Adrenergic Receptor as part of ANS

Adrenergic Receptor as part of ANS

Actions of Adrenoceptors

Beta-1 adrenergic receptor Located on the myocytes of the heart Specific actions of the β1 receptor include: 0 Increase cardiac output, by 0 raising heart rate (positive chronotropic effect), 0 increasing impulse conduction (positive dromotropic effect), and 0 increasing contraction (positive inotropic effect), 0 thus increasing the volume expelled with each beat (increased ejection fraction). 0 Salivary Gland 0 Amylase secretion

Biochemistry of β-adrenergic 2 nd messenger - Stimulation of Adenly cyclase and camp receptors Agonists Dobutamine Antagonists Atenolol (the ***lol s)

Action of Beta blockers Reduce the activation of beta adrenergic receptors 0 Achieved by: 0 Antagonism of adrenaline and noradrenaline at the beta-adrenergic receptors 0 Specificity is important 0 Beta-1 antagonism acts on the myocytes to reduce cardiac output

Reasons to use β-blockers 0 Vascular problems as a vasoactive drug 0 Controlling hypertension 0 Cardiac function 0 Angina 0 Myocardial Infarction 0 Cardiac Arrhythmia 0 Heart Failure 0 Other 0 Thyroid surgery, glaucoma, anxiety

Hypertension

MoA not fully understood. 0 CO 0 Alter baroceptor reflex sensitivity 0 Block peripheral adrenoceptors. 0 Some beta-blockers depress plasma renin secretion. 0 Central effects may also partly explain their mode of action. Beta-blockers are effective for BP but other antihypertensives are usually more effective for reducing the incidence of stroke, MI, and CV mortality. Other antihypertensives are therefore preferred for treatment of uncomplicated HTN.

Controlling the Pressure - physiology Neural Hormonal Local factors Stroke Volume Heart Rate Peripheral Vascular Resistance Blood volume Blood Pressure

Where does β-blocker fit in?

Angina 0 MoA- 0 Sympathetic inotropic effect of heart 0 cardiac work (can t be augmented above basal levels) 0 Oxygen demand 0 exercise tolerance + myocardial stress 0 Symptomatic relief + risk of ischemic attack. 0 Sudden withdrawal may cause an exacerbation of angina. 0 There is a risk of precipitating heart failure when beta-blockers and verapamil are used together in established IHD.

Myocardial Infarction 0 Some beta-blockers can reduce the recurrence rate of MI, and early mortality following an MI. 0 However, uncontrolled heart failure, hypotension, bradyarrhythmias, and obstructive airways disease render beta-blockers unsuitable in some patients following a MI. 0 Sudden cessation of a beta-blocker can cause a rebound worsening of myocardial ischaemia.

Cardiac Arrhythmia 0 MoA- Attenuate the effects of the sympathetic system on automaticity and conductivity within the heart. 0 Afib- Can be used in conjunction with digoxin to control the ventricular response, especially in patients with thyrotoxicosis. 0 Supraventricular tachycardias- Used to control these followingmi. 0 Sotalol, a non-cardioselective beta-blocker with additional class III anti-arrhythmic activity, is used for 0 prophylaxis in paroxysmal supraventricular arrhythmias. It also suppresses ventricular ectopic beats and non-sustained ventricular tachycardia. However, it may induce torsade de pointes in susceptible patients.

Heart Failure 0 MoA- Block sympathetic activity. 0 Sympathoactivation contributes to the progression of CHF- trigger arrhythmias, increase O2 consumption, enhance hypertrophy. 0 Bisoprolol and carvedilol reduce mortality in any grade of stable heart failure. 0 Test tolerability, use low dose.

Other uses 0 Thyrotoxicosis - Beta-blockers are used in pre-operative preparation for thyroidectomy. The thyroid gland is rendered less vascular thus making surgery easier. Administration of propranolol can reverse clinical symptoms of thyrotoxicosis within 4 days. TFTs remain unaltered. 0 Pheochromocytoma- Used to control HR (should never be used alone as betablockade without concurrent alpha-blockade- may lead to a hypertensive crisis). 0 Anxiety- Alleviate some symptoms (palpitation, tremor, and tachycardia) without affecting alertness. 0 Migraine- Prophylaxis. 0 Glaucoma- Topical use ( production of aqueous humor).

Passage through the body (pharmacokinetics)

Differences among beta blockers

The good, the bad and the dreadful

Precautions & Contraindications 0 Beta-blockers slow the heart and can depress the myocardium; 0 Contra-indicated in patients with 2 nd or 3 rd heart block. 0 Should be avoided in patients with worsening unstable heart failure; 0 care is required when initiating treatment in those with stable heart failure. 0 Sotalol may prolong the QT interval 0 Particular care is required to avoid hypokalaemia in patients taking sotalol.

