Alpha Blockers and Calcium Channel Blockers

Question 1

Alpha 1 receptors

Answer 1

Post-synaptic

Acts to vasoconstrict and increase BP

Question 2

Alpha 2 receptors

Answer 2

Pre- and post-synaptic

Inhibit norepinephrine and insulin release

Question 3

Alpha blocker effects

Answer 3

Alpha 1 antagonism (vasodilation, hypotension)

Alpha 2 antagonism (increased NE release)

Question 4

Alpha 1 antagonist example

Answer 4

Doxasozin

Tamsulosin (aplha1a specific)

Question 5

Alpha 2 antagonist example

Answer 5

Yohimbine

Question 6

Combined antagonist

Answer 6

Phenoxybenzamine

Question 7

Alpha blocker indications

Answer 7

Hypertension (useful in combo therapy)

Prostatism

Question 8

Doxasozin

Answer 8

Reversible non-specific alpha 1 blocker
Vasodilator by blocking tonic sympathetic activity on resistance vessels and reduces prostatic symptoms
Taken orally, first pass hepatic metabolism produces active metabolites
Mainly fecal elimination

Question 9

Adverse effects of alpha blockers

Answer 9

Hypotension (dizziness)
Nasal stuffiness
Dry mouth
Urinary incontinence

Question 10

Labetalol

Answer 10

Combined alpha/beta blocker
Reversible antagonist
Used for hypertension in pregnancy

Question 11

Tamsulosin

Answer 11

Specific alpha1a blocker
Oral competitive antagonist
Relaxes bladder and prostate smooth muscle so relieves prostatism
Less postural hypotension

Question 12

Calcium channel blocker indications

Answer 12

Hypertension
Angina
Arrhythmia (SVT and AF for rate only)
Vasospasm e.g. Raynaud’s

Question 13

Calcium channel blocker mechanism

Answer 13

Block L-type Ca+2 channels on cardiac tissue (decreasing contractility and sinus node rate/AV transmission) and vascular smooth muscle (decreasing tone, peripheral vascular resistance, BP and afterload)

Question 14

Dihydropyridines

Answer 14

E.g., felodipine, nifedipine
Act on resistance vessels
Can cause flushing, headaches and oedema

Question 15

Bendothiazepine

Answer 15

E.g., diltazem

Both cardiac depressant and vasodilator actions, but less so than other Ca+2 channel blockers

Question 16

Phenylalkylamine

Answer 16

E.g., verapamil

Acts on cardiac tissue as a negative inotrope (useful for angina) and the gut (can cause constipation)

Question 17

Calcium channel blocker pharmacokinetics

Answer 17

All can be oral, diltiazem and verapamil can be IV
Significant first pass hepatic metabolism via CYP450s
Variable half lives

Question 18

Nifidepine uses

Answer 18

Hypotension

Vasospasm

Question 19

Diltiazem uses

Answer 19

Angina
Hypertension
Tachyarrythmias and AF rate control

Question 20

Verapamil uses

Answer 20

Tachyarrythmias and AF rate control

Hypertension

Question 21

Verapamil major interaction

Answer 21

B-blockers – do not use together

Also take care with statins and digoxin

Question 22

Adverse effects of calcium channel blockers

Answer 22

Flushing
Headache
oedema
Negatively inotropic
Constipation

Question 23

When should alpha blockers be used?

Answer 23

3rd line treatment
In combo with ACEi and diuretic
Consider if concurrent prostatism

Question 24

When should calcium channel blockers be used?

Answer 24

2nd or 3rd line treatment
In combo with ACEi and diuretic
Use if concurrent angina, rate control or SVT control