Chapter 43: Drugs Affecting Blood Pressure

Drugs Affecting Blood Pressure provides a foundational exploration of the drugs utilized to regulate blood pressure (BP), addressing both hypertension and hypotension, offering essential information for nursing pharmacology. The cardiovascular (CV) system maintains pressure based on heart rate, stroke volume (which relates to blood volume), and total peripheral resistance, mainly controlled by the constriction and relaxation of arterioles. The body regulates BP continually through two main systems: the fast-acting baroreceptor reflex (pressure receptors in the aorta and carotid artery influencing the cardiovascular center in the medulla) and the hormonal Renin–Angiotensin–Aldosterone System (RAAS). In the RAAS, decreased kidney perfusion triggers renin release, leading to the formation of angiotensin II, a potent vasoconstrictor that also stimulates aldosterone release, ultimately increasing BP and fluid retention. The majority of patients suffer from essential hypertension, meaning high BP with no discernible underlying cause, and treatment begins with intensive lifestyle modifications. Pharmacological intervention for hypertension aims to interrupt these regulatory mechanisms. Major drug classes include Angiotensin-Converting Enzyme (ACE) inhibitors (e.g., captopril), which block the conversion of angiotensin I to angiotensin II in the lungs and are known to cause a persistent cough; Angiotensin II Receptor Blockers (ARBs) (e.g., losartan), which selectively bind to angiotensin II receptors, blocking its effects; and the renin inhibitor (aliskiren), which blocks the system at the start. Both ACE inhibitors and ARBs are strictly contraindicated during pregnancy due to the risk of serious fetal harm. Calcium-channel blockers (CCBs) (e.g., diltiazem) lower BP by inhibiting calcium influx into myocardial and arterial muscle cells, which decreases cardiac contractility and causes vasodilation. For severe hypertensive emergencies, potent vasodilators (like nitroprusside) are utilized, though nitroprusside carries a risk of cyanide toxicity. Other agents include diuretics and various sympathetic nervous system blockers (e.g., beta-blockers). It is important to note ethnic variations in response, such as African American patients often responding better to diuretics or CCBs than to RAAS inhibitors. Conversely, hypotension may progress to life-threatening shock if perfusion is severely impaired. Acute shock is managed using sympathomimetic drugs (vasopressors). For chronic symptomatic orthostatic hypotension, oral agents like midodrine and droxidopa (a precursor metabolized to norepinephrine) are used to raise BP in mobile patients.