Antiadrenergic agents inhibit the signals of epinephrine and norepinephrine. They are primarily postsynaptic adrenergic receptor antagonists (alpha and beta adrenergic receptor antagonists, or "blockers"), inhibiting the downstream cellular signaling pathways of adrenergic receptors. However, there are exceptions: clonidine is an adrenergic agonist at the α2 receptor; since this receptor is located presynaptically, agonism at this receptor inhibits the presynaptic release of adrenaline and noradrenaline, preventing postsynaptic adrenergic receptor activation and downstream signaling.

1. Antiadrenergic or
sympatholytic drugs
• Antagonise the receptor action of adrenaline and related drugs
• Classified on the basis of receptors they block primarily
• Alpha, Beta, Both
• Classification
Alpha (α) blocker
•α1 selective
•α2 selective
•Nonselective(α1 & α2).
Beta (β) blocker
•Nonselective(b1&b2)
•Cardioselective (β1)

2. Alpha (α) blockers
α1 selective Prazosin, Terazosin,
,
α2 selective Yohimbine,
Non- selective α blocker Phenoxybenzamine,
Phentolamine,,
ergotamine,
chlorpromazine

3. alphaadrenergicblockingdrugs
•Uses:
• Pheochromocytoma
• Hypertension
(phenoxybenzamine/phentolamine)
• Benign hypertrophy of prostate
• Secondary shock
• Congestive heart failure

4. Side effects:
• Phenoxybenzamine: Postural hypotension,,
miosis, inhibition of ejaculation
• Ergot alkaloids: gangrene of toes and
fingers (ergotism)
• Prazosin and alike : postural hypotension

5. Beta adrenergic blocker
• Nonselective (beta-1 and beta -2)
• propranolol, sotalol, timolol
• pindolol
• Cardioselective (beta- 1)
• Metoprolol, Atenolol, Acebutolol, Bisoprolol,
Esmolol, Betaxolol, Celiprolol, Nebivolol
• Alpha and beta blocker : labetolol, carvedilol

6. Uses of beta blocker
• Hypertension
• Stable Angina
• Cardiac arrhythmias
• Myocardial infarction
• Congestive heart failure
• Hypertrophic obstructive cardiomyopathy
• Pheochromocytoma
• Thyrotoxicosis
• Migraine
• Anxiety
• Essential tremor
• Glaucoma