Antihypertensive Drugs

Antihypertensive Drugs Antihypertensive Drugs What is Hypertension? A common, incurable, persistent, but usually asymptomatic disease whose treatment provides no obvious benefit. Why do we treat hypertension? Introduction 30% patients don’t know they have it. 11% are not on therapy. 25% are on inadequate therapy. 34% are on adequate therapy. 3 Average 14 readings: two per session, taken morning 4 and evening for 7 days. BP variations Increased BP variability is associated with increased organ damage and cardiovascular morbidity. “White Coat” or isolated office hypertension. Masked hypertension. Morning surge of BP. During Sleep: “Non dipping’ and “extreme dipping”. 5 - 6 - 7 17 8 Benefits of Lowering BP Antihypertensive therapy has been associated with: 35% to 40% mean reduction in stroke incidence. 20% to 25% reduction in myocardial infarction. More than 50% reduction in HF. 9 - 10 Non-pharmacologic Treatment Lifestyle Modifications: Ø Weight reduction Ø Diet rich in potassium and calcium and sodium reduction. Ø Dietary Approaches to Stop Hypertension (DASH) eating plan( 1600-mg sodium) has effects similar to single drug therapy. Ø Physical activity. 11 Goals of Therapy Maximal protection against cardiovascular consequences with minimal bother to the patient. Stroke, coronary, and renal complications increase when BP is vigorously lowered (Why?) 12 Determinants of Blood Pressure 13 Sites of action of antihypertensive drugs. -17 14 Sites of action of antihypertensive drugs. - 15 - 16 Hemodynamic Effects of Antihypertensive Drugs - 17 - 18 Diuretics (Saluretics) Widely recommended as first-line therapy, especially in the elderly, the obese, and black patients. Better at reducing coronary heart disease, HF, stroke, and mortality. Inexpensive. Combine well with others. Lower doses, with sodium restriction, cause fewer metabolic side effects, but retain antihypertensive activity. All have same efficacy in lowering BP, although not same diuretic activity. 19 Diuretics (Saluretics) Early Effects (3-4 days): – Diuresis lowers blood volume and cardiac output. – Mainly affects the systolic BP. Late Effects (3-4 weeks): – Decreased Na+ & Cl-, lowers blood vessel contractility. Appear even with low doses. Increase Plasma Renin Side Effects: metabolic side effects, ++++ 20 Diuretics (Saluretics) Thiazide diuretics: Effective in mild and moderate Ht with normal renal and heart function. – Hydrochlorthiazide. – Chlorthalidone: long acting. – Bendrofluazide. – Indapamide: vasodilating and lipid neutral. Also induces regression of LVH 21 Diuretics (Saluretics) Loop Diuretics: Needed in severe Ht, in renal insufficiency, and in heart failure or cirrhosis. – Furosemide: not ideal , short acting. – Torsemide: free of metabolic side effects. Potassium- sparing diuretics: Useful in heart failure. – Spironolactone: – Eplerenone. – Ameloride. – Triamterene 22 VASODILATORS Work directly on arterial blood vessels, or veins. Actions not antagonized by known blockers. Reduce peripheral resistance, which will elicit compensatory mechanisms leading to tolerance, resistance or pseudoresistance. Usually other drugs are combined with vasodilators to avoid this problem. 23 Compensatory responses to vasodilators 17 24 - 25 VASODILATORS Hydralazine: Oldest vasodilator(1950s), was withdrawn and then came back. Arteriolar dilator, works by release of NO. Tachyphylaxis (Tolerance or Peusdoresistance). Activates baroreceptor reflex. Metabolized by acetylation. Drug-induced lupus syndrome. Other side effects. Replaced by CCBs.Used in heart failure, combined with isosorbidedi Novn -17itrate 26 VASODILATORS Diazoxide: Thiazide derivative, but not a diuretic. Potent arterial dilator, works by opening potassium channels. Causes excessive hypotension. Used in emergencies by rapid I.V. bolus injection. Rapidly bound to albumin. Onset 10-30 seconds. Duration 2-4 hours. Does not require constant monitoring. 27 VASODILATORS Sodium Nitroprusside: Cyanide-containing molecule. Useful in emergencies, surgery and heart failure. Relaxes both arterial and venous smooth muscle, works by release of NO. No excessive reflex increase in cardiac output. Might increase C.O. if there is failure. 28 VASODILATORS Sodium Nitroprusside: Short half life. Action is immediate, requires constant monitoring in ICU. Drug is light sensitive. Thiocyanate levels and acid-base balance: weakness, nausea, tinnitus, flushing, lactic acidosis and anoxia. 