Medical Pharmacology Topics   

Preliminary Outline

Alpha and Beta          Ephedrine          Pseudoephedrine Alpha Agonists   Alpha-1 and -2 Agonists          Phenylpropanolamine   Alpha-1 Agonists          Metoxiamine          Phenylephrine   Alpha-2 Agonists      Mostly CNS use          Clonidine          Guanfacine          Guanabenz      Mostly topical use          Naphazoline          Tetrahydrozoline          Oxymetazoline          Xylometazoline   Beta-1 and -2 Agonists          Isoproterenol          Metaproterenol          Terbutaline   Beta-1  Agonists          Dobutamine   Beta -2 Agonists          Albuterol          Isoetharine          Bitoterol          Ritodrine

Adrenergic Pharmacology: Agonist Drugs

Non-Selective Agonists

Ephedrine and its isomer pseudoephedrine are used as bronchodilators for their b2 activity, although they are both alpha and beta agonists. They are usually administered with an antihistamine to counter their stimulation of the CNS.

Similar chemicals that act mostly in the CNS to produce euphoria are amphetamine, methanphetamine and phentermine. These agents have no clinical application and are usually drugs of abuse.

Methylphenidate, a related drug, has mild euphopric effects and is used to treat attention deficit hyperactivity disorder (side effects include potential abuse and convulsions at high doses).

Alpha Agonists

Alpha adrenergic receptor agonists are used to treat paroxymal atrial tachycardia (PAT), nasal congestion, hypotension and eye redness. They are also used to dilate pupils and as as adjunts to local anesthetics.

Examples of alpha agonists include methoxamine (a1), phenylephrine (a1), clonidine (a2) and phenylpropanolamine (a1 and a2). Metoxiamine is the most selective for a1, and is used to treat hypotension with little side effects.

Several imidazoline-type alpha agonists are used as nasal decongestants and in eye drops: naphazoline, tetrahydrozoline, oxymetazoline, xylometazoline. Clonidine, another imidazole-type alpha agonist, is mostly an a2 agonist, but most importantly acts on the CNS to decrease SNS activity, and is used for the treatment of hypertension and as an adjunt to anesthesia. Other antihypertensive drugs similar to clonidine are guanfacine and guanabenz.

Phenylpropanolamine (PPA) is mostly an alpha agonist but still has some beta effects. It was widely used as nasal decongestant and appetite suppressant, but its abuse lead to hypertensive crisis (stroke), cardiac arythmia, myocardial infarction, seisures, and other reactions similar to amphetamine abuse. Phenylpropanolamine is sligtly less lipophilic than amphetamine, so it has similar CNS effects at higher concentrations.

Beta Agonists

Beta-adrenergic receptors are used as bronchodilators (asthma), to relax uterine muscle (premature labor) and to stimulate the heart. They are more useful for bronchodilation when inhaled because it prevents systemic COMT degradation. The most common side effects is tachycardia due to their action on b1 receptors. Examples of beta agonist include isoproterenol, metaproterenol and terbutaline. Metaproterenol is more selective to lung b2 receptors and not as suceptible to COMT degradation, so it may be taken orally.

Dobutamine is a selective b1 receptor, although it still have some action on b2 and alpha receptors. The overal result is more ionotropic than chronitropic (?). It is used to treat cardiac failure, especially acute emergencies, and for laboratory stress tests. It must be given as an IV infusion.

Several selective b2 receptors are used mostly as bronchodilators: albuterol, isoetharine and bitoterol. Ritodrine is a beta-2 agonist more selectve to uterine muscle receptors (?) and used to treat premature labor.

Continue to "Adrenergic Antagonist Drugs" or take a quiz: [Q1].

Need more practice? Answer the review questions below (after sponsor).

Questions:

1- List 6 non-selective adrenergic agonists and identify which have clinical use.

2- What are the clinical appilcations of ephedrine and pseudoephedrine.

3- What is the clinical application of methylphenidate.

