Adrenergic Agonists & Antagonists

Epinephrine (EP)

• A prototype adrenergic drug that is a potent agonist of
all adrenergic receptors.

Epinephrine (EP)

• Used in emergency cases systemically for treating
anaphylaxis & cardiac resuscitation.

Epinephrine (EP)

• Used to prolong local anesthesia through
vasoconstriction.

Epinephrine (EP)

• Used to control localized hemorrhage.

Epinephrine (EP)

• Used to treat open-angle glaucoma.

Epinephrine (EP)

• Not administered orally.

Norepinephrine (NE)

A prototype adrenergic drug that is a potent agonist of
all receptors except β2
-receptors.

Norepinephrine (NE)

• At similar doses, it increases BP more than Epi.

Norepinephrine (NE)

• At lower doses, it causes vasodilation and low BP.

Norepinephrine (NE)

• Used in cases of severe hypotension usually
administered IV as a continuous infusion with careful
monitoring.

Norepinephrine (NE)

• Not administered orally.

Isoprenaline (IS)

a.k.a. Isoproterenol is a potent β-adrenoceptor agonist.

Isoprenaline (IS)

• Used rarely for acute bronchial constriction and
Complete Atrioventricular (A-V) Block or Sick Sinus
Syndrome.

Isoprenaline (IS)

• Used occasionally as adjunctive therapy in shock or
heart failure.

Isoprenaline (IS)

• Not administered orally.

Dopamine (DA)

Causes the release of NE from adrenergic neurons,
which activates α1
- and β1
-receptors and it has
dopaminergic effects.

Dopamine (DA)

• Used to treat cardiogenic/septic shock and acute
heart failure.

Dopamine (DA)

• Should only be used in critical care settings (ICU)
where adequate monitoring can be provided.

Dopamine (DA)

• Not administered orally.

Phenylephrine

An α1
-receptor agonist with some β-adrenergic
stimulatory properties at high doses.

Phenylephrine

• It is administered parenterally, orally, or topically.

Phenylephrine

• Preferred over Epi as a vasopressor during gas
anesthesia.

Phenylephrine

• Used as a topical (oral in humans) nasal decongestant.

Phenylephrine

• Used in ophthalmology as a mydriatic agent.

Phenylephrine

• May elicit a reflex bradycardia when administered IV.

Phenylephrine

DO NOT GIVE to geriatric, hyperthyroid, or
hypertensive patients.

Phenylephrine

• Nasal irritation and rebound congestion (rhinitis
medicamentosa) may occur following long-term nasal
use.

Phenylpropanolamine

A nonselective adrenergic drug that affects α1 and β1
receptors with mixed-acting properties.

Phenylpropanolamine

• Used primarily for urethral sphincter hypotonus in
small animals.

Phenylpropanolamine

• It has little CNS stimulatory activity.

Ephedrine

Similar properties with phenylpropanolamine but with
β-receptor activity.

Ephedrine

• A Schedule V drug used to treat asthma-like
conditions, as a mydriatic, and to treat urinary bladder
sphincter incompetence.

Dobutamine

Activates β1
-receptors, and activates weakly β2
- and α1
-
receptors as well.
•

Dobutamine

• Used mainly for short-term treatment of heart failure in
horses and other large animals.
•

Dobutamine

• Useful in shock patients when fluid therapy alone has
not restored acceptable arterial blood pressure,
cardiac output, or tissue perfusion.
•

Dobutamine

• It may induce cardiac arrhythmias and increase
myocardial oxygen demand.

Terbutaline

An orally-effective selective β2
-receptor agonist used
as a bronchodilator.
•

Terbutaline

• Bronchodilator of choice for animals with heart
disease, hyperthyroidism, or hypertension.

Terbutaline

• Not used orally in horses.

Terbutaline

• BANNED FOR USE IN LIVESTOCK (DA A.O. NO. 14, s.
2003, May 12, 2003)

Albuterol

a.k.a. Salbutamol, with same effects and uses as
terbutaline.

Albuterol

• Used principally in dogs and cats as aerosol or tablets
for its effects on bronchial smooth muscle to alleviate
bronchospasm or cough.

Albuterol

• • Used in horses as a bronchodilator.

Albuterol

BANNED FOR USE IN LIVESTOCK (DA A.O. NO. 14, s.
2003, May 12, 2003)

Clenbuterol

Similar mechanism with albuterol.
•

Clenbuterol

• Used orally in horses as a bronchodilator for airway
obstruction.

Clenbuterol

• DO NOT USE in horses with suspected cardiovascular
impairment.
•

Clenbuterol

• BANNED FOR USE IN LIVESTOCK (DA A.O. NO. 14, s.
2003, May 12, 2003)

Ractopamine

A selective β2
-adrenergic agonist that is approved as a
partitioning agent in livestock.
•

Ractopamine

• • • Used as a feed additive mainly in swine and cattle to
improved rate of weight gain, feed efficiency, and
increase carcass leanness.

