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What is Uroselective a1A blocker: and explain in detail?
Ans. C. Tamsulosin. (Ref. KDT 6th/pg. 119, 121, 132, 135)Tamsulosin is an Uroselective a1A blocker (a1A: a1B affinity 7-38 fold) has been found as effective as terazosin in improving BHP symptoms. Because a1A subtype predominates in the bladder base and prostate, while a1B receptors are dominant in blood vessels, tamsulosin does not cause significant changes in BP or HR at doses, which relieve urinary symptoms. No increase in adverse CVS events, including postural hypotension has been noted. Dizziness and retrograde ejaculation are the only significant side effects. Its plasma t1/2 is 6-9 hrs, but modified release cap needs once daily dosing.Terazosin# It is chemically and pharmacologically similar to prazosin; differences are- higher bioavailability (90%) and- longer plasma t1/2 (~12 hr); a single daily dose lowers BP over 24 hrs.# Though terazosin equally blocks a1A, a1B and a1D subtypes (like prazosin), it is more popular for BHP due to single daily dose.Indoramine and Urapidil are selective a1 blockers chemically distinct from prazosin; are being used as antihypertensive in some countries.a ADRENERGIC BLOCKING AGENTS CLASSIFICATIONI. Nonequilibrium type(i) b-Haloalkylamines-Phenoxybenzamine.II. Equilibrium type (competitive)A. Nonselective(i) Ergot alkaloids - Ergotamine, Ergotoxine(ii). Hydrogenated ergot alkaloids - Dihydroergotamine6 (OHE), Dihydroergotoxine(iii) Imidazolines - Tolazoline, Phentolamine(iv). Miscellaneous - Chlorpromazine, KetanserinB. a1 selective - Prazosin, Terazosin, Ooxazosin, TamsulosinC. a2 selective - Yohimbine