Drug that selectively acts on AlphalA receptors (blocking action), used in treatment of Benign Prostatic Hypertrophy and has least or no cardiac side effects is:
Ans. c (Tamsulosin). (Ref. KD Tripathi 5th ed. 126)Terazosin, doxazosin and tamsulosin are the peferred al blockers for mgt of BHP because of once daily dosing.There is some evidence that terazosin and doxazosin promote apoptosis in prostate. Tamsulosin appears to cause fewer vascular side effects because of relative alA/alD selectivity.a-ADRENERGIC BLOCKING AGENTSClassification# Nonequilibrium type- b-Haloalkylamines: Phenoxybenzamine# Equilibrium type (competitive)- Nonselective* Ergot alkaloids: Ergotamine, Ergotoxineii) Hydrogenated ergot alkaloids: Dihydroergotamine,Dihydroergotoxineiii) Imidazolines: Tolazoline, Phentolamineiv) Miscellaneous: Chlorpromazine, Ketanserin- a1 selective: Prazosin, Terazosin, Oxazosin, Tamsulosin- a2 selective: YohimbineDrugFeaturesPrazosin# It is first of the highly selective a1 blockers having a1: a2 selectivity ratio 1000:1. It blocks sympathetically mediated vasoconstriction and produces fall in BP which is attended by only mild tachycardia; NA release is not increased due to absence of blockade.# Prazosin dilates arterioles more than veins.# Postural hypotension occurs, especially in the beginning dizziness and fainting as 'first dose effect'.# Subsequently tolerance develops to this side effect.# Prazosin is effective orally (bioavailability ~60%), highly bound to plasma proteins.# It is primarily used as an antihypertensive.# Other uses include:# LVF not controlled by diuretics and digitalis,# Raynaud's disease and# Benign prostatic hypertrophy (blocks a1 receptors present in bladder trigone and prostate and thus improves urine flow, reduces residual urine in bladder).Terazosin# It is chemically and pharmacologically similar to prazosin;# differences are higher bioavailability (90%) and longer plasma tl/2 (~12 hr); a single daily dose lowers BP over 24 hrs.# Though terazosin equally blocks a 1A, a 1B and ? 1D subtypes (like prazosin), it is popular for BHP due to single daily dose.Doxazosin# Another long acting (tl/2 18 hr) congener of prazosin with similar pharmacological profile, used in hypertension and BHP.Tamsulosin# Uroselective a 1A blocker (alA: alB affinity 7-38 fold)# As effective as terazosin in improving BHP symptoms.# Because a 1A subtype predominates in the bladder base and prostate, while alB receptors are dominant in blood vessels, tamsulosin does not cause significant changes in BP or HR at doses, which relieve urinary symptoms.# No adverse cardiovascular events or postural hypotension. Dizziness and retrograde ejaculation are the only side effects.# Its plasma tl/2 is 6-9 hrs, but the modified release cap needs only once daily dosing.
Terazosin
Prazosin
Tamsulosin
Doxazosin
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