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Pharm > Adrenergic Antagonists DSA and lecture > Flashcards

Adrenergic Antagonists DSA and lecture Flashcards

1
Q

Nonselective alpha blockers

A

phenoxybenzamine
phentolamine

They start with ph. al-PH-a blockers

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2
Q

Alpha-one selective blockers

A

prazosin

tamsulosin (alpha 1A)

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3
Q

Nonselective beta blockers

A

propanalol

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4
Q

Cardioselective beta blockers

A

cardioselective? Think Beta 1

atenolol
acebutolol
metoprolol
betaxolol

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5
Q

alpha and beta blockers

A

labetalol

carvedilol

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6
Q

Phenoxybenzamine

A

IRREVERSIBLE alpha 1 and alpha 2 blocker

noncompetitive

Mechanism. Binds covalently to alpha-1 and alpha-2 adrenergic receptors. i.e. non-selective, irreversible, alpha blocker. Onset is slow requiring 10-20 minutes for formation of covalent linkages. Offset is even slower with a t1/2 of 24 hours. Terminated by metabolism and new receptor synthesis. Called non-equilibrium or non-competitive blocker.

New receptors must be synthesized to overcome the blockade
Several (2-5) days to regenerate
“Dirty” drug - also blocks histamine, acetylcholine, & serotonin receptors

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7
Q

Phentolamine

A

prototype reversible alpha 1 and alpha 2 blocker

competitive

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8
Q

prazosin

A

selective alpha 1 A blocker

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9
Q

Tamsulosin basic action

A

selective alpha 1A blocker

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10
Q

Alpha Adrenergic Blockers in general

A

Non-selective blockers- block both alpha-one and alpha-two adrenergic receptors.

Alpha blockers are antagonists
they have no intrinsic activity but do produce pharmacological changes).

They block the effects of endogenous agonists (epinephrine; norepinephrine)

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11
Q

Phenoxybenzamine:Pharmacological Effects.

A

Vascular. Dependent on the degree of sympathetic tone. i.e., blocks the effects of endogenous NE. Reduces blood pressure. Significant side effect is Orthostatic hypotension.

  1. Cardiac. Reflex tachycardia from reducing BP, which enhances NE release. Because alpha-2 receptors on adrenergic nerves are also blocked, this further increases NE release at the heart, where it can act on beta-1 receptors.
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12
Q

Phenoxybenzamine: Other effects

A
  1. CNS. lipophilic agent which can cross the blood brain barrier. Nausea, vomiting and weakness may be signs of non-specific effects.
  2. Others: miosis, inhibition of ejaculation, stuffy nose (all alpha1 blockade).
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13
Q

Phenoxybenzamine: Clin. Uses

A

Pheochromocytoma: Pre-operative management to treat vascular effects of high circulating catecholamines. Always in combination with a beta blocker.
Peripheral Vascular Disease. Raynaud’s syndrome where sympathetic tone to peripheral vasculature is high. Acrocyanosis from frost bite.

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14
Q

Reversible Alpha Blockers

A

Competitive blockers. Rapid onset of blockade. Surmountable by high concentrations of alpha-1 agonists.

Phentolamine and Tolazoline (Imidazoline derivatives). Non-selective for alpha-1 and alpha-2 receptors. Duration of several hours. They also activate histamine receptors (adverse effect).

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15
Q

Phentolamine: Clinical Uses

A
  1. Pheochromocytoma. Acute hypertensive crisis.
  2. Clonidine withdrawal
  3. Treat necrosis due to vasoconstrictors such as NE and phenylephrine.
  4. For erectile dysfunction (ED) – has been replaced by drugs with less severe side-effects.
    Side effects: tachycardia, nausea, diarrhea, orthostatic hypotension ***.
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16
Q

Alpha-1 Selective Blockers: side effects, agents, uses

A

Block alpha-1 but not alpha-2 adrenergic receptors.
Generally reflex tachycardia is less prevalent than with non-selective alpha blockers.
Syncope is noted when first administered in a large group of patients. Caution patients to avoid sudden postural changes.
Agents: ***prazosin (Minipress), terazosin (Hytrin), doxazosin (Cardura)
Uses: Hypertension, benign prostatic hypertrophy

