Alpha and Calcium channel blockers Flashcards
a1 receptors
- post-synaptic
- facilitate vasocontriction
- a1a = prostate
- a1b = vascular SM
- increase BP (vasoconstriction)
a2 receptors
- pre & post-synaptic
- inhibit NEP & insulin release
alpha 1 antagonism
- mechanism and examples
vasodilation
e.g. doxazosin (block all a1), tamsulosin (a1a specific)
adverse effects of alpha blockers
- hypotension (dizziness) take at night
- tiredness
- nasal stuffiness
- dry mouth
- urinary incontinence in women
doxazosin
- reversible alpha blocker (mainly a1, all subtypes)
- vasodilator
- useful in hypertension & prostatic symptoms
- long t1/2 (once daily)
- preferred a blocker
tamsulosin
- competitive a1a antagonist
- used in prostates to relax bladder & prostate SM
- less postural hypotension (little effect on BP)
- long t1/2
examples of combined alpha and beta blockers and their use
labetalol
- hypertension in pregnancy
- blocks all adrenergic receptors
carvedilol
- congestive HF
- blocks all adrenergic receptors
- also antioxidant properties
mechanism of calcium channel blockers
- block V-gated L-type Ca channels
vascular SM
- decrease arteriole SM tone
- decrease PVR
- decrease BP & afterload
cardiac cells
- decrease contractility
- decrease sinus node rate and AV node transmission
mechanism of Ca channel blockers in hypertension, angina, arrhythmias
hypertension = vasodilation
angina = decrease cardiac work, vasodilation
arrhythmias = SVT termination
also useful in vasospasm
calcium channel blocker - dihydropyridine
- examples
- site of action
- effects
e.g. nifedipine, felodipine, amlodipine
resistance vessels
drops BP
- flushing, headache, oedema
vasodilates coronaries
calcium channel blocker - phenylalkylamine
- example
- site of action
- effects
e.g. verapamil
conducting tissue
- slows HR
- negative inotrope
- blocks GI channels (constipation)
pharmacokinetics of calcium channel blockers
- form given
- half life
- metabolism
- given orally (IV preparations of diltiazem & verapamil to quickly reduce HR)
- nifedipine & diltiazem short T1/2
- amlodipine long t1/2
- significant first pass hepatic metabolism (CYP450)
nifedipine
- calcium channel blocker
- hypertension & vasospasm
- don’t give sublingually give orally
- hepatic metabolism, protein bound
- renal excretion
- oedema, flushing, headache
diltiazem
- calcium channel blocker
- angina, hypertension, rate control (AF)
- can be used with b-blockers
- oedema, flushing, headache, bradycardia
- oral and IV
verapamil
- calcium channel blocker
- rate control (AF)
- side-effects = bradycardia
- DONT use with b-blockers
- negative inotropic effect
- interferes with many drugs e.g. statins and digoxin
