McKenna's Pharmacology for Nursing, 2e

903

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

Clinically important drug–drug interactions Cimetidine, famotidine and ranitidine can slow the metabolism of the following drugs, leading to increased serum levels and possible toxic reactions: warfarin anticoagulants, phenytoin, beta-adrenergic blockers, alcohol, quinidine, lignocaine, theophylline, chloroquine, benzodiazepines, nifedipine, tricyclic anti- depressants, procainamide and carbamazepine. There is a risk of increased salicylate levels if nizatidine is taken with aspirin. • Report any of the following to your healthcare provider : sore throat, unusual bleeding or bruising, confusion, muscle or joint pain, tarry stools. • Avoid taking any OTC medication without first checking with your healthcare provider. Several of these medications can interfere with the effectiveness of this drug. • If an antacid has been ordered for you, take it exactly as prescribed, spaced apart from your ranitidine. • Tell any doctor, nurse or other healthcare provider involved in your care that you are taking this drug. • If you are taking any other medications, do not vary the drug schedules. Consult with your primary healthcare provider if anything should happen to change any of these drugs or your scheduled doses. • It is important to have regular medical follow-up while you are taking this drug to evaluate your response to the drug and any possible underlying problems. • Keep this drug, and all other medications, out of the reach of children. ■ ■ Assess for possible contraindications or cautions : history of allergy to any H 2 antagonists to prevent potential allergic reactions ; impaired renal or hepatic function, which could affect metabolism and excretion of the drug ; a detailed description of the GI problem, including length of time of the disorder and medical evaluation, to evaluate the appropriate use of the drug and possibility of underlying medical problems ; and current status of pregnancy or breastfeeding because of the potential for adverse effects on the fetus or newborn. ■ ■ Perform a physical examination to establish baseline data before beginning therapy, determine effectiveness of the therapy and evaluate for any adverse effects associated with drug therapy. Care considerations for people receiving histamine-2 antagonists Assessment: History and examination

diarrhoea or constipation; central nervous system (CNS) effects of dizziness, headache, somnolence, confusion or even hallucinations (thought to be related to possible H 2 receptor effects in the CNS); cardiac arrhythmias and hypotension (related to H 2 cardiac receptor blocking; more commonly seen with intravenous or intramuscular administration or with prolonged use); and gynaeco- mastia (more common with long-term use of cimetidine) and impotence. Prototype summary: Cimetidine Indications: Short-term treatment of active duodenal or benign gastric ulcers; treatment of pathological hypersecretory conditions; prophylaxis of stress- induced ulcers; treatment of erosive gastro- oesophageal reflux; relief of symptoms of heartburn and acid indigestion. Actions: Inhibits the actions of histamine at H 2 receptor sites of the stomach, inhibiting gastric acid secretion and reducing total pepsin output. Monitor for drug–drug interactions as listed. Evaluate the effectiveness of the teaching program. Evaluate the effectiveness of comfort and safety measures. TEACHING FOR W.T. • The drug that has been prescribed for you, ranitidine, is called a histamine-2 antagonist. A histamine-2 antagonist decreases the amount of acid that is produced in the stomach. It is used to treat conditions that are aggravated by excess acid. • Some of the following adverse effects may occur with this drug: • Diarrhoea : Have ready access to bathroom facilities. This usually becomes less severe over time. • Dizziness, headache : These usually lessen as your body adjusts to the drug. Change positions slowly. If you feel drowsy, avoid driving or dangerous activities.

Pharmacokinetics: Route Onset

Peak

Duration

Oral

Varies

1–1.5 hours 4–5 hours 1–1.5 hours 4–5 hours

IM, IV Rapid

T 1/2 : 2 hours; metabolised in the liver and excreted in urine. Adverse effects: Dizziness, confusion, headache, somnolence, cardiac arrhythmias, cardiac arrest, diarrhoea, impotence, gynaecomastia, rash.