17
Q

Tamsulosin

A

Competitive alpha blocker; binds alpha1A with little alpha1B binding

Very limited vascular effects, but highly efficacious in benign prostatic hyperplasia (BPH).
Conclusion is that vascular effects of alpha blockers is likely an alpha1B receptor, whereas prostate alpha receptors are a1A subtype

18
Q

Yohimbine

A

a2 and 5-HT blocker
aphrodisiac, improves erectile function
Viagra has replaced its usefulness

19
Q

Ergot Alkaloids

A

Ergotamine, Ergonovine
originally found in spoiled rye (fungus), caused abortions, gangrene, convulsions
used to treat migraine (also 5-HT agonists)

20
Q

Nonselective Beta Blockers (Beta receptor antagonists)

A

Nonselective = both beta 1 and beta 2

Propranolol (prototype)
Timolol
Pindolol
- partial agonist
ISA =intrinsic sympathomimetic activity
Nadolol
21
Q

cardioselective beta blockers

A

Cardioselective = beta 1-selective

Atenolol (prototype)

Others
– Acebutolol : partial agonist, ISA

Metoprolol***
-Betaxolol

22
Q

short-acting beta blocker

and non-selective alpha and beta blockers

A

Very short acting - Esmolol

Alpha and Beta Blockers:

  • Labetolol
  • Carvedilol
23
Q

Propranolol

A

(Inderal) is the prototype beta blocker
Mechanism: Non-selective competitive antagonist at b-1 and b-2 receptors (& b-3).
High therapeutic doses may also have a non-receptor related quinidine-like or membrane-stabilizing effects.
Relatively high lipid solubility allows distribution to the CNS (some drowsiness)

24
Q

Propranolol: Pharmacological Effects on heart and blood vessels

A

The effect of antagonists is due to blocking existing tone. Effects are greater if sympathetic tone is high.

  1. Heart: decreases HR, cardiac output, and pacemaker activity.
  2. Blood vessels: Slow developing decrease in peripheral resistance. Possibly due to: central reduction in sympathetic tone and reduction in renin release (beta-1 effect)

Decreases exercise tolerance, rate of depolarization of ectopic pacemakers, decreases O2 demand, decreases AV nodal conduction (can produce AV block), decreases infarct size and re-infarction- prevent sudden death

25
Q

Propanolol: effects on bronchial smooth muscle and metabolic

A
  • Bronchial Smooth Muscle
    Block sympathomimetic bronchodilation
    *** precaution or contraindication in asthma & COPD
  • Metabolic
    Blocks beta receptor effects on lipolysis and glycogenolysis.
    *** May mask signs of hypoglycemia, e.g., tachycardia, BP changes. May potentiate insulin-induced hypoglycemia.
  • Quinidine-like effect
    “Membrane stabilizing activity”, decreased cardiac excitability
26
Q

Propanolol metabolism

A

Well absorbed following oral administration.
Up to 75% may be inactivated by first pass metabolism. There is large inter-individual variation. Variation is relatively constant for a given patient. Must titrate the dose upward for each patient.

27
Q

Beta blockers: clinical uses

A
  • Angina pectoris. Reduces cardiac work and O2 consumption.
  • Hypertension. Decreases CO and produces slow decrease in peripheral resistance due to blockade of renin release. May see Na+ and water retention with prolonged use because of reduced CO.
  • Migraine headache (Prophylactic treatment)
  • Arrhythmias: sinus tachycardia and supraventricular ectopic beat
  • Recurrent VT, VF - especially when due to ischemia
  • Pheochromocytoma
  • Thyrotoxicosis:
    hyperthyroid patients have increased receptor sensitivity
  • Adjunctive treatment for anxiety (panic) attacks (reduces peripheral sympathetic signs and symptoms, e.g., palpitations)
  • MI & Post-MI prophylaxis
    protects against arrhythmias & limits infarct size
    Acute MI: assess LV function
    5-12 days after MI, reduces O2 demand & spread of infarct zone
28
Q

