McKenna's Pharmacology for Nursing, 2e

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P A R T 8  Drugs acting on the cardiovascular system

vasodilation causes blood to pool in veins and capil- laries, decreasing preload, while the relaxation of the vessels decreases afterload. The combination of these effects greatly reduces the cardiac workload and the demand for oxygen, thus bringing the supply-and- demand ratio back into balance. Nitrates are indicated for the prevention and treatment of attacks of angina pectoris. See Table 46.1 for usual indications for each of these drugs. Pharmacokinetics Glyceryl trinitrate is available as a sublingual tablet, a translingual spray, an intravenous solution (for bolus injection or infusion), a transdermal patch or a transmu- cosal agent. It can be carried with the person, who then can use it when the need arises. Slow-release forms also are available for use in preventing anginal attacks. Isosorbide dinitrate and isosorbide mononitrate are available in oral form. Nitrates are very rapidly absorbed, metabolised in the liver and excreted in urine. They cross the placenta and enter breast milk. Glyceryl trinitrate is available in many forms; absorption, onset of action and duration vary with the form used (see Prototype summary). Iso- sorbide dinitrate and isosorbide mononitrate, when given orally, have an onset of action in 14 to 45 minutes, or up to 4 hours if the sustained-release (SR) form is used. The drug may have a duration of action of 4 to 6 hours, or 6 to 8 hours if the SR form is used. Contraindications and cautions Nitrates are contraindicated in the presence of any allergy to nitrates. These drugs are also contraindicated in the following conditions: severe anaemia because the decrease in cardiac output could be detrimental in a person who already has a decreased ability to deliver oxygen because of a low red blood cell count ; head trauma or cerebral haemorrhage because the relaxation of cerebral vessels could cause intracranial bleeding ; and pregnancy or breastfeeding because of potential adverse effects on the neonate and ineffective blood flow to the fetus. Caution should be used in people with hepatic or renal disease, which could alter the metabolism and excretion of these drugs. Caution is also required for people with hypotension, hypovolaemia and conditions that limit cardiac output (e.g. tamponade, low ventricu- lar filling pressure, low pulmonary capillary wedge pressure) because these conditions could be exacer- bated, resulting in serious adverse effects. Adverse effects The adverse effects associated with these drugs are related to vasodilation and the decrease in blood flow

Safe medication administration

that occurs. Central nervous system (CNS) effects include headache, dizziness and weakness. Gastrointes- tinal (GI) symptoms can include nausea, vomiting and incontinence. Cardiovascular problems include: hypo- tension, which can be severe and must be monitored; reflex tachycardia that occurs when blood pressure falls; syncope; and angina, which could be exacerbated by the hypotension and changes in cardiac output. Skin- related effects include flushing, pallor and increased perspiration. With the transdermal preparation, there Sublingual, transbuccal and transdermal administration of glyceryl trinitrate Sublingual administration: Individuals often prefer this route of administration, opting to administer the drug themselves even in the institutional setting. Make sure that the drug is given correctly: • Check under the tongue to make sure there are no lesions or abrasions that could interfere with the absorption of the drug. Have the person take a sip of water to moisten the mucous membranes so the tablet will dissolve quickly. Then instruct the person to place the tablet under the tongue, close the mouth and wait until it has dissolved. • Caution the person not to swallow the tablet; its effectiveness would be lost if the tablet entered the stomach. If the person uses sublingual and transbuccal drugs often, encourage them to alternate sides of the tongue—placing it under the left side for one dose, and under the right side for the other dose. • Here’s a tip to help in administering sublingual medications to people who cannot do it themselves or who cannot open their mouths: use a tongue depressor to move the tongue aside and place the tablet, or slide the tablet down through a straw to the underside of the tongue. Transbuccal administration: Make sure that the tablet the person is going to use is designed for buccal administration: • Check the inside of the cheeks to be sure there are no ulcerations or abrasions that could interfere with the absorption of the drug. Have the person place the tablet between their gums and cheek pocket and then hold it in place until the tablet dissolves. • Again, caution the person not to swallow the tablet. Swallowing the tablet will cause systemic absorption. Instruct the person to rotate the site of placement from side to side with each dose. Transdermal administration: Errors have been reported with inappropriate use of glyceryl trinitrate patches and glyceryl trinitrate paste. Make sure to discuss safe administration with the person: • It is very important, even if it seems like common sense, to teach people to remove the old transdermal system and to wash the area before placing a new system to prevent adverse effects such as severe hypotension.