Epinephrine

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Introduction:

Epinephrine is an agonist at both A and B receptors. It is, therefore a very important vaso – constrictor and cardiac stimulant.

Epinephrine is synthesized from tyrosine in the adrenal medulla and released along small quantities of nor – epinephrine into the bloodstream.

Low doses B effects (vasodilation) predominate while on higher doses a effects (vasoconstriction) is strongest.

Mechanism:

  • Epinephrine is a sympathomimetic which are bind to adreno receptor which lies in GPCR.
  • GDP dissociates from α subunit of appropriate G protein.
  • GTP then binds to this G protein and α subunit dissociates from β – γ
  • Activated GTP – bound α subunit then regulate the activity of its effector.

Actions:

(1) Cardiovascular

  Major actions

  Epinephrine strengthens contractility of myocardium and increase its rate of contraction.

  Epinephrine activates B1 receptors on kidneys to cause renin release, an enzyme for production of angiotensin II. i.e. an important vasoconstrictor.

(2) Respiratory

–  Causes powerful Bronchodilation.

–  Also inhibits the release of allergy mediators such as Histamine from Mast cells.

(3) Hyperglycemia

–  It has significant hyperglycemic effect because of increased glycogenolysis in liver, increased release of Glucagon (B2 effect), decreased release of Insulin (a2 effect).

Clinical uses:

  • To treat Bronchospasm e.g. in acute asthma and anaphylactic shock.
  • A primary treatment of Anaphylaxis, to relieve hyper sensitivity reactions.
  • To restore cardiac activity in Cardiac Arrest.
  • To facilitate aqueous drainage in chronic open angle Glaucoma.

Adverse effects:

(1) CNS

Anxiety, Fear, Headache, Tremor

(2) CVS

Hypertension, Cardiac arrhythmias, Angina

(3) RESPIRATORY TRACT

Pulmonary edema.

Contradictions:

  • Coronary disease – may induce anginal attacks.
  • Hyperthyroidism.
  • Hypertension.
  • Chloroform, Cyclopropane, Halothane anesthesia

Dosage:

(1) IN BRONCHOSPASM

0.4ml 0f 1:1000 sol., SC

(2) IN ANAPHYLAXIS

0.3 – 0.5 mg

Properietary Names of Available Epinephrine:

  • Adecaine
  • Xylocaine
  • Xylodos

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Author: seharnaseem

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