McKenna's Pharmacology for Nursing, 2e

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

TABLE 59.1

DRUGS IN FOCUS Antiemetic agents (continued)

Drug name

Dosage/route

Usual indications

5-HT 3

receptor blockers (continued)

granisetron (Kytril)

Adult and paediatric (>2 years): 10 mcg/kg IV over 5 mins starting within 30 minutes of chemotherapy; or 1 mg PO b.d. beginning up to 1 hour before chemotherapy and giving the second dose 12 hours after, use only on days of chemotherapy Adult: 8 mg b.d. before chemotherapy, then 8 mg b.d. Paediatric (4–12 years): 4 mg PO t.d.s.; use same IV dose as adults 0.25 mg IV as a single dose over 30 seconds given 30 minutes before the start of chemotherapy; do not repeat dose for 7 days

Treatment of nausea and vomiting associated with emetogenic chemotherapy

Treatment of severe nausea and vomiting associated with emetogenic chemotherapy, radiation therapy, postoperative situations Treatment of acute and delayed vomiting associated with highly emetogenic chemotherapy Treatment of severe nausea and vomiting associated with emetogenic chemotherapy, radiation therapy, postoperative situations

ondansetron (Zilfojim, Zofran)

palonosetron (Aloxi)

tropisetron (Navoban)

Adult: 5 mg/day for 6 days

Substance P/neurokinin 1 receptor antagonists aprepitant (Emend)

125 mg PO 1 hour before chemotherapy (day 1); then 80 mg PO in the morning, on days 2 and 3, with dexamethasone 12 mg PO on day 1 and 8 mg PO on days 2–4, and 32 mg ondansetron IV on day 1 only

Prevention of acute and delayed nausea and vomiting associated with highly emetogenic cancer chemotherapy

fosaprepitant (Emend IV )

Adult 115 mg IV 30 minutes before chemotherapy

Prevention of acute and delayed nausea and vomiting associated with highly emetogenic cancer chemotherapy

P henothiazines The two phenothiazines most commonly used as antiemetics are prochlorperazine ( Stemetil ) and pro- methazine ( Phenergan ), both of which have rapid onset and limited adverse effects. Other drugs in this group include chlorpromazine ( Largactil ). Chapter 22 dis- cusses the phenothiazines in greater detail. ( See the Critical thinking scenario for additional information about caring for a person taking prochlorperazine .) Therapeutic actions and indications Phenothiazines are centrally acting antiemetics that change the responsiveness or stimulation of the CTZ in the medulla (Figure 59.1). The phenothiazines are rec- ommended for the treatment of nausea and vomiting, including that specifically associated with anaesthesia; severe vomiting; and intractable hiccoughs , which occur with repetitive stimulation of the diaphragm and lead to persistent diaphragm spasm. See Table 59.1 for usual indications for each of these agents. Pharmacokinetics These drugs are available as tablets or as syrup for oral administration, as rectal suppositories and as solution

for intramuscular (IM) or intravenous (IV) use. Route of choice is determined by the condition of the person. They have a rapid onset of action of 5 to 20 minutes and duration of action of 3 to 12 hours, depending on route of administration. They are metabolised in the liver and excreted in the urine. They are known to cross the placenta and enter breast milk. Contraindications and cautions In general, antiemetics should not be used in people with coma or severe central nervous system (CNS) depres- sion or in those who have experienced brain damage or injury because of the risk of further CNS depression. Other contraindications include severe hypotension or hypertension and severe liver dysfunction, which might interfere with the metabolism of the drug. Caution should be used in individuals with renal dysfunction, moderate liver impairment, active peptic ulcer or during pregnancy and breastfeeding because of the potential for adverse effects on the fetus or baby . See Chapter 22 for details about the phenothiazines. Adverse effects Adverse effects associated with antiemetics are linked to their interference with normal CNS stimulation or