McKenna's Pharmacology for Nursing, 2e

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C H A P T E R 5 7 Drugs affecting gastrointestinal secretions

TABLE 57.1

DRUGS IN FOCUS Drugs used to treat gastro-oesophageal reflux disease and ulcer disease (continued)

Drug name

Dosage/route

Usual indications

GI protectant

1 g PO b.d to q.i.d.

Short-term treatment of duodenal ulcers; maintenance of duodenal ulcers (at reduced dose) after healing in adults; treatment of oral and oesophageal ulcers due to radiation, chemotherapy or sclerotherapy; currently under investigation for treatment of gastric ulcers, gastric damage induced by non-steroidal antiinflammatory drugs (NSAIDs), prevention of stress ulcers in acutely ill individuals Prevention of NSAID-induced ulcers in adults at high risk for development of these gastric ulcers; under investigation for treatment of duodenal ulcers in people who are not responsive to H 2 antagonists; used in combination therapy with mifepristone as an abortifacient

sucralfate (Carafate, Ulcyte)

Prostaglandin

200 mcg PO q.i.d.; reduce dose in people with renal impairment

misoprostol (Cytotec)

• Prophylaxis of stress-induced ulcers and acute upper GI bleeding in critical people (blocking the production of acid protects the stomach lining, which is at risk because of decreased mucus production associated with extreme stress). • Treatment of erosive gastro-oesophageal reflux (decreasing the acid being regurgitated into the oesophagus will promote healing and decrease pain). • Relief of symptoms of heartburn, acid indigestion and dyspepsia. See the Critical thinking scenario for additional infor- mation on H 2 antagonists. Pharmacokinetics Ranitidine is available in oral and parenteral forms. Nizatidine, cimetidine and famotidine are available only in oral form. Cimetidine was the first drug in this class to be developed. It has been associated with antiandrogenic effects, including gynaecomastia and galactorrhoea. It reaches peak levels in 1 to 1.5 hours and is metabolised mainly in the liver; it can slow the metabolism of many other drugs that use the same metabolising enzyme system. It is excreted in urine. It has a half-life of 2 hours and is known to cross the placenta and enter breast milk. Ranitidine, which is longer acting and more potent than cimetidine, is not associated with the antian- drogenic adverse effects or the marked slowing of metabolism in the liver as cimetidine is. It reaches peak levels in 5 to 15 minutes when given parenterally and 1 to 3 hours when given orally. It has a duration of 8 to 12 hours and a half-life of 2 to 3 hours. Ranitidine is metabolised by the liver and excreted in urine. It crosses the placenta and enters breast milk.

Famotidine is similar to ranitidine, but it is much more potent than either cimetidine or ranitidine. It reaches peak effects in 1 to 3 hours and has a duration of 6 to 15 hours. Famotidine is metabolised in the liver and excreted in urine with a half-life of 2.5 to 3.5 hours. Famotidine crosses the placenta and enters breast milk. Nizatidine, the newest drug in this class, is similar to ranitidine in its effectiveness and adverse effects. It differs from the other three drugs in that it is eliminated by the kidneys, with no first-pass metabolism in the liver. It is the drug of choice for people with liver dysfunction and for those who are taking other drugs whose metab- olism is slowed by the hepatic activity of the other three H 2 antagonists. It reaches peak effects in 0.5 to 3 hours and has a half-life of 1 to 2 hours. Like the other three drugs, it crosses the placenta and enters the breast milk. Contraindications and cautions The H 2 antagonists should not be used with known allergy to any drugs of this class to prevent hyper- sensitivity reactions . Caution should be used during pregnancy or breastfeeding because of the potential for adverse effects on the fetus or breastfeeding infant and with hepatic or renal dysfunction, which could interfere with drug metabolism and excretion. (Hepatic dysfunc- tion is not as much of a problem with nizatidine.) Care should also be taken if prolonged or continual use of these drugs is necessary because they may be masking serious underlying conditions. Adverse effects The adverse effects most commonly associated with H 2 antagonists include the following: GI effects of