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6.adrenergic blockers
1. ADRENERGIC BLOCKERS
Dr. Mahmoud H. Taleb
Assistant Professor of Pharmacology and Toxicology
Department of Pharmacology and Medical Sciences, Faculty of
Pharmacy- Al azhar University 1
2. Adrenergic blocker
(antagonists/sympatholytics)
Drug that bind to adrenoceptor but do not trigger
the usual receptor-mediated intracellular effect.
Have the opposite effect of adrenergic agents
Also known as adrenergic antagonists or
adrenergic Blocking Agents
Block alpha & beta receptor sites(nonselective)
direct or indirect acting on the release of
norepinephrine and epinephrine.
2
7. A- Non Selective Alpha Blocker
1- Phenoxybenzamine 1 > 2
Irreversible
Covalent binding with receptor
Long duration of action (14 - 48 hrs)
Also blocks 5-HT, ACh & H1 receptors
Inhibits neuronal & extra-neuronal uptake of NE
Absorbed from GIT, low bioavailability
7
8. CVS effect
• Vasodilatation – arteriolar and venous BP
• Magnitude dependent on sympathatic activity at that
time
• postural hypotension
• More marked if hypovolaemia is present
• Baroreceptor reflex activation
• reflex tachycardia
• tends to oppose the fall by HR and CO
Epinephrine reversl: All -adrenergic blockers
reverse -agonist action of epinephrine.
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9. Other Effects
↓contraction of trigone and sphincterin blood
vessels
urine flow
insulin secretion from islet cells(2 blockers)
Miosis
Nasal stuffiness
adrenergic sweating
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10. Clinical use:
Phaeochromocytoma
Control of BP
Prior to surgery
Adverse effects:
Postural hypotension
Tachycardia
Nausea & Vomiting
Nasal stuffiness
ejaculation
Contraindication: in patient with decrease
coronary infusion.
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12. 3- Tolazoline
Similar to phentolamine
Slightly less potent
Better absorption from GIT
Rapidly excreted in urine
Limited clinical application
peripheral vasospastic disease
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13. B- 1 Selective Agents
Prazosin & Terazosin 1 >>>> 2
Effective in management of hypertension
Low affinity for 2
Relative absence of tachycardia
↓ Triglycerides & LDL, ↑ HDL (favourable)
Both are extensively metabolized by liver
Prazosin shows high 1st Pass effect (50%)
Oral absorption – good
Terazosin :Bioavailability >90%; >18 h action
Uses:
• Hypertension
• BPH
Adverse effects
First dose effect
Postural hypotension
Salt & water retention ( long term use) 13
14. Doxazosin:
Similar to Prazosin but longer t ½ (22 Hr) and
inactive product excreated in feces not in urine.
Alfuzosin :
similar to prazosin
Tamsulosin
Selective α1 anatgonist
Has greater selectivity for α1A subtype
Has greater efficacy for BPH
Relatively smaller effects on blood vessels
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15. Clinical Uses Of Blockers
Pheochromocytoma
Hypertensive emergencies
Chronic hypertension – non selective blockers are not
used
Peripheral vascular diaease
spastic (Raynauds), not morphological
Local vasoconstrictor excess– phentolamine useful-
local infiltration
Urinary obstruction – BPH-prazosin, terazosin,
tamsulosin
CHF
α2- selective antagonists do not have any recognised
clinical use. 15
16. Adverse effects α1 – blockers
Postural hypotension( less with α1 selective-
vasodilatation is less)
Reflex tachycardia ( less with α1 selective)
Salt and water retention
Nasal stuffiness
Miosis
Failure of ejaculation
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22. Timolol and Nadolol
Block β1 & β2 adrenoceptor and are more potent
than propranolol.
Nadolol has a very long duration of action.
Timolol reduces the production of aqueous humor
in the eye. It is used topically in the treatment of
chronic open-angle glaucoma and, occasionally, for
systemic treatment of hypertension.
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23. Symptoms of overdose include:
abdominal irritation
central nervous system depression
coma
extremely slow heartbeat
heart failure
lethargy
low blood pressure
wheezing
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24. Selective β1 antagonists
Acebutolol, atenolol, betaxolol, bisoprolol, esmolol,
metoprolol, and nebivolol
Drugs that preferentially block the β1 receptors minimize
the unwanted bronchoconstriction (β2 effect) seen with
propranolol use in asthma patients.
Actions:
lower blood pressure in hypertension
and increase exercise tolerance in angina
Therapeutic use:
In hypertensive patients with impaired pulmonary function.
first-line therapy for chronic stable angina
Because these drugs have less effect on peripheral vascular
β2 receptors, coldness of extremities (Raynaud
phenomenon), a common side effect of β-blockers, is less
frequent. 24
26. Antagonists with partial agonist ctivity
Acebutolol and pindolol
Acebutolol (β1-selective antagonist)
pindolol (nonselective β-blocker) are not pure
antagonists.
These drugs also have the ability to weakly stimulate
both β1 and β2 receptors.
Used in hypertensive patient with moderate bradycardia.
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27. Antagonists of both α and β adrenoceptors
Labetalol and carvedilol
Labetalol and carvedilol are nonselective β-blockers
with concurrent α1-blocking actions that produce
peripheral vasodilation, thereby reducing blood
pressure.
They contrast with the other β-blockers that
produce initial peripheral vasoconstriction, and
these agents are therefore, useful in treating
hypertensive patients for whom increased
peripheral vascular resistance is undesirable.
Carvedilol also decreases lipid peroxidation and
vascular wall thickening, effects that have benefit in
heart failure. 27
28. Therapeutic use in hypertension and heart failure
Adverse effect:
Orthostatic hypotension.
Dizziness.
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29. Dr. Mahmoud H. Taleb 29
IV. DRUGS AFFECTING NEUROTRANSMITTER
RELEASE OR UPTAKE
A. Reserpine
Reserpine a plant alkaloid, blocks the Mg2+/adenosine triphosphate
dependent transport of biogenic amines, norepinephrine, dopamine,
and serotonin from the cytoplasm into storage vesicles in the
adrenergic nerves of all body tissues. This causes the ultimate
depletion of biogenic amines. Sympathetic function, in general, is
impaired because of decreased release of norepinephrine. The drug
has a slow onset, a long duration of action, and effects that persist
for many days after discontinuation.
30. B. GUANETHIDINE
Guanethidine blocks the release of stored norepinephrine
as well as displaces norepinephrine from storage
vesicles (thus producing a transient increase in blood
pressure). This leads to gradual depletion of
norepinephrine in nerve endings except for those in the
CNS. Guanethidine commonly causes orthostatic
hypotension and interferes with male sexual function.
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