McKenna's Pharmacology for Nursing, 2e

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C H A P T E R 3 5 Hypothalamic and pituitary agents

disorder (e.g. diabetes, thyroid dysfunction) that could be exacerbated by the blocking of GH. Adverse effects People with renal dysfunction may accumulate higher levels of octreotide. GI complaints (e.g. constipation or diarrhoea, flatulence and nausea) are not uncommon because of the drug’s effects on the GI tract. Octreo­ tide and lanreotide have also been associated with the development of acute cholecystitis, cholestatic jaundice, biliary tract obstruction and pancreatitis. People must be assessed for the possible development of any of these problems. Other, less common adverse effects include headache, sinus bradycardia or other cardiac arrhythmias and decreased glucose tolerance. Because octreotide and lanreotide are administered subcutane­ ously, they can be associated with discomfort and/or inflammation at injection sites. Bromocriptine is also associated with GI disturb­ ances. Because of its dopamine-blocking effects, it may cause drowsiness and postural hypotension. It blocks breastfeeding and should not be used by breastfeeding women. Pegvisomant may cause pain and inflammation at the injection site (common). Increased incidence of infec­ tion, nausea and diarrhoea and changes in liver function may also occur. Clinically important drug–drug interactions Increased serum bromocriptine levels and increased toxicity occur if bromocriptine is combined with eryth­ romycin. This combination should be avoided. The effectiveness of bromocriptine may decrease if it is combined with phenothiazines. If this combination is used, the person should be monitored carefully. People receiving pegvisomant may require higher doses to receive adequate GH suppression if they are also taking opioids. The mechanism of action of this interaction is not understood. Prototype summary: Bromocriptine mesylate Indications: Treatment of Parkinson’s disease, hyperprolactinaemia associated with pituitary adenomas, female infertility associated with hyperprolactinaemia and acromegaly; short-term treatment of amenorrhoea or galactorrhoea. Actions: Acts directly on postsynaptic dopamine receptors in the brain. Pharmacokinetics: Route Onset Peak Duration PO Varies 1–3 hours 14 hours

T 1/2 : 3 hours, then 45 to 50 hours; metabolised in the liver and excreted in the bile. Adverse effects: Dizziness, fatigue, light-headedness, nasal congestion, drowsiness, nausea, vomiting, abdominal cramps, constipation, diarrhoea, headache.

Care considerations for people receiving growth hormone antagonists

Assessment: History and examination

■ ■ Assess for history of allergy to any GH antagonist or binder to prevent hypersensitivity reactions ; other endocrine disturbances, which could be exacerbated when blocking GH ; and pregnancy and breastfeeding because of the potential for adverse effects to the fetus and the blocking of breastfeeding. ■ ■ Assess orientation, affect and reflexes; blood pressure, pulse and orthostatic blood pressure; abdominal examination; glucose tolerance tests and GH levels, to determine baseline status before beginning therapy and for any potential adverse effects . Implementation with rationale ■ ■ Reconstitute octreotide and pegvisomant following manufacturer’s directions; administer these drugs subcutaneously and rotate injection sites regularly to prevent skin breakdown and to ensure proper delivery of the drug. ■ ■ Monitor thyroid function, glucose tolerance and GH levels periodically to detect problems and to institute treatment as needed. ■ ■ Arrange for baseline and periodic ultrasound evaluation of the gallbladder if using octreotide to detect any gallstone development and to arrange for appropriate treatment. ■ ■ Provide thorough teaching, including measures to avoid adverse effects, warning signs of problems and need for regular evaluation (including blood tests), to enhance knowledge about drug therapy and promote compliance. Instruct a family member in proper preparation and administration techniques to ensure that there is another responsible person to administer the drug if needed. Evaluation ■ ■ Monitor response to the drug (return of GH levels to normal, growth and development).