B-blockers

Question 0

Labetolol

Answer 0

1. Competitive antagonist at a1 and B adrenergic receptors
2. It is metabolized by liver—>clearence is affected by hepatic perfusion
3. Dose: 5-10 mg every 5 min or infusion of 2 mg/ min
4. Comes in vial of 5 mg/ ml
5. Useful in patients with aortic dissection or hypertensive crisis bc vasodilation is not accompanied by tachycardia
6. It can be given for tx of hypertension in pregnancy bc it does not effect uterine blood flow
7. It can also be given to cardiac patients

Question 1

Esmolol

Answer 1

1.Short half life: 9-10 min
A. Why short half life bc it is hydrolyzed by blood- born esterase
B. cardioselective
C. Peak effect of loading dose is 5-10 min diminishes within 20-30 min
Note: good for critically ill patients in whom adverse effect of bradycardia, hypotension or heart failure may require rapid removal of drug
D.it can be given as a bolus 0.5 mg/ kg
It can be given as an infusion
E. When we use it to treat supra ventricular tachycardia
Bolus of 500 mcg/ kg given over 1 min, followed by infusion of 50
Mcg/ kg/ min for 4 min
If heart rate is not controlled u give a bolus dose of 500 mcg/ kg
/ min followed by 100 mcg/ kg/ min for 4 min if this doesn’t work
U keep increasing ur infusion dose by 50 mcg/ kg/ min up to
200-300 mcg/ kg/ min
F. It is safe to use for treatment of intraoperative and post operative
Tachycardia, and hypertension

Question 2

Metoprolol

Answer 2

Metoprolol:
Cardioselective B adrenergic blocker
Usage: angina lector is and MI bc it decreases cardiac output reduces oxygen demands of the heart
Onset: immediate, peaks in 20 min duration 5-8 hours
Dosage: 2.5-5 mg every 2-5 min up to 15 mg with titration to heart and BP

Question 3

Propranolol

Answer 3

1. Non selective B blocker
2. Effects both B1 and B2
3. Highly lipid soluble and it is metabolized by the liver—> liver disease or altered hepatic perfusion can effect the metabolism
4. Dose: 0.25-0.5 mg/ kg titrate to effect

Question 4

What are the most commonly used B-blockers in anesthesia? And y?

Answer 4

Esmolol, labetolol, metoprolol, propranolol

Reason-: they r available in intravenous form

Question 5

What r the most important difference btw the B-blockers?!

Answer 5

Duration of action and cardioselectivity

Question 6

Cardioselective B blockers:

Answer 6

1. Esmolol, metoprolol
2. They have higher selectivity for B1 than B2.
3. With blockade of B1 velocity of av conduction, heart rate and cardiac contractility decreases
4. Renin secretion as well as lipolysis also decreases
5. At higher doses the select invests for B1 is lost and we have B2 blockade as well with potential for bronchocobstriction, peripheral vasoconstriction and decreased glycogenolysis

Question 7

Adverse effects of b- adrenergic blockade

Answer 7

1. Bradycardia, hypotension, a systole
2. Decrease in contractility may cause CHF( when heart can not pump adequate blood to maintain blood flow to meet body’s demands) in patients with compromised cardiac function
3. Diabetes is relative contradiction in long term use of B blockers bc B- blockers will mask the warning signs of hypoglycemia ( tachycardia and tremors, and glycogenesis is blunted
4. use of B- blockers in patients with pheochromocytomas should be avoided unless a receptor has been blocked (pheochromocytoma (from Greek phaios “dark”, chroma “color”, kytos “cell”, -oma “tumor”) or phaeochromocytoma (PCC) is a neuroendocrine tumor of the medulla of the adrenal glands (originating in the chromaffin cells), or extra-adrenal chromaffin tissue that failed to involute after birth[1] and secretes high amounts of catecholamines, mostly norepinephrine, plus epinephrine to a lesser extent.[2] Extra-adrenal paragangliomas (often described as extra-adrenal pheochromocytomas) are closely related, though less common, tumors that originate in the ganglia of the sympathetic nervous system and are named based upon the primary anatomical site of origin)

Question 8

How to reverse the over dose of B blockers?

Answer 8

Atropine, however in order to maintain adequate rate of contraction isoproternol, doubtamine and glucagon may need to be added

Question 9

Drug interaction

Answer 9

B-blocker+ verapamil: rate of contractility of verapamil is additive to b blockers

B- blockers and digoxin: have powerful effect on rate and conduction

Question 10

Atropine

Answer 10

Atropine is a competitive muscarinic acetylcholine receptor antagonist
In general, atropine counters the “rest and digest” activity of glands regulated by the parasympathetic nervous system. This occurs because atropine is a competitive antagonist of the muscarinic acetylcholine receptors (acetylcholine being the main neurotransmitter used by the parasympathetic nervous system). Atropine dilates the pupils, increases heart rate, and reduces salivation and other secretions.

Question 11

Isoproternol

Answer 11

Isoprenaline (INN) or isoproterenol (USAN, trade names Medihaler-Iso and Isuprel) is a medication used for the treatment of bradycardia (slow heart rate), heart block, and rarely for asthma. It is a non-selective beta-adrenergic agonist and structurally similar to adrenaline.[1]