Week 7 - Hypertension Treatments Flashcards by Annabel Cookson

Why treat hypertension?

major risk factor for stroke

- major risk factor for ischaemic heart disease - e.g. angina, MI

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When is hypertension treated?

-sustained systolic BP of >160mmHg
OR
-sustained diastolic BP of >100mmHg

If known CV disease, diabetes or organ damage:
-sustained systolic 140-159mmHg
OR
-sustained diastolic BP of 90-99mmHg

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What are the types of anti hypertensive drugs?

Diuretics

Vasodilators (calcium antagonists, a1-blockers, angiotensin antagonists)

B-blockers

ACE inhibitors

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How is BP calculated?

BP = CO (cardiac output) X TPR (total peripheral resistance)

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How can cardiac output be reduced?

HR
stroke volume
plasma volume

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How can total peripheral resistance be reduced?

-dilating arterioles

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What do diuretics do?

reduce plasma volume then gradually TPR

- act on the kidney to increase diuresis

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What do vasodilators do?

Directly lower TPR

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What do B-blockers do?

Reduce cardiac output and kidney renin secretion

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What do ACE inhibitors do?

Inhibit endogenous vasoconstrictor production

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What do a-blockers do?

Reduce TPR by inhibiting noradrenaline action

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What do angiotensin antagonists do?

Reduce TPR by inhibiting angiotensin action

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What are the actions of diuretics?

increase Na+ excretion (reduce salt reabsorption from glomerular filtrate)
water loss follows
reduce plasma volume
reduce cardiac output

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What are the types of diuretics?

thiazide diuretics

- loop diuretics

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Describe thiazide diuretics

moderately potent diuretics
reduce systolic and diastolic pressure
widely used antihypertensive, suitable for most patients
inhibit Na+, Cl- co-transport in distal tubule
additional vasodilator action
potentiate effects of other antihypertensives
increase renin release (may counteract effects on BP)

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What is the mechanism of action of thiazide diuretics?

Inhibit Na+, Cl- co-transport in distal tubule

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Name some examples of thiazide diuretics

Derived from benzothiadiazine:

chlorothiazide
hydrochlorothiazide
bendrofluazide

Thiazide like structure:

chlorthalidone
metolazone

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What are the side effects of thiazides?

-more frequent urination
but
-high safety
-low profile of side effects

Describe loop diuretics

very potent diuretics
no more effective than thiazides at reducing BP
reserved for use in patients with renal insufficiency, resistant hypertension or heart failure

Name the different types of vasodilator drugs

Calcium antagonists (main type)

A1-blockers 
Angiotensin antagonists (both used but less often)

Potassium channel activators
Sodium nitroprusside
Hydralazine (others used in special circumstances)

What is the action of vasodilators?

act directly on the smooth muscle cells of arteries and arterioles
lower the intracellular calcium concentration
cause muscle cell relaxation
results in vasodilation

Name some caccium channel antagonists

Dihydropyridines

amlodipine
nicardipine
nifedipine

Benzothiazepine
-diltiazem

-verapamil

What are calcium channel antagonists mechanism of action?

Block Ca2+ entry through voltage-operated calcium channels in arterial smooth muscle cells - vasodilation

Describe how Dihydropyridines act

-highly selective for smooth muscle but affect most smooth muscle

nifedipine
amlodipine - longer acting (once daily dose)
nicardipine - some selectively for cerebral and coronary arteries

Describe how benzothiazepines act

- also block calcium channels in the conducting tissue of the heart - diltiazem - slows heart rate, potentiate a B-blocker action

What are the side effects of calcium antagonists?

All: - flushing - ankle oedema Diltiazem: - cardiac depression - interaction with B-blockers

What is the mechanism of action of a1-blockers?

- drugs used for hypertension are selective blockers of a1-adrenoceptors - prevent vasoconstrictor action of endogenous noradrenaline

Name some examples of alpha receptor antagonists/a1-blockers

- doxazosin - once daily - terazosin - once daily - prazosin - shorter acting, 3X daily

What are the adverse effects of a1-blockers

-postural hypertension (dizziness, light headedness) -possible severe hypotension after first dose but -generally well tolerated

Name some examples of B-blockers

- atenolol | - metoprolol

What is the mechanism of action of B-blockers?

- bind to and block B1-adrenoreceptors in the heart (sino atrial node and ventricular muscle) - block action of noradrenaline released from sympathetic nerves and circulating adrenaline

What is the initial effect of B-blockers?

- reduce rate and force of heart beat | - decrease cardiac output

What is the effect of bB-blockers after continued treatment?

- CO returns to normal but BP remains low | - TPR reset at lower level

What are the adverse effects of B-blockers?

Common: - cold hands - fatigue Less common but serious: - can provoke asthma attack in asthmatic - heart failure - conduction block in heart Also: -may affect blood lipids

Name some examples of ACE inhibitors

Angiotensin-converting enzyme inhibitors - captopril - 2x daily dose - enalapril -single daily dose - lisinopril - lysine analogue of enalapril - ramipril

What system do ACE inhibitors have an effect on?

Renin angiotensin system Angiotensinogen--> (renin helps convert to) angiotensin I --> (angiotensin converting enzyme (ACE helps convert to)) angiotensin II --> vasoconstriction

What is the mechanism of action of ACE inhibitors?

-prevent conversion of angiotensin I to angiotensin II (potent vasoconstrictor, stimulates aldosterone secretion - which inhibits salt and H2O excretion) - causes vasodilation - reduces plasma volume

What are the adverse effects of ACE inhibitors?

- dry cough - hypotension initially, especially if given with a diuretic - these effects usually wear off with time

Name some angiotensin II receptor antagonists

- losartan - candesartan - eprosartan - valsartan

What is the mechanism of action of angiotensin II receptor antagonists?

- block the action of angiotensin II (vasoconstriction) at its receptors - competes for binding to AT receptors - so vasodilation

How and when are angiotensin II receptor antagonists used?

- in combination with an ACE inhibitor (improved mortality and morbidity vs. ACE inhibitor alone) - alternative to ACE inhibitor in intolerant patients

How are antihypertensive drugs chosen for patients?

1. Thiazide diuretic - effective, safe history and few side effects 2. If thiazide ineffective - add ACE inhibitor or calcium antagonist 3. Until recently B-blockers were first line choice but now: - less effective at reducing risk of stroke - more side effects

What is hypertension?

Blood pressure is above normal level