ATENOLOL

“TENORMIN”

1) Therapeutic drug action & mechanism(pharmacology)

• Selective b1-receptor blocker [actually only modestly selective)

• Occupies b-receptors and competitively reduces receptor occupancy by catecholamines and other b-agonists

• Lowers BP in patients with hypertension

• Action as antiarrythmic [classII], antianginal and antihypertensive

2) Indications

• Safer to use than longer acting antagonists in critically ill patients that require b-blockade

• Useful in controlling supraventricular arrythmias [by increasing AV nodal refractory period thereby slowing ventricular response to atrial flutter & atrial fibrillation], perioperative hypertension & MI in acutely ill patients

• Can also reduce VEB’s especially if irritability of heart due to catecholamines

• Increase stroke volume in obstructive cardiomyopathy [reduced ventricular ejection & decreased ventricular outflow resistance]

• Reduce systolic BP in dissecting aortic aneurysm

• May be effective in facilitating defibrillation

3) Effects on organs—side effects

• Negative inotrope & chronotrope; reduces MVO2

• Although selective b1-receptor blocker, may still blockadebronchial smooth muscle b2-receptor resulting in possible increased airway resistance

• b2-mediated vasodilation may be blocked resulting in a rise in SVR

• b2-receptor antagonism may impair recovery from hypoglycaemia

4) Toxic effects/ precautions with administration

5) Contraindications

• Should be avoided in asthmatics

• Diabetes and peripheral vascular disease are best treated with a selective b1-antagonist such as atenolol

• Give with caution to patients with abnormal myocardial function [eg MI or CCF] as cardiac output may be dependent on sympathetic drive resulting in cardiac decompensation

• Right ventricular failure secondary to pulmonary hypertension

• Significant right ventricular hypertrophy

• Heart blocks and bradycardias

6) Reversal, antagonism or antidote

• Bradycardia: atropine to block vagus followed by isoprenaline

• Hypotension: noradrenaline ± glucagon [direct stimulatory effect on heart bypassing adrenergic receptors]

7) Loading dose, maintenance dose, frequency & method of administration

• 5mg/10 ml ampules: 015 mg/kg over 20 min

8) Drug’s metabolism—Drug’s excretion—Half life (pharmacokinetics)

• Half life: 6 - 9 hours

• 80% excreted via kidneys

9) Important drug interactions

• Use with caution with other agents that cause myocardial depression [eg antiarrythmics and anaesthetic gases]