Monday, March 9, 2015

beta blocker

beta blockers




why we said our blood pressure will increase after exercise or when we're getting nervous?

this is because when we get nervous, our body sympathetic nerves system will secrete hormones epinephrine/ norepinephrines (which both comes under catecholamine category) into bloodstream.

These two hormones will travel in bloodstream and target on the beta 1- adrenergic receptor which is located in heart. This receptor stimulation will in turn cause:
1. positive inotropic = increase force of contraction
2. positive chronotropic = increase heart rate
3. increase cardiac conduction velocity and automaticity
Not only heart, beta 2 receptor also located in kidney.
Epinephrine and norephinephrine hormone will stimulate release of renin in the kidney.
Renin will catalyse the conversion of angiotensiongen--> angiotension I; and then angiotension II.
In the end, it will cause vasoconstriction --> lead to rise in BP.

SUMMARY
Beta 1 receptor stimulation --> cardiac stimulation and lipolysis
Beta 2 receptor stimulation --> bronchodilation and blood vessels relaxation (usually skeletal muscles)

***Cardioselective beta blockers will act on beta 1 receptor BUT its selectivity will be LOST in high dose.

Beta Blockers

1. Cardioselective B1 blockers

end with -LOL

"Betablockers Acting Exclusively AMyocardium"
ABEAM
A - AcebuteLOL
B - BetaxoLOL
E - EsmoLOL
A - AtenoLOL
M -MetaproLOL

Beta-blockers: nonselective beta-blockers "Tim Pinches His Nasal Problem" (because he has a runny nose...):
Timolol
Pindolol
Hismolol
Naldolol
Propranolol

Beta blockers: B1 selective vs. B1-B2 non-selective A through N: B1 selective: Acebutalol, Atenolol, Esmolol, Metoprolol.
O through Z: B1, B2 non-selective: Pindolol, Propanalol, Timolol.



Clinical apps of beta blockers
1. ANGINA
2. ARRHYTHMIA
3. HYPERTENSION

other considerations
1, Contraindicated in ASTHMATIC patients.
   - as beta blocker impair the relaxation of bronchial smooth muscles.
   - when beta receptor stimulated --> activate SNS --> heart contract and beat more --> BP increases.
   - At the same time, bronchial smooth muscles also get relaxed so that more oxygen in the lungs can be diffused into bloodstream to compensate the oxygen demand in out body.

2. Topical-->Treat glaucoma --> decrease intraocular pressure by decrease aqueous humor secretion. But it can diffuse into blood stream and cause systemic effects.
3. Since they lower HR and reduce tremor, used by Olympics marksmen to enhance performance BUT banned.



Beta-blockers: main contraindications, cautions
ABCDE:
Asthma
Block (heart block)
COPD
Diabetes mellitus
Electrolyte (hyperkalemia)




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