McKenna's Pharmacology for Nursing, 2e

924

P A R T 1 1  Drugs acting on the gastrointestinal system

Contraindications and cautions Antidiarrhoeal drugs should not be given to anyone with known allergy to the drug or any of its compo- nents to prevent hypersensitivity reactions . Caution should be used in pregnancy and breastfeeding because of the potential adverse effects to the fetus or baby . Care should also be taken in individuals with any history of GI obstruction, acute abdominal conditions, which could be exacerbated by the effects of the drugs, or diarrhoea due to poisonings, which could be worsened by slowing of the GI tract, allowing increased time for absorption of the poison; or with hepatic impairment, which could alter the metabolism of the drugs. Renal function should be monitored before starting treatment and during treatment (more frequent mon- itoring may be required in renal impairment); cardiac hypersensitivity reactions have been reported; caution is required if there is a previous history of myocarditis or pericarditis, irrespective of cause. Adverse effects The adverse effects associated with antidiarrhoeal drugs, such as constipation, distension, abdominal discomfort, nausea, vomiting, dry mouth and even toxic mega­ colon, are related to their effects on the GI tract. Other adverse effects that have been reported include fatigue, weakness, dizziness and skin rash. Opium derivatives are also associated with lightheadedness, sedation, THE SITUATION P.F. received an all-expenses-paid trip to Thailand to celebrate his graduation from university. He was very excited about getting away for a week of sun and fun, and arranged to stay in the same hotel as two college friends who were also celebrating. The three men had a wonderful time visiting the beaches, bars and nightclubs in the area. On the third day of the trip, P.F. began experiencing nausea, some vomiting and a low-grade fever. Several hours later he began experiencing intense cramping and diarrhoea. For the next 2 days, P.F. felt so ill he was unable to leave his hotel room. The next morning, he arranged for an emergency trip home. CRITICAL THINKING What is probably happening to P.F.? Think about the gastrointestinal reflexes and explain the underlying cause for his signs and symptoms.

euphoria, hallucinations and respiratory depression related to effect on the opioid receptors. Drug–drug interactions Drug interactions vary depending on the antidiarrhoeal agent. Consult the drug package insert for specific interactions. Prototype summary: Loperamide Indications: Control and symptomatic relief of acute, non-specific diarrhoea and chronic diarrhoea associated with irritable bowel syndrome; reduction of volume of discharge from ileostomies. Actions: Inhibits intestinal peristalsis through direct effects on the longitudinal and circular muscles of the intestinal wall, slowing motility and movement of water and electrolytes. Pharmacokinetics: Route Onset Peak Oral (capsule) Varies 5 hours T 1/2 : 10.8 hours; metabolised in the liver and excreted in urine and faeces.

Adverse effects: Abdominal pain, distension or discomfort; dry mouth; nausea; constipation; dizziness; tiredness; drowsiness.

CRITICAL THINKING SCENARIO Traveller’s diarrhoea

What treatment should be started now? What could have been done to prevent this problem from occurring? What possible drug therapy might have been helpful for P.F.? DISCUSSION P.F. is probably experiencing the common disorder called traveller’s diarrhoea. This disorder occurs when pathogens found in the food and water of a foreign environment are ingested. (Because these pathogens are commonly found in the environment, they do not normally cause problems for the people who live in the area.) When the pathogen, usually a strain of Escherichia coli , enters a host that is not accustomed to the bacteria, it releases enterotoxins and sets off an intestinal–intestinal reaction in the host. The intestinal–intestinal reaction results in a reduction of activity above the point of irritation (which causes