This is a draft cheat sheet. It is a work in progress and is not finished yet.
Alpha agonists
-Phenylephrine- |
-Imidazolines (Naphazoline; Xylometazoline)- |
-Clonidine- |
-a-methyl dopa- |
Selective a1 agonist...VC |
Safe nasal decongestant (doesn't cross BBB) |
Acts on brain a2 receptors to cause long-phase hypotension |
Becomes a-methyl NE and acts on a2 receptors to decrease release of NE from brain. |
Used as nasal decongestant, mydriatic |
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Centrally acting antihypertensive agent |
Sympatholytic used as antihypertensive agent. |
Orally active. |
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B2 agonists
Terbutaline |
Metaproterenol |
Salbutamol/albuterol |
Salmeterol |
Formoterol |
Not metabolized by COMT or MAO |
Not metabolized by COMT |
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Resistant to COMT & MAO |
Resistant to COMT & MAO |
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Its highly lipophilic, which causes slow onset of action |
Lipophilic, but has a faster onset of action than salmeterol |
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Long-acting (t1/2=12 hrs) |
Long-acting |
All are bronchodilators used for treatment of asthma.
Long acting b2 agonist should not be given as monotherapy.
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B agonist
-Isoproterenol- |
acts on B1 & B2 receptors. |
B1: positive cardiotropic side effect |
B2: Bronchodilation |
As inhalation, injection or sublingual |
Catecholamines biosynthesis inhibitors
Metyrosine(a-methyl tyrosine) |
Reserpine "Rawlfia alk." |
Guanethidine & Guanadrel |
Inhibits tyrosine hydroxylase |
Inhibits neuronal reuptake of NE & Seretonin |
Inhibit U2 of NE |
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Passes BBB |
Don't pass BBB (due to high polarity) |
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Used for VD |
Used for VD |
Side effects: |
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1. Mental depression |
no CNS side effects |
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2. Impotence |
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3. Breast cancer |
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SAR of direct acting sympathomimetics
B-OH group: in NE & E makes the molecule chiral and thus, the (-)(R) enantiomer is the most potent due to attachment of the OH on 3 receotor binding sites instead of 2. |
Phenolic OH |
Resorcinol (such in metaproterenol) increases B2 selectivity and results in longer activity duration. |
Replacing one phenolic OH with CH2OH results in albuterol/salbutamol, which increases B2 selectivity and longer action duration. |
Removal of the para-OH, such as in phenylephrine, results in a1 agonist. |
N-atom |
Essential for alpha receptor activity. |
Bulky gp on N-atom results in decreased a-activity. |
alpha-carbon substitution |
Decreases direct receptor agonist activity, but increases a2 and B2 selectivity if a-methyl gp. |
Increases oral absorption, duration and CNS activity. |
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Beta Blockers
-Propranolol arlyoxypropanol amine - for treatment of HTN, angina and arrythmia-but it is non-cardio selective (acts on B1 & B2) |
-Timolol-treatment to glaucoma |
both may have SE broncho-constriction due to non-selectivity. |
Cardio selective BB (B1 blockers): Atenolol, Acebutolol
a1 antagonists: Quinazolines
-Prazocin- |
-Tamsulosin- |
Structure has NH2 gp on quinazoline ring responsible for a1 receptor antagonism. |
Relaxes muscles of prostate. |
Used for HTN and BPH. |
Used for BPH, chronic prostatitis, for passage of kidney stones. |
a2 antagonists are indole alkaloids.
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