Ractopamine

No pre-slaughter withdrawal time needed.

Ractopamine

Personnel protection is needed when handling
ractopamine.

Isoxsuprine

A selective β2
-adrenergic agonist, which causes
vasodilatation in skeletal muscle.
•

Isoxsuprine

• Used to treat navicular disease in horses.
•

Isoxsuprine

• At high doses, it can decrease blood viscosity and
reduce platelet aggregation

Phenoxybenzamine

Irreversibly blocks α1
-receptors resulting to long DOA.

Phenoxybenzamine

• Used in small animals primarily for its effect in reducing
internal urethral sphincter tone relieving urinary
retention.
•

Phenoxybenzamine

• Used to treat laminitis and secretory diarrhea in
horses.
•

Phenoxybenzamine

• DO NOT USE in hypotensive animals and in horses
with colic.

Phenoxybenzamine

• Not available in the Philippines.

Irreversibly blocks α1
-receptors resulting to long DOA.
• Used in small animals primarily for its effect in reducing
internal urethral sphincter tone relieving urinary
retention.
• Used to treat laminitis and secretory diarrhea in
horses.
• DO NOT USE in hypotensive animals and in horses
with colic.
• Not available in the Philippines.

Irreversibly blocks α1
-receptors resulting to long DOA.
• Used in small animals primarily for its effect in reducing
internal urethral sphincter tone relieving urinary
retention.
• Used to treat laminitis and secretory diarrhea in
horses.
• DO NOT USE in hypotensive animals and in horses
with colic.
• Not available in the Philippines.

Irreversibly blocks α1
-receptors resulting to long DOA.
• Used in small animals primarily for its effect in reducing
internal urethral sphincter tone relieving urinary
retention.
• Used to treat laminitis and secretory diarrhea in
horses.
• DO NOT USE in hypotensive animals and in horses
with colic.
• Not available in the Philippines.

Prazosin

A competitive and selective α1
-receptor antagonist.

Prazosin

• Used in the treatment of congestive heart failure and
hypertension.

Prazosin

• Used to relax the urinary sphincters and reduce
recurrence of urinary blockage in cats.
•

Prazosin

• Use in caution on patients with chronic renal failure or
preexisting hypotensive conditions.

Phentolamine

A competitive α1
- and α2
-receptor antagonist.

Phentolamine

• Used to treat hypertension resulting sympathomimetic drug overdose.

Tolazoline

Has similar properties with phentolamine.

Tolazoline

• Used to reverse the effects of alpha-2 agonist in
ruminants.

Tolazoline

• DO NOT USE in animals exhibiting signs of stress,
debilitation, cardiac disease, sympathetic blockage,
hypovolemia, or shock.

Yohimbine

A competitive α2
-receptor antagonist.
•

Yohimbine

• Used to reverse the effects of alpha-2 agonist and
amitraz in monogastric animals.
•

Yohimbine

• Adverse effects are primarily CNS stimulation,
tachycardia, hypertension, increase in GI motility, and
increase plasma insulin levels.

Atipamezole

An α2
-antagonist, which is labeled for use as a reversal
agent for medetomidine and dexmedetomidine.

Atipamezole

• NOT RECOMMENDED in pregnant or lactating
animals.

Propranolol

A nonselective β-receptor antagonist that
competitively blocks both β1
- and β2
-receptors.

Propranolol

• Used to treat cardiac arrhythmia and hypertension
associated with thyrotoxicosis and
pheochromocytoma, respectively.
•

Propranolol

• Up-regulation occurs with long-term therapy.
•

Propranolol

• DO NOT USE in animals with asthma, heart failure or
sinus bradycardia, or hepatic disease.

Atenolol

A competitive β1
-receptor antagonist.
•

Atenolol

• Used primarily for hypertension and tachyarrhythmias
in small animals.
•

Atenolol

• Relatively safe in asthmatic patients.
•

Atenolol

• Used with caution in patients with congestive heart
failure, or renal failure, or sinus node dysfunction

metoprolol

A selective β1
-receptor antagonist.

metoprolol

• Combines the therapeutic use of propranolol and
atenolol.

metoprolol

• Relatively safe in asthmatic patients.

esmolol

A selective β1
-receptor antagonist with short DOA.

esmolol

• Similar therapeutic use with propranolol.

esmolol

•
• Used occasionally for acute management of dynamic
left ventricular outflow obstruction in cats with
hypertrophic cardiomyopathy (HCM).
•

esmolol

• Undergoes rapid enzymatic hydrolysis by red blood
cell esterases.

Sotalol

A nonselective β-receptor antagonist which can
prolong the duration of action potential and
refractory period in the heart.

Sotalol

• Does not have any appreciable first-pass effect.

Sotalol

• Does not have any appreciable first-pass effect.