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Pharm: Pre Midterm 1 > Adrenergic Antagonists > Flashcards

Adrenergic Antagonists Flashcards

1
Q

This set of cards will discuss the adrenergic antagonists, what is the action of these drugs?

A

Bind to adrenoreceptors but do not trigger receptor mediated intracellular effects
–act by either reversibly or irreversibly binding to the receptor, thus preventing its activation by endogenous catecholamines

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2
Q

The first drugs are the alpha adrenergic blockers, what is the action of these drugs?

A

Affect blood pressure

–reduces the sympathetic tone of the blood vessels , resulting in decreased peripheral vascular resistance

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3
Q

First are the non selective alpha adrenergic blockers, phenoxybenzamine, what is the action of this drug?

A

Alkylates and thus irreversibly blocks alpha adrenergic receptors

  • -also blocks H1, muscarinic and serotonin receptors
  • -inhibits reuptake of norepinephrine by presynaptic adrenergic nerve terminals
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4
Q

What are the cardiovascular effects of phenoxybenzamine?

A

By blocking alpha receptors, phenoxybenzamine prevents vasoconstriction of peripheral vessels by endogenous catecholamines

  • -this provokes reflex tachycardia
  • -blocking alpha 2 receptors in the heart leads to increased cardiac output
  • -not used for maintaining blood pressure in hypertension
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5
Q

What is the main use of phenoxybenzamine?

A

Management of Pheochromocytoma (a catecholamine secreting tumor of cells derived from the adrenal medulla)

  • -administered in the preoperative period to help control hypertension and sweating
  • -useful in the chronic treatment of inoperable or metastatic pheo
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6
Q

A beta blocker may be required after alpha receptor blocker has been instituted why?

A

In order to control tachycardia

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7
Q

Why should a beta blocker not be given before establishing effective alpha blockage?

A

Unopposed beta blockage could cause blood pressure elevation due to increased vasoconstriction

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8
Q

What are the adverse effects of phenoxybenzamine?

A

Postural hypotension, nasal stiffness, n/v
It can inhibit ejaculation
May induce tachycardia, mediated by baroreceptor reflex, and its contraindicated in patients with decreased coronary perfusion

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9
Q

The next non selective alpha adrenergic blocker is phentolamine, what are some features?

A
  • -reversibly blocks alpha 1 and alpha 2 receptors
  • causes postural hypotension
  • -contraindicated in patients with decreased coronary perfusion
  • can trigger arrhythmias and anginal pain
  • blocks serotonin receptors, and is an agonist at muscarinic H1 and H2 receptors
  • -induces reflex cardiac stimulation and tachycardia are mediated by the baroreceptor reflex
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10
Q

What are the uses of phentolamine?

A
  1. Prevention/Control of HTN episodes that may occur as a result of stress or manipulation during preoperative preparation and surgical excision (in pheo)
  2. dx of pheochromocytoma by the phentolamine blocking test
  3. prevention of dermal necrosis after the inadvertent extravasation of norepinephrine
  4. use in HTN crisis associated with stimulant drug overdose
  5. Used in adjunct for cocaine induced acute coronary syndrome to reverse coronary artery vasoconstriction
  6. used in HTN crisis associated with withdrawal of sympatholytic antihypertensive meds (Clonidine)
  7. used in HTN crisis resulting from interaction between monoamine oxidase inhibitors and tyramine or other sympathomimetic amines
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11
Q

All alpha adrenergic blockers reverse the alpha agonist of epinephrine. Give an example of this

A

Vasoconstrictive action of epinephrine is blocked

  • -but vasodilation of other vascular beds caused by stimulation of beta receptors is not blocked
  • -therefore the systemic blood pressure decreases in response to epinephrine given in the presence of phenoxybenzamine
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12
Q

Are the actions of norepinephrine reversed when giving a patient an alpha adrenergic blocker?

A

Not reversed but diminished

–since norepinephrine lacks significant beta agonist action on the vasculature

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13
Q

The next set of drugs to discuss are the alpha 1 selective adrenergic blockers, in general what is their role?

A

Tx of hypertension

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14
Q

The prototype for alpha 1 selective adrenergic blockers is prazosin, what is the use of this drug?

A
  • -decrease peripheral vascular resistance and lowers arterial blood pressure by causing relaxation of both arterial and venous smooth muscle
  • -tachycardia reflex does not typically occur
  • -also acts on the CNS to suppress sympathetic outflow
  • -decrease LDL and TAGs, while increasing HDL
  • -approved for HTN
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15
Q

The next two drugs are alpha1 selective adrenergic blockers, Terazosin and Doxazosin, what is their use?

A

longer half life than prazosin, allowing less frequent dosing
–approved for HTN and BPH

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16
Q

The last alpha1 selective adrenergic blocker is tamsulosin what is the use of this drug?

A

Alpha 1 adrenoceptors mediate contraction of GI as well as vascular smooth muscle
–therefore they treat BPH

17
Q

There are three subtypes of alpha receptors: alpha 1a, alpha1b and alpha1d. which subtype does tamsulosin fall under?

