Drugs Acting on the Intestines

WIKIDRUGS GASTROINTESTINAL DRUGS

Drugs Increasing Smooth Muscle Contractility

These drugs are used for conditions that are associated with hypomotility, such as megacolon, oesophageal reflux, atony and ileus.

Drugs Acting on 5-HT₄ Receptors

• An examples is metoclopramide that is an agonist at serotonin and dopamine receptors, this results in an increased release of acetylcholine and so increases gut motility.

Muscarinic Receptor Agonists

• Examples are carbachol and bethanecol. They should be used with slight caution as their resultant contractions can be painful.

Laxatives and Purgatives

These drugs should mainly be used to treat constipation, but bulk luxatives can be used to help control diarrhoea.

Lubricant Laxatives An example is liquid paraffin that is given orally. They supposedly coat and lubricate the contents of the gastrointestinal tract and help soften the faeces, thus making them easier to pass. The use of liquid paraffin is under debated between some clinicians as some feel that it works just as well as water, but has the added risk of causing a very serious pneumonia if the paraffin enters the trachea. On the other hand most equine vets in practice feel that it is a useful tool to help resolve impaction colics.

Bulk Laxatives Examples are bran, ispaghula and stericula, and they are administered orally. They work by absorbing water and so swell, this stimulates stretch receptors in th gastrointestinal tract and waves of peristalsis are stimulated. They are usedful in controlling diarrhoea because of their absorbant properties.

NB Never use in dehydrated animals as animals will loose water when these laxatives are in use. Please remember to offer the animal plenty of drinking water.

Osmotic Laxatives An example is lactulose, which is given orally. It works by drawing water into the intestinal lumen, this stretches the intestinal walls resulting in increased peristaltic waves.

NB Never use in dehydrated animals as animals will loose water when these laxatives are in use. Please remember to offer the animal plenty of drinking water.

Stimulant Laxatives An example is bisacodyl and is given orally. This works by having an irritant effect on the intestinal mucosa. This stimulates enteric nerves, resulting in increased peristalsis and increased water and electrolyte secretion into the lumen.

Enemas This is where warm water and mineral oil or sodium citrate are administered into the rectum and lower bowels of an animal. This helps evacuate the bowels of an animal before radiographs or surgery.