McKenna's Pharmacology for Nursing, 2e

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P A R T 6  Drugs acting on the endocrine system

these individuals because of the systemic effects of the drugs.

■ ■ Monitor for adverse effects (hypothyroidism, glucose intolerance, nutritional imbalance, GI disturbances, headache, dizziness, cholecystitis). ■ ■ Evaluate the effectiveness of the teaching plan (person can name drug, dosage, adverse effects to watch for and specific measures to avoid them; family member can demonstrate proper technique for preparation and administration of drug). ■ ■ Monitor the effectiveness of comfort measures and compliance with the regimen.

DRUGS AFFECTING POSTERIOR PITUITARY HORMONES

The posterior pituitary stores two hormones produced in the hypothalamus: antidiuretic hormone (ADH, also known as vasopressin) and oxytocin. Oxytocin stimulates milk ejection or “let down” in breastfeed­ ing women. In pharmacological doses, it can be used to initiate or improve uterine contractions in labour. Oxytocin is discussed in Chapter 40. ADH possesses antidiuretic, haemostatic and vaso­ pressor properties. Posterior pituitary disorders can occur secondary to metastatic cancer, lymphoma, dis­ seminated intravascular coagulation (discussed in Chapter 48) or septicaemia. Posterior pituitary dis­ orders that are seen clinically involve ADH release and include diabetes insipidus , which results from insufficient secretion, and syndrome of inappropri­ ate antidiuretic hormone (SIADH), which occurs with excessive secretion of ADH. Diabetes insipidus can be treated pharmacologically. ( See the Critical thinking scenario related to diabetes insipidus and posterior pituitary hormones. ) Diabetes insipidus is characterised by the production of a large amount of dilute urine containing no glucose. Blood glucose levels are higher than normal, and the body responds with polyuria (excessive urine), poly­ dipsia (excessive thirst) and dehydration. With this rare metabolic disorder, individuals produce large quantities of dilute urine and are constantly thirsty. Diabetes insip­ idus is caused by a deficiency in the amount of posterior pituitary ADH and may result from pituitary disease or injury (e.g. head trauma, surgery, tumour). The condi­ tion can be acute and short in duration or it can be a chronic, lifelong problem. ADH itself is never used as therapy for diabetes insipidus. Instead, synthetic preparations of ADH, which are purer and have fewer adverse effects, are used. The ADH preparations currently available are desmo­ pressin ( Minirin , Octostim ) and vasopressin ( Pitressin ) (see Table 35.3). Therapeutic actions and indications ADH is released in response to increases in plasma osmolarity or decreases in blood volume. It produces its antidiuretic activity in the kidneys, causing the cortical and medullary parts of the collecting duct to become permeable to water, thereby increasing water reabsorp­ tion and decreasing urine formation. These activities reduce plasma osmolarity and increase blood volume. See Table 35.3 for usual indications for desmopressin and vasopressin.

D rugs affecting other anterior pituitary hormones

Drugs that affect growth hormone are the most com­ monly used drugs affecting anterior pituitary hormones. There are several other anterior pituitary hormones that can now be affected by drugs. The other anterior pituitary hormones that are available for pharmaco­ logical use include chorionic gonadotropin ( Pregnyl ), choriogonadotropin alfa ( Ovidrel ) and thyrotropin alfa ( Thyrogen ) (not available in New Zealand). Chorionic gonadotropin acts like LH and stimulates the production of testosterone and progesterone. Usual indications are presented in Table 35.2. (See Chapters 40 and 41 for nursing implications.) Choriogonadotropin alfa is used as a fertility drug to induce ovulation in women treated with FSH (see Chapters 40 and 41). Thyrotropin alfa is used as adjunctive treatment for radioiodine ablation of thyroid tissue remnants in people who have undergone a near-total to total thyroidectomy for well-differentiated thyroid cancer and who do not have evidence of metastatic thyroid cancer. Cabergoline ( Bergoline ) acts on dopamine receptors located on pituitary lactotrophic cells to decrease pro­ lactin secretion. ■■ Hypothalamic releasing factors stimulate the anterior pituitary to release hormones, which in turn stimulate endocrine glands or cell metabolism. The anterior pituitary hormones are mostly used for diagnostic testing, for treating some cancers or in fertility programs. ■■ In children, deficiency of GH may be responsible for dwarfism; in adults it is associated with somatropin deficiency syndrome. ■■ GH may be replaced by substances produced by recombinant DNA processes, which are safer than replacement drugs used in the past. ■■ In cases of GH excess, drugs are used to block the effects of GH. Care must be taken to monitor KEY POINTS