McKenna's Pharmacology for Nursing, 2e

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C H A P T E R 4 3 Drugs affecting blood pressure

TABLE 43.3

DRUGS IN FOCUS Antihypotensive agents

Drug name

Dosage/route

Usual indications

Alpha-specific adrenergic agent midodrine (Gutron)

10 mg PO t.d.s.

Treatment of orthostatic hypotension in adults

Sympathetic adrenergic agonists or vasopressors See Chapter 30 See Chapter 30

First-choice drugs for treatment of hypotension or shock

Therapeutic actions and indications Sympathomimetic drugs react with sympathetic adren­ ergic receptors to cause the effects of a sympathetic stress response: increased blood pressure, increased blood volume and increased strength of cardiac muscle contraction. These actions increase blood pressure and may restore balance to the cardiovascular system while the underlying cause of the shock (e.g. volume depletion, blood loss) is treated. Adverse effects The adverse effects related to these drugs are the effects of stimulation of the sympathetic system; decreased GI activity with nausea and constipation; increased respira- tory rate and changes in blood pressure; headache; and changes in peripheral blood flowwith numbness, tingling and even gangrene in extreme cases. These drugs should be used with caution with any disease that limits blood Midodrine ( Gutron ) is an alpha-specific adrenergic agent used to treat orthostatic hypotension—hypoten- sion that occurs with position change—that interferes with a person’s ability to function and has not responded to any other therapy (Table 43.3). It is currently availa- ble in New Zealand but not Australia. Therapeutic actions and indications Midodrine activates alpha-receptors in arteries and veins to produce an increase in vascular tone and an increase in blood pressure. It is indicated for the symptomatic treatment of orthostatic hypotension in individuals whose lives are impaired by the disorder and who have not had a response to any other therapy. Pharmacokinetics Midodrine is rapidly absorbed from the GI tract, reaching peak levels within 1 to 2 hours. It is metabo- lised in the liver and excreted in the urine with a half-life of 3 to 4 hours. It should be reserved in pregnancy for cases in which the benefit to the mother clearly flow, with tachycardia or with hypertension. A lpha - specific adrenergic agents

outweighs the potential risk to the fetus. It is not known whether midodrine enters breast milk, so caution should be used during breastfeeding. Contraindications and cautions Midodrine is contraindicated in the presence of supine hypertension, CAD or phaeochromocytoma because of the risk of precipitating a hypertensive emergency ; with acute renal disease, which might interfere with excretion of the drug ; with urinary retention because the stimu- lation of alpha-receptors can exacerbate this problem ; and with thyrotoxicosis, which could further increase blood pressure. Caution should be used with pregnancy and breastfeeding because of the potential for adverse effects on the fetus or neonate ; with visual problems, which could be exacerbated by vasoconstriction ; and with renal or hepatic impairment, which could alter the metabolism and excretion of the drug. Adverse effects The most common adverse effects associated with this drug are related to the stimulation of alpha-receptors and include piloerection, chills and rash; hypertension and bradycardia; dizziness, vision changes, vertigo and headache; and problems with urination. Clinically important drug–drug interactions There is a risk of increased effects and toxicity of cardiac glycosides, beta-blockers, alpha-adrenergic agents and corticosteroids if they are taken with midodrine. People who are receiving any of these combinations should be monitored carefully for the need for a dose adjustment.

Care considerations for people receiving alpha-specific adrenergic agents

Assessment: History and examination

■ ■ Assess for the following conditions, which could be contraindications or cautions : any known allergy to midodrine to prevent hypersensitivity reactions ; impaired kidney or liver function, which could interfere with metabolism and excretion of the