Beta blockers Pharmacology
-
Upload
dr-pramod-b -
Category
Health & Medicine
-
view
619 -
download
0
Transcript of Beta blockers Pharmacology
β blockers
β receptor actions
• Dilatation of arterioles and veins → fall in BP (β2)• Cardiac stimulation (β1), ↑ rate, force and
conduction velocity• Bronchodilatation (β2)• Enhanced aqueous secretion
β receptor actions
• Liver—glycogenolysis (β2) → hyperglycaemia
β receptor actions
• Fat—lipolysis (β1 + β2 + β3) → increased blood FFA, calorigenesis.
β receptor actions
• Renin release from kidney (β1)
Β Receptor locationReceptor Locationβ1 Heart, JG cells in kidneyβ2 Bronchi, blood vessels, liver, skeletal muscle
β3 Adipose tissue
TISSUE RECEPTORTYPE
ACTION
Heart • Sinus and AV • Conduction pathway • Myocardial fibrils
β1β1β1
AutomaticityConduction velocity, automaticityContractility, automaticity
Vascular smooth muscle β2 Vasodilation
Bronchial smooth muscle β2 Bronchodilation
Kidneys β1 Renin release
Liver β2 Glycogenolysis and gluconeogenesis
Adipose tissue β3 Lipolysis
Skeletal muscle β2 Tremor
Comparison of agonists and antagonists at β Receptor
Classification of β-blockers• Nonselective (β1 and β2)• a. Without intrinsic sympathomimetic activity• Propranolol, Sotalol, Timolol.• b. With intrinsic sympathomimetic activity• Pindolol• c. With additional α blocking property• Labetalol, Carvedilol
• Cardioselective (β1)• Metoprolol, Atenolol, Acebutolol, Bisoprolol, Esmolol, Betaxolol,
Celiprolol, Nebivolol
Propranolol: A nonselective β antagonist
• Prototype β-adrenergic antagonist• Blocks both β1 and β2 receptors with equal affinity.
Cardiovascular effects of Propranolol
• Negative inotropic and chronotropic effects .• Directly depresses sinoatrial and atrioventricular
nodal activity. • Cardiac output, workload, and oxygen consumption
are decreased by blockade of β1 receptors.
Vascular effects of Propranolol
• Peripheral vasoconstriction• Nonselective blockade of β receptors prevents β2-
mediated vasodilation in skeletal muscles, increasing peripheral vascular resistance.
Effects of Propranolol on bronchial smooth muscle
• Bronchoconstriction• Blocking β2 receptors in the lungs causes contraction
of the bronchiolar smooth muscle.• β-blockers, particularly, nonselective ones, are
contraindicated in patients with COPD or asthma.
Effects of Propranolol on glucose metabolism
• Disturbances in glucose metabolism• β blockade leads to decreased glycogenolysis and
decreased glucagon secretion.• Therefore, if propranolol is given to a diabetic patient
receiving insulin, careful monitoring of blood glucose is essential, because pronounced hypoglycemia may occur after insulin injection.
• β-blockers also attenuate the normal physiologic response to hypoglycemia.
Therapeutic uses of Propranolol
• Hypertension: • Decreased cardiac output is the primary mechanism • Inhibition of renin release from the kidney.• Decrease in total peripheral resistance with long-
term use.
Therapeutic uses of Propranolol
• Angina pectoris: • Propranolol decreases the oxygen requirement of
heart muscle and, therefore, is effective in reducing chest pain on exertion that is common in angina.
Therapeutic uses of Propranolol
• Myocardial infarction: • Propranolol acts by decreasing oxygen requirment to
heart muscle.
Therapeutic uses of Propranolol
• Migraine: mechanism of action unknown.
Therapeutic uses of Propranolol
• Hyperthyroidism: • Propranol acts by blunting the widespread
sympathetic stimulation that occurs in hyperthyroidism.
