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Selective α1-Blocker
Madhumita Dixit
JR-3
Pharmacology Department
Moti Lal Nehru Medical College
Prayagraj, U.P.
Prazosin
Introduction-
• Selective α1 blocker
• Affinity for α1:α2 (1000:1)
• It has similar potencies at α1A,
α1B, and α1D subtypes
Prazosin
• Uses and Mechanism of action-
Hypertension-
Competitively blocks postsynaptic α1 adrenoceptors
resulting in vasodilatation due to unopposed β2
action in both arterioles (resistance vessels) and
vein(Capacitance vessels)
Fall in BP due to decreased peripheral resistance
• Congestive Heart Failure-
They are used in CHF as they cause dilatation of both
arteries and veins, resulting in a reduction of preload
and afterload, which increases cardiac output and
reduces pulmonary congestion.
• BPH-
There is resistance to urine outflow, due to α-
adrenergic receptor mediated increase in smooth
muscle tone in prostate neck and bladder.
α blocker relaxes smooth muscle and decrease
resistance to urine outflow
• Raynaud’s Phenomenon-
In this there is reversible digital vasospasm, often in
response to cold which blocks the flow of blood. This
causes the affected area to change colour to white,
then blue and then red, as the bloodflow returns.
α blockers causes vasodilation and helps in restoring
blood flow
• PTSD (Post Traumatic Stress Disorder)-
Since α1- adrenergic activity is associated with fear
and startle responses, Prazosin that blocks central
α1-adrenergic activity is potentially useful in PTSD.
Prazosin inhibits norepinephrine and may decrease
the arousal produced by it in response to a stressor,it
also decreases nightmares related to PTSD
• It also inhibits Phosphodiesterase which degrades
cAMP. Increase in smooth muscle cAMP contribute
to its vasodilator action.
• Pregnancy and Lactation
Pregnancy-Category ‘C’
Lactation-Excreted in breastmilk, avoid giving the
medication in lactating females
• Side effects-
Dizziness, Drowsiness, Headache, Postural
hypotension, Nausea, weakness
• The initial dose should usually be given at bedtime
so that the patient will remain recumbent for at least
several hours to reduce the risk of syncopal reactions
that may follow the first dose of prazosin known as
“first dose effect”
Selective α1-Blocker.pptx
Parameters Prazosin Terazosin Doxazosin Alfuzosin Tamsulosin Silodosin
BA 60% 90% 65% 49% 30% 32%
PPB 97% 90-94% 99% 82-90% 90% 97%
T1/2 3 hrs 12 hrs 20 hrs 3-5 hrs 5-10 hrs 13-20hrs
DOA 7-10hrs 24 hrs 36 hrs - - -
Metabolism Hepatic Hepatic Hepatic Hepatic
(CYP3A4)
Hepatic
(CYP3A4)
Hepatic
Metabolites -
6 and 7-o-
demethyl
terazosin
6 and 7-o-
demethyl
metabolite
- -
glucuronide
formed by
UGT2B7;
Excretion Urine(10%)
Rest in
feces
Feces
(55-60%),
Urine
(40%)
Feces (65%)
Rest in
urine
Feces
(69%)
Urine(24%)
Urine(76%)
Feces(21%)
Feces and
urine
equally
• Terazosin and Doxazosin -Also has Apoptosis
promoting effect on Prostate smooth muscle cells,
and retard the progression of prostatic hypertrophy
• Tamsulosin-Uroselective α1A/α1D improve BHP
symptoms, because α1A subtype predominate in the
bladder base and prostate.
• Silodosin-Silodosin exhibits selectivity for the α1A,
over the α1B.The chief side effect of silodosin is
retrograde ejaculation
THANKYOU

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Selective α1-Blocker.pptx

  • 1. Selective α1-Blocker Madhumita Dixit JR-3 Pharmacology Department Moti Lal Nehru Medical College Prayagraj, U.P.
  • 2. Prazosin Introduction- • Selective α1 blocker • Affinity for α1:α2 (1000:1) • It has similar potencies at α1A, α1B, and α1D subtypes
  • 3. Prazosin • Uses and Mechanism of action- Hypertension- Competitively blocks postsynaptic α1 adrenoceptors resulting in vasodilatation due to unopposed β2 action in both arterioles (resistance vessels) and vein(Capacitance vessels) Fall in BP due to decreased peripheral resistance
  • 4. • Congestive Heart Failure- They are used in CHF as they cause dilatation of both arteries and veins, resulting in a reduction of preload and afterload, which increases cardiac output and reduces pulmonary congestion.
  • 5. • BPH- There is resistance to urine outflow, due to α- adrenergic receptor mediated increase in smooth muscle tone in prostate neck and bladder. α blocker relaxes smooth muscle and decrease resistance to urine outflow
  • 6. • Raynaud’s Phenomenon- In this there is reversible digital vasospasm, often in response to cold which blocks the flow of blood. This causes the affected area to change colour to white, then blue and then red, as the bloodflow returns. α blockers causes vasodilation and helps in restoring blood flow
  • 7. • PTSD (Post Traumatic Stress Disorder)- Since α1- adrenergic activity is associated with fear and startle responses, Prazosin that blocks central α1-adrenergic activity is potentially useful in PTSD. Prazosin inhibits norepinephrine and may decrease the arousal produced by it in response to a stressor,it also decreases nightmares related to PTSD
  • 8. • It also inhibits Phosphodiesterase which degrades cAMP. Increase in smooth muscle cAMP contribute to its vasodilator action. • Pregnancy and Lactation Pregnancy-Category ‘C’ Lactation-Excreted in breastmilk, avoid giving the medication in lactating females • Side effects- Dizziness, Drowsiness, Headache, Postural hypotension, Nausea, weakness
  • 9. • The initial dose should usually be given at bedtime so that the patient will remain recumbent for at least several hours to reduce the risk of syncopal reactions that may follow the first dose of prazosin known as “first dose effect”
  • 11. Parameters Prazosin Terazosin Doxazosin Alfuzosin Tamsulosin Silodosin BA 60% 90% 65% 49% 30% 32% PPB 97% 90-94% 99% 82-90% 90% 97% T1/2 3 hrs 12 hrs 20 hrs 3-5 hrs 5-10 hrs 13-20hrs DOA 7-10hrs 24 hrs 36 hrs - - - Metabolism Hepatic Hepatic Hepatic Hepatic (CYP3A4) Hepatic (CYP3A4) Hepatic Metabolites - 6 and 7-o- demethyl terazosin 6 and 7-o- demethyl metabolite - - glucuronide formed by UGT2B7; Excretion Urine(10%) Rest in feces Feces (55-60%), Urine (40%) Feces (65%) Rest in urine Feces (69%) Urine(24%) Urine(76%) Feces(21%) Feces and urine equally
  • 12. • Terazosin and Doxazosin -Also has Apoptosis promoting effect on Prostate smooth muscle cells, and retard the progression of prostatic hypertrophy • Tamsulosin-Uroselective α1A/α1D improve BHP symptoms, because α1A subtype predominate in the bladder base and prostate. • Silodosin-Silodosin exhibits selectivity for the α1A, over the α1B.The chief side effect of silodosin is retrograde ejaculation