Sympatholytic Drugs | Classifications | Pharmacological Effects

Sympatholytic drugs block adrenergic activity, lowering blood pressure and reducing heart rate. (Also called Adrenergic Antagonists)

These drugs block the effects of the sympathetic nervous system by inhibiting adrenergic receptors.

Alpha-blockers:
- Non-selective: Phenoxybenzamine, Phentolamine
- Selective α1 blockers: Prazosin, Terazosin
Beta-blockers:
- Non-selective: Propranolol
- Selective β1 blockers: Atenolol, Metoprolol
Centrally acting sympatholytics:
- Clonidine, Methyldopa

Eye
- Miosis: Block of α1 prevents pupil dilation.
- Reduced intraocular pressure: β-blockers reduce aqueous humor production (used in glaucoma).
Cardiovascular System
- α1 blockade:
  - Vasodilation → decreased peripheral resistance → lower BP.
  - May cause reflex tachycardia.
- β1 blockade:
  - Decreased heart rate, contractility, cardiac output.
  - Useful in angina, hypertension, arrhythmias, heart failure.
- β2 blockade (nonselective):
  - Can cause vasoconstriction and worsen peripheral vascular disease.
Respiratory System
- β2 blockade: May cause bronchoconstriction, especially in asthmatics (avoid nonselective β-blockers like propranolol).
Gastrointestinal Tract
- Minimal effects usually but decreased perfusion and slowed motility may occur indirectly.
Urinary Tract
- α1 blockers (e.g., tamsulosin): Relax prostatic and bladder neck smooth muscle → improve urine flow in BPH.
- β-blockers: Minimal direct effect.
Metabolic Effects
- β-blockers:
  - Mask hypoglycemia symptoms (important in diabetic patients).
  - May decrease glycogenolysis and gluconeogenesis → caution in insulin-dependent diabetics.
  - May affect lipid profile (increase triglycerides, decrease HDL).