McKenna's Pharmacology for Nursing, 2e

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

Evaluation

Safe medication administration

C alcium channel blockers Calcium channel blockers decrease blood pressure, cardiac workload and myocardial oxygen consump- tion. The effects of these drugs on cardiac workload also make them very effective in the treatment of angina (see Chapter 46). The calcium channel blockers avail- able in immediate-release and sustained-release forms that are used in treating hypertension are amlodipine ( Norvasc ), felodipine ( Fendex ER, Plendil ER ) and isradipine ( DynaCirc SRO [not available in Australia]). Other calcium channel blockers are safe and effective for this use only if they are given as sustained-release or extended release preparations. These include diltiazem ( Cardizem , Dilzem ), lercanidipine ( Lercan , Zanidip , Zircol ), nifedipine ( Adalat , Adefin , Nyefax ) and verapa- mil ( Anpec , Isoptin , Cordilox SR ). See Contraindications and cautions for important safety information regarding use of controlled-release products. Therapeutic actions and indications Calcium channel blockers inhibit the movement of calcium ions across the membranes of myocardial and arterial muscle cells, altering the action potential and blocking muscle cell contraction. This effect depresses myocardial contractility, slows cardiac impulse forma- tion in the conductive tissues and relaxes and dilates arteries, causing a fall in blood pressure and a decrease in venous return. See Table 43.2 for indications for each of these drugs. Pharmacokinetics Calcium channel blockers are given orally and are gener- ally well absorbed, metabolised in the liver and excreted in the urine. These drugs cross the placenta and enter breast milk (see Contraindications and cautions). Contraindications and cautions These drugs are contraindicated in the presence of allergy to any of these drugs to prevent hypersensitivity ■ ■ Monitor response to the drug (maintenance of blood pressure within normal limits). ■ ■ Monitor for adverse effects (hypotension, GI distress, skin reactions, cough, headache, dizziness). ■ ■ Evaluate the effectiveness of the teaching plan (person can name drug, dosage, adverse effects to watch for, measures to avoid them and the importance of continued follow-up). ■ ■ Monitor the effectiveness of comfort measures and compliance with the regimen.

reactions ; with heart block or sick sinus syndrome, which could be exacerbated by the conduction-slowing effects of these drugs ; and with renal or hepatic dysfunc- tion, which could alter the metabolism and excretion of these drugs. Although there are no well-defined studies about effects during pregnancy, fetal toxicity has been reported in animal studies; therefore, these drugs should not be used during pregnancy unless the benefit to the mother clearly outweighs any potential risk to the fetus because of the potential for adverse effects on the fetus or neonate. Because of the potential for serious adverse effects on the baby , another method of feeding the infant should be used if these drugs are required during breastfeeding. Adverse effects The adverse effects associated with these drugs relate to their effects on cardiac output and on smooth muscle. CNS effects include dizziness, light-headedness, headache and fatigue. GI problems include nausea and hepatic injury related to direct toxic effects on hepatic cells. Cardiovascular effects include hypotension, brady- cardia, peripheral oedema and heart block. Skin flushing and rash may also occur. Clinically important drug–drug interactions Drug–drug interactions vary with each of the calcium channel blockers used to treat hypertension. A poten- tially serious effect to note is an increase in serum levels and toxicity of cyclosporin if taken with diltiazem. Clinically important drug–food interactions The calcium channel blockers are a class of drugs that interact with grapefruit juice. When grapefruit juice is present in the body, the concentrations of calcium channel blockers increase, sometimes to toxic levels. Advise people to avoid the use of grapefruit juice if they are taking a calcium channel blocker. If a person Several drugs that are used to treat hypertension cannot be cut, crushed or chewed. This is very important information to share with people on antihypertensive drugs. Sometimes individuals cut tablets in half to facilitate swallowing or to get twice the number of days for any given prescription. Most drugs formulated for extended release or sustained release are delivered in a matrix system that slowly dispenses the drug into the system. If the coating of the matrix is cut, all of the drug is released at once, leading to the release of too much drug at one time and, consequently, toxic levels of the drug when first taking it. Then the person receives no drug as the day goes on. Some antihypertensives to be aware of are diltiazem, nifedipine and verapamil.