McKenna's Pharmacology for Nursing, 2e

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

response. Drowsiness, dizziness, weakness, tremor and headache are common adverse effects. Other, not uncommon adverse effects include hypotension, hyper- tension and cardiac arrhythmias. Autonomic effects such as dry mouth, nasal congestion, anorexia, pallor, sweating and urinary retention often occur with phe- nothiazines. People should be cautioned that their urine may be tinged pink to red-brown. This is a drug effect but can cause concern if the person is not expecting it. Endocrine effects such as menstrual disorders, galac- torrhoea and gynaecomastia have been reported with phenothiazine use. Photosensitivity (increased sen- sitivity to the sun and ultraviolet light) is a common adverse reaction with these antiemetics. People should be advised to use sunscreens and protective garments if exposure cannot be avoided. Clinically important drug–drug interactions Additive CNS depression can be seen with any of the antiemetics if they are combined with other CNS depressants, including alcohol. People should be advised to avoid this combination and any OTC preparation unless they check with their healthcare provider. Other drug–drug interactions are specific to each drug (refer to a nursing or midwifery drug guide). • Dehydration : Avoid excessive heat exposure, and try to drink fluids as much as possible, because you will have an increased risk of heat stroke. • Report any of the following conditions to your healthcare provider: fever, rash, yellowing of the eyes or skin, dark urine, pale stools, easy bruising, rash and vision changes. Prototype summary: Prochlorperazine Indications: Control of severe nausea and vomiting. Actions: Mechanism of action not understood; depresses various areas of the CNS, including the CTZ in the medulla. Pharmacokinetics: Route Onset Peak Duration Oral 30–40 mins Unknown 3–4 hours Rectal 60–90 mins Unknown 3–4 hours IM 10–20 mins 10–30 mins 3–4 hours IV Immediate 10–30 mins 3–4 hours T 1/2 : Unknown; metabolised in the liver and excreted in urine. Adverse effects: Drowsiness, dystonia, photophobia, blurred vision, urine discoloured pink to red- brown.

• Avoid over-the-counter (OTC) medications. If you feel that you need one, check with your healthcare provider first. • Tell any doctor, nurse or other healthcare provider that you are taking this drug. • Keep this drug and all medications out of the reach of children.

O ther dopamine D 2

receptor antagonists

Two other non-phenothiazine dopamine D 2 receptor antagonists currently available for use as antiemet- ics are metoclopramide ( Maxolon ) and domperidone ( Motilium ). These act to reduce the responsiveness of the nerve cells in the CTZ to circulating chemicals that induce vomiting. Chapter 58 discusses metoclopramide, which is also commonly used to treat gastroparesis, in greater detail. Prototype summary: Metoclopramide Indications: Prevention of nausea and vomiting associated with emetogenic cancer chemotherapy; prevention of postoperative nausea and vomiting. Actions: Slows GI activity; sedating. Pharmacokinetics: Route Onset Peak Duration Oral 30–60 mins 60–90 mins 1–2 hours IM 10–15 mins 60–90 mins 1–2 hours IV 1–3 mins 60–90 mins 1–2 hours T 1/2 : 5–6 hours; metabolised in the liver and excreted in urine. Adverse effects: Drowsiness, fatigue, restlessness, extrapyramidal symptoms, diarrhoea. The 5-HT 3 receptor blockers block those receptors asso- ciated with nausea and vomiting in the CTZ and locally. These drugs include dolasetron ( Anzemet ), granisetron ( Kytril ), ondansetron ( Zofran ), palonosetron ( Aloxi ) and tropisetron ( Navoban ). Therapeutic actions and indications The 5-HT 3 receptor blockers have proven especially helpful in treating the nausea and vomiting associated with antineoplastic chemotherapy, radiation therapy, and postoperative nausea and vomiting. They are specific for the treatment of nausea and vomiting associated 5-HT 3 receptor blockers