Adverse effects of Propranolol
• Tiredness and reduced exercise capacity: • Due to blunting of β2 mediated increase in blood
flow to the exercising muscles as well as attenuation of glycogenolysis and lipolysis.
Adverse effects of Propranolol
• Bronchoconstriction: • Due to blockade of β2 receptors on smooth muscles
of bronchi. • Therefore, propranolol is contraindicated in patients
with COPD or asthma.
Adverse effects of Propranolol
• Arrhythmias:• Treatment with β-blockers must never be stopped
abruptly because of the risk of precipitating cardiac arrhythmias, which may be severe.
Adverse effects of Propranolol
• Sexual impairment:• The reasons for this are not clear and may be
independent of β receptor blockade.
Adverse effects of Propranolol
• Metabolic disturbances:• β Blockade leads to decreased glycogenolysis and
decreased glucagon secretion. • Fasting hypoglycemia may occur. • The perception of symptoms of hypoglycemia such
as tremor, tachycardia, and nervousness are blunted by β-blockers.
Adverse effects of Propranolol
• Metabolic disturbances:• Increased low density lipoprotein (“bad”cholesterol), • increased triglycerides, • reduced high-density lipoprotein (“good”cholesterol).
Elimination half-lives for some β-blockers
Nonselective β antagonists
• Timolol • Treatment of glaucoma• Topically applied timolol is effective in diminishing
intraocular pressure in glaucoma. • This occurs by decreasing the secretion of aqueous
humor by the ciliary body.
Selective β1 antagonists
• Acebutolol, atenolol, betaxolol, bisoprolol, esmolol, metoprolol, and nebivolol.
• In contrast to propranolol, the cardioselective β-blockers have fewer effects on pulmonary function, peripheral resistance, and carbohydrate metabolism.
Therapeutic uses: The cardioselective β-blockers
• Useful in hypertensive patients with impaired pulmonary function.
Antagonists of both α and β adrenoceptors
• Labetalol and carvedilol:• Nonselective β-blockers with concurrent α1-blocking
actions that produce peripheral vasodilation, thereby reducing blood pressure.
• Uses:• Hypertensive emergencies, because it can rapidly
lower blood pressure.• Pregnancy-induced hypertension.
Thank You
Question 1• A β-blocker was prescribed for hypertension in a female
asthma patient. After about a week of treatment, the asthma attacks got worse, and the patient was asked to stop taking the β-blocker. Which of the following β-blockers would you suggest as an alternative in this patient that is less likely to worsen her asthma?
• A. Propranolol.• B. Metoprolol.• C. Labetalol.• D. Carvedilol.
Question 1• Correct answer = B. • The patient was most likely given a nonselective β-blocker
(antagonizes both β1 and β2 receptors) that made her asthma worse due to β2 antagonism.
• An alternative is to prescribe a cardioselective (antagonizes only β1) β-blocker that does not antagonize β2 receptors in the bronchioles.
• Metoprolol is a cardioselective β-blocker. • Propranolol, labetalol, and carvedilol are nonselective β-
blockers and could worsen the asthma.
Question 2
• Which of the following is correct regarding β-blockers?
• A. Treatment with β-blockers should not be stopped abruptly.
• B. Propranolol is a cardioselective β-blocker.• C. β-Blockers may cause orthostatic hypotension.• D. Cardioselective β-blockers worsen asthma.• E. β-Blockers decrease peripheral resistance by
causing vasorelaxation.
Question 2
• Correct answer = A. • If β-blocker therapy is stopped abruptly, that could
cause angina and rebound hypertension.
Question 3
• The therapeutic actions of β blockers such as propranolol in angina pectoris is believed to be primarily a result of
• A) reduced production of catecolamines• B) dilation of coronary vasculature• C) decreased requirment for myocardial oxygen• D) Increased peripheral resistance
Question 3
• Correct answer C• β blockers slows heart rate, reduce cardiac
contractility. • These hemodynamic actions decrease the
requirment of the heart for oxygen.