After a patient has had ostomy surgery certain drugs may affect them in ways different to pre-stoma. One of the differences is that drugs may now discolour stool or cause unsual odours. This will be more obvious to a stoma patient whose waste is collected in a bag, so explaining these changes to a patient that these changes may occur will stop unnecessary worrying.

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The following changes may occur:

• Iron supplements - dark green/black stool.

• Chlorophyll - Green stool 

• Activated charcoal - Black stool

• Chlorzoxazone - Orange or red stool

• Pepto-Bismol - Dark stool

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When a colostomy or ileostomy is formed the transit time through the small intestine may be altered due to the reduced length. Shortened intestinal length can have a significant effect on the pharmacokinetics and bioavailabilty of medications, so drug prescribing can be a concern for stoma patients. In some extreme cases whole undissolved can be found in a stoma bag. Medication that is coated, or designed to be slow release may not be absorbed at all, so it is not recommended.  

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Most drug absorption occurs in the upper small intestine, where the long villi give an increased surface area. After ostomy surgery many of the factors that have a profound influence on drug absorption have the potention to be altered. The main factors for the following.

• Reduced intestinal length - This is the most significant influence as it will decrease the surface area of the lumen.

• Mucosal integrity of the remaining bowel - Diseases that indicate a stoma, such as crohns can lead to impaired bowel function. This can include inflammation and strictures

• Gastric empyting, intestinal transit, motility and concomitant use of anti-motility drugs.

• pH of gastric and intestinal lumen.

• Drug formulation - Slow release forms of drugs are in general contraindicted in patients with a stoma as they do not dissolve rapidly enough.

• Drug dose .