Congestive Heart Failure

A

Dramatic results in recent clinical trials
Beta blockers prevent HF in more than 50%, strokes reduced by more than 38%, occurrence of CAD and other CV events significantly decreased

Mortality rate reduced 65% by carvedilol, 34% by metoprolol, 33% by bisoprolol

Beta blockers increase LVEF, cause beneficial remodeling of heart

Use only in stable CHF (class II & III), gradually titrate dose

Patients also treated with diuretic, ACE inhibitors, & digoxin

29
Q

Propranolol: Side Effects

A

Common:
dizziness, fatigue, diarrhea, constipation, nausea, depression, bizarre dreams

Severe:
purpura, rash, fever

Interferes with SGOT and BUN tests
`
Chronic use (hypertension) increases VLDL & HDL

30
Q

Beta blocker side effects

A

Use with caution in diabetics

  • inhibits compensatory response to hypoglycemia (glycogenolysis with glucose release)
  • masks signs of hypoglycemia (tachycardia) that are important “clues” to diabetic patient

Contraindicated in most asthmatics and COPD
- because block b2 bronchodilation

31
Q

beta blockers sudden withdrawal and other contraindications

A

Sudden Withdrawal: rebound hypertension, anginal attack & possibly MI if drug suddenly withdrawn after chronic therapy. Beta receptor synthesis is increased by beta blocker use. Example of receptor up-regulation.

Other Contraindications: Acute treatment of decompensated heart failure; 2nd and 3rd degree heart block, and cardiogenic shock.

32
Q

beta blocker drug interactions

A

Other hypotensive medications
–reserpine, guanethidine, methyldopa

Other anti-arrhythmic agents

  • -calcium channels blockers
  • -lidocaine

Insulin and oral hypoglycemic drugs
– prolongs hypoglycemia and masks signs

Masks symptoms of hyperthyroidism

33
Q

Other nonselective beta blockers

A

Nadolol (Corgard) - longer acting; once-per-day dosing

Timolol (Blocadren) - more potent than propranolol

Timolol (Timoptic) -

  • lowers IOP in glaucoma
  • reduces aqueous humor production

Pindolol (Visken) - partial agonist; partial blockade

  • less incidence of rebound hypertension
  • less bradycardia

Carteolol - like pindolol

34
Q

Beta-1 selective blockers

A
  • All are more potent at beta 1 than beta 2 receptors
    • at higher doses, block beta 2 as well
    • lessen risk of bronchospasm -still contraindicated in asthmatic
    • do not usually prolong hypoglycemia
  • Atenolol (Tenormin)

Acebutolol (Sectral) - partial agonist, hypertension, dysrhythmias

  • Metoprolol (Lopressor, Topral XL) – hypertension, CHF

Betaxolol (Betoptic) – glaucoma

Bisoprolol (Zebeta) - CHF

The AThENs METROPOLis BETA (beat) the spartans… they ONE (won)!

ATENolol, METROpolol Beta One

35
Q

Esmolol

A

** Very rapid onset & short duration of action
beta 1-selective
Used as IV infusion for peri-operative tachycardia and hypertension, arrhythmias
Used in electroconvulsive therapy

36
Q

Beta-Blockers with Partial Agonist Activity

A

Pindolol
Acebutolol

No demonstrated therapeutic advantage over pure antagonists. Lessened bradycardia, better lipid profile ?

ISA (Intrinsic sympathomimetic activity)

37
Q

Labetolol

A

Selective alpha 1 blocker
Nonselective beta 1 & beta 2 blocker

Clinical Uses:
hypertension
pheochromocytoma

38
Q

Carvedilol

A 
Nonselective b-blocker + a-blocker
Very lipid soluble
Also has antioxidant properties
Very dramatic results in CHF clinical trials
Decreased mortality by 65%

Pharm (14 decks)

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