Chapter 10: Antihypertensive Drugs

Antihypertensive Drugs pharmacology chapter provides an in-depth analysis of antihypertensive drugs and the physiological mechanisms governing blood pressure regulation, specifically the interplay between cardiac output and peripheral vascular resistance mediated by the sympathetic nervous system and the kidneys. The text categorizes hypertension into primary and secondary types and outlines the severe risks of untreated high blood pressure, such as left ventricular hypertrophy, stroke, and renal failure. A significant portion of the chapter focuses on the four major drug classes used for management: diuretics, sympatholytics, angiotensin inhibitors, and vasodilators. It explains how thiazide diuretics, such as hydrochlorothiazide, function by increasing sodium excretion and lowering vascular resistance over time, while potassium-sparing diuretics are often used adjunctively to prevent hypokalemia. The summary details the mechanism of sympatholytic drugs, including alpha-blockers that reduce vascular tone and beta-blockers like metoprolol and carvedilol, which decrease heart rate and renin secretion but are specifically favored for patients with coexisting heart failure or coronary disease. Extensive coverage is given to the renin-angiotensin-aldosterone system (RAAS), describing how ACE inhibitors (e.g., lisinopril) and Angiotensin Receptor Blockers (ARBs like losartan) protect renal function in diabetics and reduce mortality in heart failure, distinguishing them by their side effect profiles such as the bradykinin-mediated cough associated with ACE inhibitors. The text also explores Calcium Channel Blockers (CCBs) like amlodipine and diltiazem, which induce vasodilation by inhibiting calcium influx in smooth muscle. Furthermore, the chapter reviews clinical guidelines for selecting therapy based on patient demographics—such as the preference for diuretics or CCBs in patients of African heritage—and lifestyle modifications like the DASH diet. Finally, it addresses the management of hypertensive emergencies using parenteral vasodilators like nitroprusside and fenoldopam to safely reduce dangerous blood pressure levels without precipitating ischemic damage.