ADRENERGIC ANTAGONISTS adrenergic blockers 1 Nonselective 2 Selective

ADRENERGIC ANTAGONISTS

α – adrenergic blockers 1. Nonselective 2. Selective phentolamine, tolazoline, phenoxybenzamine α 1 – blocker prazosin, doxazocin, terazosin, tamsulosin, indoramin b) α 2 – blocker yohimbine 3. Miscellaneous ergot alkaloids a)

Pharmacological actions

Cardiovascular effects blocks α 1 receptor vasodilatation ↓ peripheral resistance ↓ venous return & CO HYPOTENSION

Cardiovascular effects HYPOTENSION stimulate baroreceptor reflex sympathetic discharge stimulates 1 receptor TACHYCARDIA

Cardiovascular effects blocks α 2 receptors promotes neuronal release of NE TACHYCARDIA

Other effects Nasal stuffiness -due to vasodilatation & congestion of nasal mucosa ? Miosis - due to loss of tone of radial muscle of iris ? Improved urine flow - due to smooth muscle relaxation of bladder & prostate ? Failure of ejaculation & impotence - due to inhibition of contraction of vas deferens & ejaculatory ducts ? Nausea, vomiting, diarrhea - due to ↑ in gastric secretions ?

Adverse effects Palpitation N Postural hypotension N Nasal blockade N Diarrhea N Impotence N Edema N

Phenoxybenzamine ¬ Nonselective ¬ Used α blocker in pheochromocytoma, secondary shock, peripheral vascular disease Hypotension N Flushing N Tachycardia N N Nasal congestion

Phentolamine l Non selective l Shorter duration of action l Pheochromocytoma, control of hypertension due to clonidine withdrawal, cheese reaction…

Prazosin Ø Selective α 1 blocker Inhibita phosphodiasterase - vasodilation Ø Used in hypertension & CHF Ø Postural Hypotension N Flushing N Tachycardia N N Nasal congestion

Tamsulosin w Selective α 1 A blocker w Used in Benign Prostatic Hypertrophy (BPH) Failure of ejaculation N Dizziness N

Why Tamsulosin is preferred over Prazosin in BPH even though both are selective α 1 blockers?

Therapeutic uses l Pheochromocytoma l Hypertension l Benign hypertrophy of prostate l Peripheral vascular disease