A

Selective antagonist at alpha 1a receptors

  • -alpha1a predominates in GI smooth muscle
  • -selectivity for this receptor decreases the incidence of orthostatic hypotension
  • -very little effect on blood pressure
18
Q

Therefore alpha 1 selective adrenergic blockers are used for HTN and BPH. explain the effects on HTN

A
  • -Prazosin and congeners are used in tx of HTN
  • -they are not drugs of choice for HTN
  • -the first dose produces an exaggerated hypotensive response that can result in syncope – called the first dose effect
19
Q

Explain the effects on BPH for alpha 1 selective adrenergic blockers

A

Alpha1 receptors in the trigone muscle of the bladder and urethra contribute to resistance to outflow of urine

  • -alpha1 adrenergic antagonists relax smooth muscle in the bladder neck, prostate capsule and prostatic urethra improving urinary flow
  • -alpha 1 adrenergic blockers are the drug of choice for BPH
20
Q

What are the adverse effects of alpha one blockers?

A

May cause dizziness, lack of energy, nasal congestion, headache, drowsiness, orthostatic hypotension

  • –retain sodium and fluid so frequently are given with a diuretic
  • –male sexual function is not as severely affected by these drugs as it is by phenoxybenzamine or phentolamine
21
Q

Lastly in regards to alpha blockers is the alpha 2 selective adrenergic blocker, yohimbine, what is the use?

A
  • -Tx erectile dysfunction but phosphodiesterase type 5 inhibitors have replaced it
  • -can reverse the antihypertensive effects of an alpha 2 adrenoreceptor agonist such as clonidine
22
Q

Next we will discuss beta adrenergic blockers, why are these drugs clinically important?

A

–Efficacy in the treatment of HTN, ischemic heart disease, CHF and arrhythmias

23
Q

Beta adrenergic blockers are classified on the basis of receptor subtype selectivity and partial agonist activity:

A
  1. Non selective beta blockers: block both beta1 and beta2
  2. Cardioselective beta blockers: primarily block B1
  3. alpha 1 and beta blockers
  4. partial agonists
24
Q

The first non-selective beta adrenergic antagonist is propranolol, which blocks beta 1 and beta 2, what are the cardiovascular effects?

A

–Slows heart rate and decreases myocardial contractility
when sympathetic nervous system is activated, during exercise or stress, beta blockers attenuate (Reduce) the expected rise on heart rate
–Short term administration of beta blockers decreases cardiac output
–peripheral resistance increases due to blockage of vascular beta2 receptors and compensatory sympathetic reflexes activate vascular alpha adrenergic receptors

25
Q

When propranolol is given patients with HTN show a gradual reduction of both systolic and diastolic pressure what is the mechanism for this?

A
  1. Reduction in cardiac output
  2. Reduction of renin release from the JG cells
  3. Central action, reducing sympathetic activity
26
Q

Why do beta blockers not induce postural hypotension?

A

–because alpha1 adrenoreceptors remain unblocked, therefore, normal sympathetic control of the vasculature is maintained

27
Q

What are the respiratory effects of propranolol?

A
  • -Contraction of the bronchiolar smooth muscle which can precipitate a respiratory crisis in patients with COPD or asthma
  • -do not give in a patient with asthma
28
Q

What are the metabolic effects of propranolol?

A

leads to decreased glycogenolysis and decreased glucagon secretion.
–therefore is an insulin dependent diabetic is given this drug pronounced hypoglycemia may occur after insulin injection

29
Q

What are the uses for beta blockers?

A
  1. HTN:decrease cardiac output
  2. Glaucoma: diminish intraocular pressure in glaucoma by decreasing secretion of aqueous humor by the ciliary body
  3. Migraine: prophylaxis of migraine
  4. Hyperthyroidism: blunting sympathetic stimulation that occurs in hyperthyroidism
  5. Angina: decrease the O2 requirement of heart muscle therefore are effective in reducing chest pain on exertion. (Contraindicated in variant angina)
  6. Atrial Fibrillation: control ventricular rate in patients with a-fib and in rapid ventricular response
  7. MI: beta blockers have a protective effect on the myocardium. therefore protecting patients from a second MI. Immediately after MI beta blockers reduce infarct size and hastens recovery.
  8. Performance anxiety (stage fright):use propranolol and other beta blockers
  9. Essential tremor
30
Q

One of the adverse effects of beta blockers is brochoconstriction, explain

A

Lethal adverse effects in asthmatics

31
Q

Another adverse effects of beta blockers is metabolic and endocrine effects, explain

A
  • -Catecholamines promote glycogenolysis and mobilize glucose in response to hypoglycemia
  • -non selective beta blocks may adversely affect recovery from hypoglycemia in insulin dependent diabetics.
  • -all beta blockers mask tachycardia that is seen in hypoglycemia.
32
Q

Explain the effects of beta blockers on lipase

A
  • -beta receptors mediate activation of hormone sensitive lipase in fat cells leading to release of free fatty acids into the circulation — non selective beta antagonists can attenuate the release of free fatty acids from the adipose tissue
  • —non selective beta antagonists reduce HDL, increase LDL, and increase triglycerides
  • -B1 antagonists improve the serum lipid profile of dyslipidemic patients
33
Q

What are the CNS effects of beta blockers?

A

Sedation, dizziness, lethargy, fatigue, depression

–lower liposolubility = lower incidence of CNS adverse effects

34
Q

What are warnings or precautions for beta blockers?

A
  1. Therapy should not be withdrawn abruptly but tapered to avoid tachycardia, hypertension and or ischemia.
35
Q

What is the drug Nadolol used for?

A

Nonselective beta blocker

  • -long duration of action
  • -indicated for long term management of patients with angina
  • -indicated for management of HTN
36
Q

What is the drug Timolol used for?

A

Nonselective beta blocker

  • -tx of hypertension
  • -prophylaxis of migraine headache
  • -treatment of open angel glaucoma

Pharm: Pre Midterm 1 (30 decks)

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