McKenna's Pharmacology for Nursing, 2e

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

in New Zealand]), telmisartan ( Micardis [not available in New Zealand]) and valsartan ( Diovan [not available in New Zealand]). Therapeutic actions and indications The ARBs selectively bind with the angiotensin II recep- tors in vascular smooth muscle and in the adrenal cortex to block vasoconstriction and the release of aldosterone. These actions block the blood pressure–raising effects of the renin–angiotensin system and lower blood pressure. They are indicated to be used alone or in combination therapy for the treatment of hypertension and for the treatment of heart failure in individuals who are intol- erant to ACE inhibitors. Recently, they were also found to slow the progression of renal disease in people with hypertension and type 2 diabetes. This action is thought to be related to the effects of blocking angiotensin recep- tors in the vascular endothelium. See Table 43.2 for indications for each drug. Pharmacokinetics These agents are all given orally. They are well absorbed and undergo metabolism in the liver by the cytochrome P450 system. They are excreted in faeces and in urine. The ARBs cross the placenta. It is not known whether they enter breast milk during breastfeeding (see Contra­ indications and cautions). Contraindications and cautions The ARBs are contraindicated in the presence of allergy to any of these drugs to prevent hypersensitivity reac- tions . Caution should be used in the presence of hepatic or renal dysfunction, which could alter the metabolism and excretion of these drugs , and with hypovolae- mia, because of the blocking of potentially life-saving compensatory mechanisms. These drugs are also con- traindicated during pregnancy: candesartan, eprosartan, irbesartan, olmesartan and telmisartan should not be used during the second or third trimester of pregnancy because of association with serious fetal abnormalities and even death when given in the second or third tri- mester ; losartan and valsartan should not be used at any time during pregnancy. Although it is not known whether the ARBs enter breast milk during breastfeed- ing, these drugs should not be used during breastfeeding because of the potential for serious adverse effects in the neonate. Women of childbearing age should be advised to use barrier contraceptives to avoid pregnancy; if a pregnancy does occur, the ARB should be discontinued immediately. Adverse effects The adverse effects most commonly associated with ARBs include the following: headache, dizziness,

A ngiotensin II– receptor blockers The angiotensin II–receptor blockers (ARBs) include the following drugs: candesartan ( Atacand ), eprosar- tan ( Teveten ), irbesartan ( Abisart, Avapro ), losartan ( Cozaar, Cozavan ), olmesartan ( Olmetec [not available decreased alcohol and salt in the diet, and increased exercise, to increase the effectiveness of antihypertensive therapy. ■ ■ Administer on an empty stomach 1 hour before or 2 hours after meals to ensure proper absorption of the drug. ■ ■ Alert the surgeon and mark the person’s chart prominently if the person is to undergo surgery to alert medical personnel that the blockage of compensatory angiotensin II could result in hypotension after surgery that would need to be reversed with volume expansion. ■ ■ Consult with the prescriber to reduce the dose in individuals with renal failure to account for their decreased production of renin and lower-than- normal levels of angiotensin II. ■ ■ Monitor the person carefully in any situation that might lead to a drop in fluid volume (e.g. excessive sweating, vomiting, diarrhoea, dehydration) to detect and treat excessive hypotension that may occur. ■ ■ Provide comfort measures to help the person tolerate drug effects. These include small, frequent meals; access to bathroom facilities; bowel program as needed; environmental controls; safety precautions; and appropriate skin care as needed. ■ ■ Provide thorough teaching, including the name of the drug, dosage prescribed, measures to avoid adverse effects, warning signs of problems and the need for periodic monitoring and evaluation, to enhance knowledge about drug therapy and to promote compliance. ■ ■ Offer support and encouragement to help the person deal with the diagnosis and the drug regimen. Evaluation ■ ■ Monitor response to the drug (maintenance of blood pressure within normal limits). ■ ■ Monitor for adverse effects (hypotension, cardiac arrhythmias, renal dysfunction, skin reactions, cough, pancytopenia, heart failure). ■ ■ Evaluate the effectiveness of the teaching plan (person can name drug, dosage, adverse effects to watch for, specific measures to avoid them and the importance of continued follow-up). ■ ■ Monitor the effectiveness of comfort measures and compliance with the treatment regimen.