29 - 30 VASODILATORS Minoxidil: K+ channel-opener: increases efflux leading to hyperpolarization. Prolonged arterial relaxation. Superior to hydralazine. For severe intractable hypertension, or renal insufficiency, usually in combination with a diuretic and β blocker. Hypertrichosis, so useful for baldness. Pericarditis. 31 VASODILATORS Fenoldopam: Dopamine D agonist, which results in vasodilation, renal vessel dilation, and natriuresis. Rapidly metabolized, short acting. Used by continuous infusion in emergencies or postoperatively. 1 32 Calcium Channel Blockers More effective than others in protection against stroke. Primarily act to reduce PVR, aided by at least an initial diuretic effect, especially with the short-acting DHPs. Effective in the elderly. Equally effective in blacks and nonblacks. Cause no metabolic disturbances 33 - 34 Calcium Channel Blockers Nifedipine PVR --- HR +++ (Reflexly) CO ++ Diltiazem -- - - Verapamil -- -- -- 35 Angiotensin - Converting Enzyme Inhibitors (ACEI) Angiotensin II: Potent vasoconstrictor by itself. Facilitates release of NE. Central actions to increase BP. Promotes release of aldosterone. Regulates tubular function. Regulates intra-renal blood flow. 36 Angiotensin - Converting Enzyme Inhibitors (ACEI) Inhibit ACE in the lungs. Also inhibit kinin metabolism. 37 Sites of action of drugs that interfere with the renin-angiotensin-aldosterone system. -17 38 Angiotensin - Converting Enzyme Inhibitors (ACEI) Captopril --------------Prototype. Enalapril Quinapril Lisinopril. Benazepril Fosonopril All are similarly effective Might differ in Nov-17 39 Angiotensin - Converting Enzyme Inhibitors (ACEI) Therapeutic Benefits: Effective in high-rennin hypertension (20%), HF and Ischemic Heart Disease. Do not increase HR. Useful in diabetic nephropathy by dilating efferent arterioles thus reducing intraglomerular pressure and consequently protects against progressive glomerulosclerosis. No need for a diuretic but a diuretic can be added. Can be combined with CCBs. Should not be combined with Beta blockers. No metabolic effects.* Contraindicated in pregnancy and bilateral renal artery stenosis. 40 Angiotensin - Converting Enzyme Inhibitors (ACEI) Side Effects: Captopril is SH containing drug, so very toxic( bone marrow suppression, disguesia, proteinuria, allergic skin rash, fever) Hypotension( First Dose Phenomena) especially with renovascular hypertension. K+ retention, especially in the presence of renal dysfunction or when combined with K+ sparing diuretics or ARBs. Cough(10% of patients).Angioedema. 41 Angiotensin II Receptor Blockers (AT-1) Result in more complete inhibition of angiotensin actions (Chymase ?) with no effects on bradykinins. May be only indicated when ACEI are intolerable. Most expensive, but fastest growing class of antihypertensive drugs. Free of side effects, especially cough. May be better than ACEI in protection against stroke (activation of AT-2 receptor facilitates collateral vessels and neuronal resistance). 42 Angiotensin II Receptor Blockers (AT-1) Losartan. Valsartan. Candesartan. Irbesartan. Telmisartan ( additional peroxisome proliferator- activated receptor-g agonist activity). Eprosartan. 43 Chymase Long-term treatment with ACE inhibitors is often associated with so-called “angiotensin escape,” characterized by the return of plasma angiotensin II concentration to pretreatment levels (although the beneficial effects on blood pressure usually persist). This rebound generation of angiotensin II occurs through the action of the serine proteases such as chymase and cathepsin G. 44 45 Chymase Vascular chymase has been implicated in the ACE-independent mechanism for local angiotensin II formation in human arteries. ACE-independent generation of angiotensin II plays a central role in the regulation of renal hemodynamics during the progression of diabetic nephropathy. 46 Chymase The physiologic importance of chymase is uncertain, because of the presence of natural protease inhibitors in the interstitial fluid which inhibit chymase-induced angiotensin II production. 47 Renin Enzyme Inhibitors Aliskiren: – The first in the group. – Other better studied medications are typically recommended due to concerns of higher side effects and less evidence of benefit. 