Precautions & Contraindications 0 Beta-blockers can precipitate bronchospasm. 0 Should usually be avoided in patients with a history of asthma. When there is no suitable alternative, it may be necessary for a patient with well-controlled asthma, or COPD 0 A cardioselective beta-blocker should be selected and initiated at a low dose by a specialist; the patient should be closely monitored for adverse effects. 0 Atenolol, bisoprolol, metoprolol, nebivolol, and (to a lesser extent) acebutolol, have less effect on the beta2 (bronchial) receptors and are, therefore, relatively car-dioselective, but they are not cardiospecific.

Precautions & Contraindications 0 Diabetes- Suppress hypoglycemia counterregulation (hepatic glucose release); Mask warning signs of hypoglycemia 0 Beta-blockers should be avoided altogether in those with frequent episodes of hypoglycaemia. 0 Pregnancy- May cause IUGR, neonatal hypoglycaemia and bradycardia; 0 The use of labetalol in maternal hypertension is not known to be harmful, except possibly in the first trimester. 0 If beta-blockers are used close to delivery, infants should be monitored for signs of betablockade 0 Breast-feeding- 0 Infants should be monitored as there is a risk of possible toxicity due to betablockade, but the amount of most beta-blockers present in milk is too small to affect infants. 0 Acebutolol, atenolol, nadolol, and sotalol are present in milk in greater amounts. The manufacturers of celiprolol, esmolol, and nebivolol advise

Side effects (Hazardous when continuous activation of beta-receptors is needed to maintain function) 0 Bradycardia 0 Bronchospasm 0 Fatigue 0 Coldness of the extremities (alpha mediated) 0 Sleep disturbances with nightmares. 0 Hypoglycemia, hyperglycemia 0 Hypoglycemia insensitivity

100 drugs list- Atenolol Indications and Dose (PO) 0 Hypertension, 25 50 mg daily (higher doses rarely necessary) 0 Angina, 100 mg daily in 1 or 2 doses 0 Arrhythmias, 50 100 mg daily 0 Migraine prophylaxis [unlicensed], 50 200 mg daily in divided doses (IV) 0 Arrhythmias, 2.5 mg at a rate of 1 mg/minute, repeated at 5-minute intervals to a max. of 10 mg. Excessive bradycardia can be countered with IV Atropine sulphate 0.6 2.4mg. 0 Arrhythmias, 150 micrograms/kg over 20 minutes, repeated every 12 hours if required. 0 Early intervention within 12 hours of myocardial infarction- IV injection over 5 minutes, 5 mg, then by mouth, 50 mg after 15 minutes, 50 mg after 12 hours, then 100 mg daily

100 drugs list- Atenolol Cautions 0 Avoid abrupt withdrawal especially in ischaemic heart disease. 0 1 st ⁰ AV block. 0 Portal hypertension (risk of deterioration in liver function). 0 Diabetes. 0 History of obstructive airways disease (introduce cautiously and monitor lung function). 0 Myasthenia gravis. 0 Symptoms of hypoglycaemia and thyrotoxicosis may be masked. 0 Psoriasis. 0 History of hypersensitivity may increase sensitivity to allergens and result in more serious hypersensitivity response, also may reduce response to adrenaline.

100 drugs list- Atenolol Contra-indications 0 Asthma. 0 Uncontrolled heart failure, Prinzmetal s angina, marked bradycardia, hypotension, sick sinus syndrome, 2 nd or 3 rd ⁰ AV block, cardiogenic shock, metabolic acidosis, severe peripheral 0 arterial disease. 0 Phaeochromocytoma (apart from specific use with alpha-blockers). 0 History of asthma or bronchospasm (when there is no alternative, a cardioselective beta-blocker can be given)/

100 drugs list- Atenolol Side-effects 0 hypoglycemia, hyperglycemia 0 GI disturbances 0 Bradycardia, heart failure, hypotension, conduction disorders, peripheral vasoconstriction (including exacerbation of intermittent claudication and Raynaud s phenomenon). 0 Bronchospasm, dyspnoea. 0 Headache, fatigue, sleep disturbances, paraesthesia, dizziness, vertigo, psychoses. 0 Sexual dysfunction. 0 Purpura, thrombocytopenia. 0 Visual disturbances. 0 Exacerbation of psoriasis, alopecia. 0 rarely rashes and dry eyes (reversible on withdrawal).