreases the activity of the myenteric plexus, which acts like morphine to decrease the tone (muscle tension) of longitudinal smooth muscle but increase the tone of the circular smooth muscle of the intestinal wall. This increases the length of time that food stays in the intestine, allowing more water to be absorbed from the faecal matter into the body. Loperamide also decreases colonic mass movements and suppresses the gastrocolic reflex.

How were the crystals formed?

These crystals were re-crystallised from a pure laboratory sample. Annie used varying percentages of solvents to create the crystals and left them for two weeks before they were imaged. Slightly raised from the surface, this group formed in a very three-dimensional manner.