Beta blockers

Question 1

what drug class is Labetalol

Answer 1

mixed competative alpha/beta antagonist

Question 2

mechanism of action of labetalol

Answer 2

Non selective B1/B2 blocker and alpha blocker.

B1 blockade = -ve inotropy, -ve chronotropy, reduced BP, reduced myocardial O2 demand

B2 blockade = increased PVR, bronchospasm, increased uterine tone (effects are weaker)

alpha1 blockade - reduced PVR, reduced afterload

Question 3

administration and absorption of labetalol

Answer 3

Oral or IV
better absorbed IV
Onset 20-90mins

Question 4

distribution and metabolism of labetalol

Answer 4

50% protein bound
t1/2 - 3-4 hours
hepatic clearance

Question 5

examples of non selective Beta blockers

Answer 5

propanolol, sotalol, timolol, cardevolol

Question 6

examples of beta 1 selective beta blockers

Answer 6

atenolol, bisoprolol, emolol, metoprolol

Question 7

general mechanism of action of beta blockers

Answer 7

Binds GPCR Beta 1 receptors
blocks cAMP
reduces Ca intracellularly
reduced contractility
reduced O2 demand
negative inotropy

reduces automatic self depolarisation in pacemaker cells
increases AV refractory period
negative dromotropy

Question 8

mechanism of action of sotalol

Answer 8

Class II and Class III antiarrhytmic

Non selective beta blocker
Potassium channel blocker
(can prolong QTc via K)

Question 9

75 year old man presents to the ED with central chest pain which radiates to the back and has a tearing like quality. Diagnosis of aortic dissection is made. The patient is hypertensive, heart rate 100/min. Your choice of drug for the management of hypertension is?

A Verapamil
B Metoprolol
C Sodium Nitroprusside
D Captopril

Answer 9

B Metoprolol

Vasodilators such as nitroprusside may be added for further antihypertensive treatment after successful administration of a negative inotrope. Adequate β-receptor or calcium channel blockade should be achieved prior to starting a vasodilator.