4- List 6 clinical applications of a-adrenergic receptor agonists.

5- List 1 non-selective a-adrenergic receptor agonist

6- List 2 a1-adrenergic receptor agonists

7- What are the former and current clinical uses of phenylpropanolamine?

8- What is the clinical application of metoxiamine?

9- List 3 a2-adrenergic receptor agonist

10- By which other name are a2-adrenergic receptor agonists known

11- What is the main mechanism of action of clonidine?

12- What are the clinical applications of clonidine?

13- What are the symptoms of phenylpropanolamine or amphetamine abuse?

14- What are the clinical uses of b-adrenergic agonists?

15- What is the main absorption issue when using b-adrenergic agonists as bronchodilators?

16- What are the side effects when using inhaled b-adrenergic agonists as bronchodilators?

17- List 3 non-specific b-adrenergic agonists.

18- What characteristics of metaproterenol make it different from other b-adrenergic agonists?

19- List 1 selective b1-adrenergic agonist.

20- List 4 b2-adrenergic agonist.

21- What are the clinical uses of dobutamine?

22- What are the clinical uses of b2-adrenergic agonists?

23- What characteristic of ritodrine makes it different from other b2-adrenergic agonists?

Continue scrolling to answers below (after sponsor).

Hey! DON'T PEEK!!! Finish the questions fist!

Answers:

1- List 6 non-selective adrenergic agonists and identify which have clinical use.
ephedrine - clinical
pseudoepinephrine - clinical
amphetamine
methamphetamine
phentermine
methylphenidate - clinical

2- What are the clinical appilcations of ephedrine and pseudoephedrine.
Used as bronchodilators for their b2 activity.

3- What is the clinical application of methylphenidate.
Attention deficit hyperactivity disorder

4- List 6 clinical applications of a-adrenergic receptor agonists.
paroxymal atrial tachycardia
nasal congestion
hypotension
eye redness
pupil dilation
local anesthetic adjunt

5- List 1 non-selective a-adrenergic receptor agonist
Phehylpropanolamine

6- List 2 a1-adrenergic receptor agonists
metoxiamine
phenylephrine

7- What are the former and current clinical uses of phenylpropanolamine?
nasal decongestant
appetite suppresant (obsolete)

8- What is the clinical application of metoxiamine?
hypotension

9- List 3 a2-adrenergic receptor agonist
clonidine
naphazoline
tetrahydrozoline

10- By which other name are a2-adrenergic receptor agonists known
imidazole-type alpha agonists

11- What is the main mechanism of action of clonidine?
Acts on the CNS to decrease SNS activity.

12- What are the clinical applications of clonidine?
Hypertension and adjunct to anesthesia

13- What are the symptoms of phenylpropanolamine or amphetamine abuse?
hypertensive crisis, stroke
arrythmias, cardiac infarction
seisures

14- What are the clinical uses of b-adrenergic agonists?
bronchodilators, asthma
to relax utrine smooth muscle, premature labor
heart stimulation

15- What is the main absorption issue when using b-adrenergic agonists as bronchodilators?
They are most useful when inhaled because it prevents systemic COMT degradation.

16- What are the side effects when using inhaled b-adrenergic agonists as bronchodilators?
tachycardia

17- List 3 non-specific b-adrenergic agonists.
isoproterenol
metaproterenol
terbutaline

18- What characteristics of metaproterenol make it different from other b-adrenergic agonists?
It is more selective to lung b2 receptors and not as suceptible to COMT degradation, so it may be taken orally.

19- List 1 selective b1-adrenergic agonist.
dobutamine

20- List 4 b2-adrenergic agonist.
albuterol
isotharine
bitoterol
ritrodine

21- What are the clinical uses of dobutamine?
cardiac failure during acute emergencies, and laboratory tests.

22- What are the clinical uses of b2-adrenergic agonists?
bronchodilators
uterine muscle relaxation

23- What characteristic of ritodrine makes it different from other b2-adrenergic agonists?
It is more selective to uterine muscle receptors.