Antiadrenergic drugs
Dr. Karun Kumar
Senior Lecturer
Dept. of Pharmacology

General Effects of α blockers
Blockade of vasoconstrictor α1 receptors
↓
↓ TPR
↓
Pooling of blood in capacitance vessels
↓
↓ venous return and CO
↓
Fall in BP

Interference in postural reflex
↓
Hypotension
↓
Dizziness and syncope
• Patients receiving an α blocker should not suddenly
stand up after being supine on the dental chair
• Reflex tachycardia occurs (↓ mean arterial pressure
and ↑ NA due to blockade of presyn α2 receptors)

• Nasal stuffiness and miosis
Hypotension ↓ renal blood flow
↓
↓ GFR & ↑ reabs. of Na+ and water
↓
Na+ retention & expansion of blood volume
(accentuated by reflex ↑ in renin)

Tone of smooth muscle in bladder trigone, sphincter
and prostate ↓ by blockade of α1 receptors
↓
Urine flow in patients with benign hypertrophy of
prostate (BHP) is improved
• Contractions of vas deferens and related organs
which result in ejaculation are coordinated through
α rec. (α blockers can inhibit ejaculation 
impotence)

Side Effects

Uses of α blockers
1. Pheochromocytoma  Phenoxybenzamine
definitive therapy for inoperable and malignant
tumors.
• Employed before and during surgical removal of the
tumor
• Alternatively, Phentolamine drip can be instituted
during the operation.

2. Hypertension  Prazosin and other slective α1
blockers are useful antihypertensive drugs.
• Phentolamine helps to control episodes of ↑ BP
during Clonidine withdrawal and cheese reaction in
patients on MAO inhibitors

Cheese Reaction (DOC  Phentolamine)
Cheese, beer, red wine & banana contain tyramine
↓
In presence of MAOI, it escapes degradation
↓
Reaches systemic circulation
↓
Uptake by adrenergic neuron
↓
Enters storage vesicles & displaces NE
↓
Hypertensive crisis

3. Benign hypertrophy of prostate (BHP)  The
urinary obstruction caused by BHP has a static
component (↑ size of prostate) and a dynamic
component (↑ tone of bladder neck/prostate s.m.)
Two classes of drugs are available:
1. α1 adrenergic blockers (Prazosin like)  Decrease
tone of prostatic/bladder neck muscles.
2. 5-α reductase inhibitor (Finasteride)  Arrest
growth/reduce size of prostate

Classification

Uses of β blockers (THAPPAD)
1. Thyrotoxicosis & Tremors
2. HTN & Hypertrophic cardiomyopathy
3. Angina & Acute MI
4. Prophylaxis of migraine
5. Phaeochromocytoma (along with alpha blockers)
6. Anxiety & Arrhythmias
7. Dissecting aortic aneurysm
8. Digitalis toxicity

Adverse effects of beta blockers
(BBC Loses Viewers in Rochedale)
• Bradycardia
• Bronchoconstriction
• Claudication
• Lipids (profile altered)
• Vivid dreams & nightmares
• Negative inotropic action
• Reduced sensitivity to hypoglycemia

Contraindications of Propranolol
• Don’t Prescribe Him Propranolol
1. Diabetes mellitus
2. Pulmonary diseases (Asthma, COPD)
3. Heart block, bradycardia
4. Prinzmetal’s angina
5. Peripheral vascular disease

Drug Interactions
1. Additive depression of SAN & A-V conduction
with Digitalis and Verapamil  Cardiac arrest
2. Propranolol delays recovery from hypoglycaemia
due to insulin and oral antidiabetics. Warning
signs of hypoglycaemia (tachycardia, tremor) are
suppressed
3. Phenylephrine, Ephedrine and other α agonists
present in cold remedies can cause marked rise in
BP in β blocked subjects

4. Though only low concentrations of Adr are added
to lidocaine for dental anesthesia, it may produce
some pressor action in patients receiving
nonselective β blockers
5. Indomethacin and other NSAIDs attenuate the
antihypertensive action of β blockers
6. Propranolol retards lidocaine metabolism by
reducing hepatic blood flow

Other β Blockers
• Cardioselective (Metoprolol, Atenolol, Acebutolol,
Bisoprolol, Nebivolol)
1. Lower propensity to cause bronchoconstriction
2. Less interference with carbohydrate metabolism
3. Lower incidence of cold hands and feet
4. No/less deleterious effect on blood lipid profile
5. Ineffective in suppressing essential tremor
6. Less liable to impair exercise capacity

Partial agonistic (intrinsic
sympathomimetic) (Pindolol, Acebutolol)
• Activate β1 and/or β2 receptors submaximally
1. Bradycardia and depression of contractility at rest
are not prominent
2. Withdrawal is less likely to exacerbate
hypertension or angina
3. Not effective in migraine prophylaxis— dilate
cerebral vessels
4. Less suitable for secondary prophylaxis of MI

α + β Adrenergic blockers
• Labetalol  5 times more potent in blocking β than
α receptors
• Causes ↓ BP & no/slight ↓ in HR
• Orally effective but undergoes considerable first
pass metabolism
• Moderately potent hypotensive & is specially useful
in pheochromocytoma, clonidine withdrawal; can
also be used in essential hypertension
• S/E  Postural hypotension

• Carvedilol  β1 + β2 + α1 blocker; produces
vasodilatation due to
1. α1 blockade
2. Calcium channel blockade
• Has antioxidant property
• Use  Hypertension & CHF