Drug Therapy and the Compromised Bowel
Several factors can alter the absorption of drugs taken orally in patients with a compromised digestive system. The most important determinations are the length of bowel available for drug absorption, and which section of the bowel has been removed. The small bowel, with its large surface area and high blood flow, is the most important site of drug absorption. Therefore, the larger the amount of the small bowel that has been removed, the higher the risk that drug absorption will be affected. Other factors such as the time it takes for food to empty from the gut (gastric emptying) and move along the intestinal tract (transit time) also come into play. Due to these factors, people with ileostomies are at higher risk for sub-optimal drug absorption than people with distal colostomies. People who have had sections of their small bowel removed and do not have an ostomy are also at higher risk.
In order to minimize problems with drug absorption, follow these general principles. For the ileostomy patient, dosage forms with quick dissolution (dissolving tablets) and absorption should be used. Liquids, gelatine capsules, and uncoated tablets are usually better and well absorbed. Dosage forms such as enteric coated and sustained release products should be avoided due to the possibility of poor absorption. Enteric coating is designed to prevent stomach lining irritation from direct contact with certain drugs, such as aspirin. Sustained release products are designed so that a small, sustained amount of medication is released along the small intestine over time.
These drugs include Demerol® (meperidine), Dilaudid® (hydromorphone), Talwin® (pentazocine), Percodan® (oxycodone), Percocet® (oxycodone), and Tylenol® 1, 2, 3, (containing codeine). All these drugs share the common property of slowing intestinal peristalsis (the muscle contractions of the bowels). Because of this action, narcotic analgesics may cause constipation. This effect is of special consideration for colostomy patients. Indeed, this action is often used to treat diarrhea.
Oral antibiotics may pose significant problems for patients with ostomies because they can change the normal good bacterial flora. Broad-spectrum antibiotics such as Amoxil® (amoxicillin trihydrate), Keflex® (cephalexin), Septra® (trimethoprim-sulfamethoxazole), and Cipro® (ciprofloxacin) kill bad bacteria but wipe out the good ones as well. The change in flora can sometimes lead to diarrhea and this can lead to electrolyte loss and dehydration causing distress for the patient. It is always a good idea to take probiotics (acidophilus) after finishing your course of antibiotics to replace some of the good bacteria.
The effect of antacids on the ostomy patient is dependent on the class of antacids and the type of ostomy.
Classification of antacids
- Calcium carbonate (Tums®)
- Aluminium hydroxide gels (Amphojel®)
- Magnesium/aluminium hydroxide combinations (Maalox®, Mylanta®, Riopan®)
Calcium-containing antacids can cause constipation and magnesium-containing antacids can cause diarrhea, especially in patients with ileostomies as they can cause osmotic diarrhea (drawing water into the intestines). The aluminium hydroxide gels are of particular concern in colostomy patients as they can cause constipation.
Thus, it can be seen that the antacid of choice for a patient with a compromised bowel is largely dependent on the type of bowel surgery. Patients who have excessive output problems while using magnesium/aluminium combinations may benefit by switching to aluminium hydroxide gel antacid. Conversely, patients with constipation secondary to aluminium hydroxide gel may benefit by switching to magnesium-containing products.
Aspirin and the Non-Steroidal Anti-Inflammatory Medications (Advil®, Motrin®, Naproxen® etc)
Anti-inflammatory drugs share the potential for gastric bleeding (bleeding in the stomach) and irritation. These drugs should be taken with food to minimize the risk. Fecal output should be monitored for traces of blood or black tarry stools, which may indicate gastric bleeding and should be brought to the attention of your doctor.
In order to minimize problems with drug absorption, follow several general principles. For the ileostomy patient, dosage forms with quick dissolution (dissolving tablets) and absorption should be used. Liquids, gelatine capsules, and uncoated tablets are usually better and well absorbed. Dosage forms such as enteric coated and sustained release products should be avoided due to the possibility of poor absorption. Enteric coating is designed to prevent stomach-lining irritation from direct contact with certain drugs, such as aspirin. Sustained release products are designed so that a small, sustained amount of medication is released along the small intestine over time.
These are drugs widely used to treat hypertension (high blood pressure) and congestive heart failure by decreasing the fluid load on the heart. Colostomy patients can use diuretics without much ill effect. However patients with a urostomy may experience increased urine flow, especially with drugs like Lasix® (furosemide) and Zaroxolyn® (metolazone). Because of the increased urine output, the appliance will need to be emptied more frequently. As for ileostomates, diuretics should be used with caution. Maintaining electrolytes and fluid balance even in the absence of diuretics is difficult. The addition of diuretics can cause dehydration and severe electrolyte imbalance.
Often, when a doctor prescribes a diuretic, a prescription for potassium and sodium supplements is also given to keep the electrolytes in check. Potassium supplements are available in liquid, powder and extended release tablet preparations. It is advisable to split the daily potassium intake or take sustained release preparations, as taking all the potassium at once in the ileostomate can cause what is known as osmotic diarrhea (water drawn into the gut). Examples of sustained release preparations are Slow-K®, Apo-K®, and Micro-K Extencaps® to name a few. Good food sources of potassium are bananas, tomatoes, and oranges.
As mentioned in the last newsletter, narcotics (Tylenol®3, codeine, etc) all have the ability to slow the bowels and provide relief of loose stools and excessive ostomy output. The most frequently used agents are Imodium (loperamide) – available over the counter, and Lomotil® (diphenoxylate/atropine) – available by prescription. These drugs are safe and effective if used appropriately). Other over the counter products that may also be effective in controlling diarrhea include Kaopectate® (attapulgite and pectin) and Pepto-Bismol® (bismuth compound). These agents help to add form to the stool and are generally well tolerated. Psyllium (Metamucil®, Prodiem® Plain) in small doses may also be effective in adding bulk to the stool for the colostomy or ileostomy patient with chronic loose stools.
Laxatives can have one of two effects on the ostomy patient, depending on the type of ostomy and type of laxative. Laxatives can be classified according to their action. There are bulk forming laxatives (bran, psyllium), lubricant laxatives (mineral oil), osmotic agents that draw water into the gut (milk of magnesia, phospho soda) and stimulant laxatives (cascara, senna, and castor oil). Laxatives should be used with caution in the ileostomate because of potential for severe dehydration and electrolyte loss.
Although laxatives can be used in colostomates, harsher laxatives (stimulants) should also be used with caution, if at all. You may get more benefit from bulk forming laxatives, which aid in the formation of solid stool and may promote regularity. Use Stool softeners (docusate sodium) to help with problems of constipation.
As laxatives are frequently used in pre-diagnostic pre-operative protocols, it is important that the ostomy patient remind their healthcare practitioner of the type of ostomy they have, so a suitable protocol may be chosen.
Patients who have an ostomy, or otherwise compromised bowel, should always consult their healthcare practitioners to see if a medication may have an adverse effect on their unique digestive system. The general principle applies that any drug with the potential to alter gastrointestinal function in patients would be more likely to cause problems in the ostomy patient.
Adil Saleh, BSc (Pharm.) D. RPh
First published in The Inside Tract® Newsletter Issues 128 & 129