McKenna's Pharmacology for Nursing, 2e

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P A R T 8  Drugs acting on the cardiovascular system

• When the heart muscle is damaged and unable to pump effectively. • With severe blood loss, when volume drops dramatically. • When there is extreme stress and the body’s levels of noradrenaline are depleted, leaving the body unable to respond to stimuli to raise blood pressure. ■■ The cardiovascular system depends on pressure changes to circulate blood to the tissues and back to the heart. ■■ Heart rate, stroke volume and peripheral vascular resistance are factors that determine blood pressure. ■■ Constriction and relaxation of the arterioles result in peripheral resistance. ■■ The baroreceptors stimulate the medulla, which stimulates the sympathetic nervous system to constrict the blood vessels and increase fluid retention if pressure is low in the aorta and the carotid arteries. If pressure is too high, vasodilation and loss of fluid result. ■■ A decrease in blood flow to the kidneys triggers the renin–angiotensin–aldosterone system, by which the blood vessels constrict and water is retained. This activity increases blood pressure and restores blood flow to the kidney. ■■ Hypertension is a sustained state of higher-than- normal blood pressure that can lead to blood vessel damage, atherosclerosis and damage to small vessels in end organs. ■■ The cause of essential hypertension is unknown; treatment varies among individuals. ANTIHYPERTENSIVE AGENTS Because an underlying cause of hypertension is usually unknown, altering the body’s regulatory mechanisms is the best treatment currently available. Drugs used to treat hypertension work to alter the normal reflexes that control blood pressure. See Figure 43.3 for a review of the sites of action of drugs used to treat hypertension. Treatment for essential hypertension does not cure the disease but is aimed at maintaining the blood pressure within normal limits to prevent the damage that hyper- tension can cause. Not all people respond in the same way to antihypertensive drugs because different factors may contribute to each person’s hypertension. Individu- als may have complicating conditions, such as diabetes or acute myocardial infarction (AMI), that make it unwise to use certain drugs. Several different types of drugs that affect differ- ent areas of blood pressure control may need to be used in combination to maintain a person’s blood pressure KEY POINTS

within normal limits. Trials of drugs and combina- tions of drugs are often needed to develop an individual regimen that is effective without producing adverse effects that are unacceptable to the person (Box 43.2). Research is ongoing into the treatment of more specific hypertensions (e.g. pulmonary hypertension). The devel- opment of drugs that target specific blood vessel sites and chemicals could lead to a new approach to the treat- ment of essential hypertension (Box 43.3). Antihypertensive agents include angiotensin- converting enzyme inhibitors, angiotensin II–receptor blockers, calcium channel blockers, vasodilators and other antihypertensive agents, including diuretic agents, ganglionic receptors, renin inhibitors and sympathetic nervous system drugs. See Table 43.2 for a complete list of antihypertensive agents. See Box 43.4 for use of these agents across the lifespan. Treating hypertension The importance of treating hypertension has been proven in numerous research studies. If hypertension is controlled, the person’s risk of cardiovascular death and disease is reduced. The risk of developing cardiovascular complications is directly related to the person’s degree of hypertension (see Table 43.1). Lowering the degree of hypertension lowers the risk. Hypertensive treatment is further complicated by the presence of other chronic conditions. The Heart Foun- dation has published an algorithm for the treatment of hypertension to help prescribers select an antihyper- tensive agent in the light of complicating conditions (Figure 43.4). A person’s response to a given antihyper- tensive agent is very individual, so the drug of choice for one person may have little to no effect on another person. A ngiotensin - converting - enzyme inhibitors The angiotensin-converting-enzyme (ACE) inhibi- tors include the following agents: captopril ( Capoten , Zedace , others), enalapril ( Acetec , Amprace , Renitec , others), fosinopril ( Monace , Monopril ), lisinopril ( Fibsol , Prinivil , Zestril , others), perindopril ( Coversyl , Indopril, Perindo ), quinapril ( Accupril , Acquin, Qpril ), ramipril ( Prilace , Ramace ) and trandolapril ( Dolapril, Gopten ). Therapeutic actions and indications ACE inhibitors act in the lungs to prevent ACE from converting angiotensin I to angiotensin II, a powerful vasoconstrictor and stimulator of aldosterone release (see Figure 43.3). This action leads to a decrease in blood pressure and in aldosterone secretion, with a resultant slight increase in serum potassium and a loss of serum sodium and fluid.