48 Sympatholytics or Adrenergic Blockers Alpha Adrenergic Antagonists – Non selective Antagonists – a1 -Selective Antagonists. Beta Adrenergic Blockers Adrenergic Neurone Blockers. Ganglionic Blockers 49 Non selective Alpha Adrenergic Antagonist Phentolamine Phenoxybenzamine – Block both a1 and a2 receptors, so cause reflex tachycardia and increased contractility. – Blockade of α 2-presynaptic receptors leads to augmented release of NE leading to tachycardia and increased contractility of the heart. – Used only for pheochromocytoma. 50 a1 -selective Alpha Adrenergic Antagonists Prazosin Terazocin Doxazosin Selective (α 1 > α 2) blockers will lower the BP but will not cause tachycardia. First - Dose Phenomenon. All are free of metabolic effects, but can cause drowsiness, diarrhea, postural hypotension, tachycardia, and tolerance due to fluid retention. Effective in moderate hypertension as well as benign prostatic hypertrophy. 51 Beta Adrenergic Blockers Antihypertensive Mechanisms: 1. Decrease HR, SV, and consequently C.O. 2. Decrease Rennin Release 3. Central Action in the vasomotor center. 4. Inhibit NE release 52 Beta Adrenergic Blockers Preparations: 30 Propranolol: Prototype,1957 Timolol Lipophilic Nadolol Long acting Pindolol ISA Acebutelol ISA Esmolol Short half life Metoprolol β1 selective Atenolol β1 selective. Betaxolol β1 selective. Bisoprolol β1 s 53 Beta Adrenergic Blockers Therapeutic Effectiveness: Effect not immediate. Useful in high - rennin hypertension Combination or monotherapy Hyperkinetic hearts Used in other cardiovascular conditions Ineffective in blacks No postural hypotension 54 Beta Adrenergic Blockers Side Effects: Bronchospasm , especially with the non selective Heart Failure? CNS: fatigue, depression, impotence ..etc Impair lipid and glucose metabolism Mask hypoglycemia !!! Claudication, due to α receptor overactivity. Withdrawal Syndrome 55 Vasodilating Beta Adrenergic Blockers Labetalol: – – b, a1 (20% of b) antagonist & b2 partial agonist. Useful for pheochromocytoma and emergencies. Carvedilol: – b, a1 (10% of b) antagonist. Esmolol: – b1 selective, rapidly metabolized. – Used by continuous IV infusion. Nebivolol – b1 selective and nitric oxide-potentiating vasodilatory effect. 56 Adrenergic Neurone Blockers Guanethidine Bethanedine Debrisoquin Guanadrel Hydrophilic. Uptake 1. Block NE release. Displace NE from vesicles ------- MAO. Cause depletion of NE. 57 Life Cycle of Norepinephrine -17 58 Adrenergic Neurone Blockers Reserpine (Rauwolfia Alkaloids): Lipophilic Binds to the sympathetic vesicles. Prevents DA uptake into vesicles. Amines are metabolized by MAO. Depletes: NE, 5HT, ACTH, DA. Old fashioned, slow onset and offset, very cheap. 59 Ganglionic Blockers Trimethaphan Pentolinium Mecamylamine Block transmission in both symp & parasypathetic systems. Act immediately and are very efficacious. Effect rapidly reversed, so used for short term control of BP, e.g. intraoperatively or emergency. Many side effects. 60 61 Centrally Acting Antihypertensive Drugs Vasomotor Center: a Receptor activation decreases BP b Receptor activation increases BP Nucleus Tractus Solitarius Nucleus Ambiguus Rostral Ventral Medulla 62 Autonomic and hormonal control of cardiovascular function 63 Centrally Acting Antihypertensive Drugs Common Properties: Cross BBB. Reduce preganglionic sympathetic activity. Orthostasis is unusual, due to preservation of peripheral sympathetic activity. CNS side effects. 64 Centrally Acting Antihypertensive Drugs 1. Propranolol 2. Reserpine. 3. a- Methyl Dopa: Old drug, thought to work by forming a pseudo transmitter which works peripherally. Central a agonist. a MD-------- a MDA -------- a MNE. Lowers BP but not CO or renal blood flow. Can cause lactation and positive Coomb’s test. Safe in pregnancy. 65 Centrally Acting Antihypertensive Drugs 4. Clonidine: Imidazoline derivative, tried initially as a nasal decongestant. Central a agonist. I.V: Biphasic Effect: peripheral then central actions. Oral. Transdermal Patch(7 days). 66 Causes of Resistant Hypertension Improper BP measurement. “White Coat Hypertension”. Noncompliance. Psychological stresses, secondary hypertension, sleep disorders Volume overload and pseudotolerance. Excess sodium intake Volume retention from kidney disease. Inadequate diuretic therapy. 67 Causes of Resistant Hypertension Inadequate doses. Inappropriate combinations . NSAID; cyclooxygenase 2 inhibitors. Cocaine, amphetamines, other illicit drugs. Sympathomimetics, e.g. decongestants, anorectics 68 Causes of Resistant Hypertension Oral contraceptives Corticosteroids Cyclosporine Erythropoietin Licorice (including some chewing tobacco). Excess alcohol intake. 69 - 70