These are the agents, which block the action
of adrenaline and noradrenaline. They block
either alpha or beta or both adrenergic
receptors. They are classified as in table 3.3.1
and 3.3.2.

GENERAL CHARACTERISTICS OF

ALPHA BLOCKERS

Alpha blockers are the drugs which block

the pressor response to noradrenaline and

Table 3.3.1: Classification for alpha adrenergic blocking agents.

A.Non-equilibrium

Phenoxybenzamine (FENOXENE) 20-60 mg orally, 1 mg/kg IV infusion

B.Equilibrium

I. Nonselective (ααααα 1 +ααααα 2 blockers)

i. Ergot alkaloids

Ergotamine (GYNERGEN) 1-3 mg oral, 0.25-0.5 mg IM/SC

Dihydroergotamine 2-6 mg oral, 0.5-1 mg IM

Dihydroergotoxine (HYDERGINE) 1.5 mg oral TDS, 0.15-0.6 mg IM

ii. Imidazolines

Phentolamine mesylate (FENTANOR) 50 mg QID

Tolazoline (PRISCOL) 25-50 mg TDS

iii.Phenothiazines

Chlorpromazine (LARGECTIL) 25-50 mg oral/IM

II ααααα 1 Selective

Prazosin (MINIPRESS) 0.5-1.0 mg TDS

Terazosin (OLYSTER) 2-10 mg/day, 1 mg HS

Triamazosin 25-200 mg TDS

Doxazosin (DOXACARD) 1-4 mg/day

Tamsulosin (DYNAPRES) 0.4-0.8 mg OD

III.ααααα 2 Selective

Yohimbine 2-4 mg TDS

PharmacodynamicsPharmacodynamicsPharmacodynamicsPharmacodynamicsPharmacodynamicsPharmacodynamicsPharmacodynamicsPharmacodynamicsPharmacodynamicsPharmacodynamics

Chapter

1.4

Chapter

3.3

(Antiadrenergic Agents)(Antiadrenergic Agents)(Antiadrenergic Agents)(Antiadrenergic Agents)(Antiadrenergic Agents)

SympatholyticsSympatholytics