McKenna's Pharmacology for Nursing, 2e

533

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

risk of uterine contractions that would harm the fetus or breastfeeding because of the potential for adverse effects to the fetus or baby. The drugs should be stopped during acute illnesses that might lead to fluid and/or electrolyte imbalance, and caution should be used in individuals who consume large amounts of fluid because of the increased risk of electrolyte dilution and hyponatraemia. Adverse effects The adverse effects associated with the use of these drugs include water intoxication (drowsiness, light- headedness, headache, coma, convulsions) related to the shift to water retention and resulting electrolyte imbal­ ance; tremor, sweating, vertigo and headache related to water retention (a “hangover” effect); abdominal cramps, flatulence, nausea and vomiting related to stimu­ lation of GI motility; and local nasal irritation related to nasal administration. Local reaction at injection sites is fairly common. Hypersensitivity reactions have also been reported, ranging from rash to bronchial constriction. Clinically important drug–drug interactions There is an increased risk of antidiuretic effects if the drugs are combined with carbamazepine; use caution if combinations are used.

■■ Posterior pituitary hormones are produced in the hypothalamus and stored in the posterior pituitary. They include oxytocin and antidiuretic hormone (ADH). ■■ Lack of antidiuretic hormone produces diabetes insipidus, which is characterised by large amounts of dilute urine and excessive thirst. ■■ ADH replacement uses an analogue of ADH, desmopressin, and can be administered parenterally or intranasally. ■■ Fluid balance needs to be monitored when individuals are taking desmopressin. ■ ■ Monitor fluid volume to watch for signs of water intoxication and fluid excess ; arrange to decrease dose as needed. ■ ■ Monitor individuals with vascular disease for any sign of exacerbation to provide for immediate treatment. ■ ■ Monitor condition of nasal passages if given intranasally to observe for nasal ulceration, which can occur and could affect absorption of the drug. ■ ■ Provide thorough teaching, including measures to avoid adverse effects, warning signs of problems, and the need for regular evaluation, including blood tests, to enhance knowledge about drug therapy and promote compliance. Evaluation ■ ■ Monitor response to the drug (maintenance of fluid balance). ■ ■ Monitor for adverse effects (GI problems, water intoxication, headache, skin rash). ■ ■ Evaluate the effectiveness of the teaching plan (person can name drug, dosage, adverse effects to watch for and specific measures to avoid them; person can demonstrate proper administration of nasal preparations). ■ ■ Monitor the effectiveness of comfort measures and compliance with the regimen. hypersensitivity reactions ; vascular diseases; epilepsy; renal dysfunction; pregnancy; and breastfeeding, which could be cautions or contraindications to use of the drug. ■ ■ Assess for skin lesions; orientation, affect and reflexes; blood pressure and pulse; respiration and adventitious sounds; abdominal examination; renal function tests; and serum electrolytes, to determine baseline status before beginning therapy and for any potential adverse effects . Implementation with rationale

Prototype summary: Desmopressin Indications: Treatment of neurogenic diabetes insipidus, haemophilia A. Actions: Has pressor and antidiuretic effects; increases levels of clotting factor VIII.

Pharmacokinetics: Route Onset

Peak

Duration

Oral

1 hour

60–90 mins 7 hours 90–120 mins Varies

IV, SC 30 mins

Nasal

15–60 mins 1–5 hours

5–21 hours

T 1/2 : 7.8 minutes, then 75.5 minutes (IV); 1.5 to 2.5 hours (oral); 3.3 to 3.5 hours (nasal); metabolised in the tissues, excretion is unknown. Adverse effects: Headache, facial flushing, nausea, fluid retention, slight increase in blood pressure, local reaction at injection site, water intoxication at high doses. Care considerations for people receiving drugs affecting posterior pituitary hormones Assessment: History and examination ■ ■ Assess for history of allergy to any ADH preparation or components to avoid

KEY POINTS