McKenna's Pharmacology for Nursing, 2e

717

C H A P T E R 4 6 Antianginal agents

N itrates Nitrates are drugs that act directly on smooth muscle to cause relaxation and to depress muscle tone. Because the action is direct, these drugs do not influence any nerve or other activity and the response is usually quite fast. Nitrates include isosorbide dinitrate ( Isordil , Sorbidin ), isosorbide mononitrate ( Duride , Imdur and others) and glyceryl trinitrate ( Anginine , Nitro-Dur , Nitrolingual and others). Therapeutic actions and indications The nitrates relax and dilate veins, arteries and capillar- ies, allowing increased blood flow through the vessels and lowering systemic blood pressure because of a drop in resistance. Because CAD causes a stiffening and lack of responsiveness in the coronary arteries, the nitrates probably have very little effect on increasing blood flow through these arteries. However, they do increase blood flow through healthy coronary arteries. Therefore, the blood supply through any healthy vessels in the heart increases, possibly helping the heart to compensate somewhat. The main effect of nitrates, however, seems to be related to the drop in blood pressure that occurs. The PREGNANCY AND BREASTFEEDING The safety for the use of these drugs during pregnancy has not been established.There is a significant potential for adverse effects on the fetus related to blood flow changes and direct drug effects when the drugs cross the placenta.The drugs do enter breast milk, and it is advised that another method of feeding the baby be used if one of these drugs is prescribed during breastfeeding. OLDER ADULTS Older adults frequently are prescribed one of these drugs. Older adults are more likely to develop adverse effects associated with the use of these drugs— arrhythmias, hypotension and heart disease. Safety measures may be needed if these effects occur and interfere with the person’s mobility and balance. Older adults are also more likely to have renal and/or hepatic impairment related to underlying medical conditions, which could interfere with the metabolism and excretion of these drugs.The dose for older adults should be started at a lower level than that recommended for younger adults.The person should be monitored very closely and dose adjusted based on response. If other drugs are added to or removed from the drug regimen, appropriate dose adjustments may need to be made. If the person is using a different form of glyceryl trinitrate, special care should be taken to make sure that the proper administration, storage and timing of use are understood.

and calcium channel blockers are used to treat angina (Figure 46.2). All antianginal agents are effective and may be used in combination to achieve good pain control. The type of drug that is best for a person is determined by toler- ance of adverse effects and response to the drug. The use of antianginal agents with different age groups is dis- cussed in Box 46.1.

↑ Myocardial oxygen consumption

Beta-blockers, calcium channel blockers Beta-blockers, nitrates, calcium channel blockers Beta-blockers, nitrates, calcium channel blockers

↑ Heart rate

↑ Blood volume (preload)

↑ Blood pressure (afterload)

↑ Left ventricular muscle size

Beta-blockers, calcium channel blockers

↑ Muscle contractility

FIGURE 46.2  Interaction of antianginal agents with factors affecting myocardial oxygen demand.

Drug therapy across the lifespan

BOX 46.1

Antianginal agents CHILDREN

The antianginals are not indicated for any condition commonly found in children. In some situations, particularly congenital heart defects or cardiac surgery, glyceryl trinitrate may be used.The dose of the drug should be determined by considering age and weight. The child should be very carefully monitored for adverse reactions, including potentially dangerous changes in blood pressure. ADULTS Adults who receive these drugs should be instructed in their proper administration, particularly if varying forms of glyceryl trinitrate are used. Individuals should also be encouraged to determine what activities or situations tend to precipitate an anginal attack so that they can take measures to avoid those circumstances or take an antianginal agent before the event occurs. With glyceryl trinitrate use, it is important that the person knows how to use the drug, how to store the drug, how to determine whether it is still effective and how much to take before seeking emergency medical care. People should know that regular medical follow- up is important and should be instructed in non- pharmacological measures—weight loss, smoking cessation, activity changes, diet changes—that could decrease their risk of coronary artery disease and improve the effectiveness of the antianginal therapy.