Pharmacology
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Adrenergic Drugs Lec.4
Adrenergic Antagonists
Adrenergic antagonists can be divided into two types
depending on the type of the receptors that are blocked:
1. Alpha adrenergic antagonists.
2. Beta adrenergic antagonists.
Alpha Adrenergic antagonists
Classification:
Reversible: Phentolamine, tolazoline, prazosin.
Irreversible: Phenoxybenzamine.
Selective
α1 receptor blockade: prazosin, terazosin,
doxazosin.
Non-selective(
α1andα2): Phentolamine, tolazoline,
phenoxybenzamine.
Therapeutic uses of alpha blockade
1. Essential hypertension
2. Reversal of toxicity from alpha 1 agonists
3. Benign prostatic hyperplasia
4. Pheochromocytoma.
5. Raynaud's disease
Adverse effects of alpha adrenergic blocking agents:
1. Orthostatic hypotension
2. Reflex tachycardia
3. Nasal congestion
4. Inhibition of ejaculation
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Pharmacology
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Beta Adrenergic Antagonists
Classification:
Pure antagonists: Atenolol, metoprolol, propranolol, nadolol.
Partial agonists: penbutolol, pindolol, acebutolol.
Membrane stabilising effect: acebutolol, metoprolol, propranolol (local anaesthetic effect).
β1 Selectivity: acebutolol, atenolol, metoprolol.
Non selectives: nadolol, propranolol, penbutolol, pindolol, timolol (
β1 and β2).
Therapeutic uses of Beta blockade:
1.Angina pectoris
2.Hypertension
3.Cardiac dysrhythmias
4.Myocardial infarction
5.Hyperthyroidism
6. Migraine
7.Pheochromocytoma
8. Glaucoma
Adverse effects of beta blockade:
1.Bronchoconstriction.
2.Heart block.
3.Decrease peripheral blood flow causing cold extremities.
4.Decrease blood flow to the liver and kidneys
5.Increase lipids Concentration
6.Mask hypoglycemic symptoms.
7.CNS.
8.Allergy: skin rash, fever.
9.Impotence (sexual dysfunction).
Pharmacology
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Contraindications:
1. Asthma.
2. Chronic obstructive pulmonary disease.
3. Peripheral vascular diseases (vasospasm).
4. Combination with Ca channel blockers, particularly verapamil.
5. IDDM patients.
6. Heart failure and bradycardia.
7. Psychiatric disorders.
Questions & Answers
Q1.
α1-Receptors are associated with which one of the following effects?
(A) Cardioacceleration
(B) Vasodilation
(C) Pupillary dilation
(D) Bronchodilation
(E) Pupillary constriction
Ans.1.
The answer is C. Sympathetic stimulation causes the α1- receptors in the iris to contract, causing
pupillary dilation (mydriasis). An incre
ased heart rate is associated with β1-receptors. Vasodilation and
bronchodilation are associated with β2-receptors. Miosis (i.e., constriction of the pupils) is associated with
stimulation of muscarinic cholinergic receptors
Q2.
Which of the following adrenergic agonists at clinical doses produces dilation of
vessels in muscle, constriction of cutaneous vessels, and positive inotropic and
chronotropic effects on the heart?
(A) Phenylpropanolamine
(B) Isoproterenol
(C) Isoxsuprine
(D) Epinephrine
(E) Dobutamine
ANS.2.
The answer is D. Activation of β2-receptors, α1-receptors, and β1-receptors produces vasodilation
in muscle, constriction of skin vasculature, and positive inotropic and chronotropic effects on the heart,
respectively. The
only drug listed that activates α1-, β1-, and β2-receptors at clinical doses is epinephrine.
Phenylpropanolamine activates predominantly α1-receptors. Isoproterenol activates both β1- and β2-
receptors but not α1-receptors. Isoxsuprine is a selective β2-agonist, whereas dobutamine is a selective
β1-agonist.
Pharmacology
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Q3.
Which of the following drugs produces pupillary dilation (mydriasis) without causing
cycloplegia?
(A) Scopolamine
(B) Pilocarpine
(C) Isoproterenol
(D) Tropicamide
(E) Phenylephrine
Ans.3.
The answer is E. Phenylephrine, an α1-agonist, constricts the radial muscles of the iris to induce
mydriasis. Scopolamine and tropicamide are muscarinic antagonists that produce mydriasis and
cycloplegia. Pilocarpine is a muscarinic agonist that produces miosis when placed in the eye. Activation
of β-receptors in the eye, such as that caused by isoproterenol, does not change pupil size
Q4.
Which of the following bronchodilators is considered the safest for use in patients
with cardiac disease?
(A) Isoproterenol
(B) Terbutaline
(C) Ephedrine
(D) Epinephrine
(E) Norepinephrine
ANS.4.
The answer is B. Terbutaline would be the drug of choice when it is necessary to induce
bronchodilation in patient with heart disease. A drug with β2-agonistic activity is necessary to produce
bronchodilation. Although isoproterenol and epinephrine are β2-agonists, they are also strong β1-
agonists and thus would be expected to excite the heart. Norepinephrine has no β2-agonists effect .
Ephedrine increases the release of norepinephrine from the sympathetic nerve terminal, and also
activates both α- and β-adrenergic receptors. Although terbutaline is the drug of choice in this situation,
caution is warranted because at high doses, terbutaline may stimu
late β1- receptors as well.
Q5.
Which of the following adrenergic receptors
subtype mediates the
phenylpropanolamine-induced contraction of the trigone and sphincter muscle of the
urinary bladder? This effect is useful to treat urinary incontinence.
(A) α1 (B) α2 (C) β1 (D) β2 (E) β3
ANS.5.
The answer is A. The α1-receptors are found in sphincter muscles (except iris sphincter muscle).
Activation of α1-receptors evokes contractions of the trigone and sphincter muscle of the urinary bladder,
and thus α1-agonists can be used to control urinary incontinence.
Pharmacology
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Q6.
Metoprolol is used in a patient with hyperthyroidism showing cardiac arrhythmia. The
use of metoprolol in this patient will most likely cause
(A) hypersalivation.
(B) mydriasis.
(C) bronchoconstriction.
(D) hyperglycemia.
(E) decreased renin secretion.
ANS.6.
The answer is E. β1-Receptors mediate renin secretion, and thus blockade of these receptors will
decrease the secretion. Hypersalivation, mydriasis, bronchoconstriction, and hyperglycemia cannot be
induced by β1-blockad
Q7.
Which of the following would be most likely to increase airway resistance in a patient
with pulmonary obstruction?
(A) Albuterol
(B) Atenolol
(C) Isoproterenol
(D) Phenoxybenzamine
(E) Propranolol
ANS.7.
The answer is E. Since β2-receptors mediate bronchodilation, the blockade of these receptors will
increase airway resistance, which is detrimental to the patient with pulmonary obstruction. Propranolol
can block β2-receptors, and thus should not be used in these patients. Albuterol and isoproterenol can
activate β2-receptors to induce bronchodilation. Atenolol is a selective β1-blocker and should not block
β2-receptors at the clinical doses. Phenoxybenzamine is an α-blocker, and it does not cause
bronchoconstriction.