Asthma
Epinephrine is also used as a bronchodilator for asthma if specific β2 agonists are unavailable or ineffective.When given by the subcutaneous or intramuscular routes for asthma, an appropriate dose is 0.3 to 0.5 mg.Because of the high intrinsic efficacy (receptor binding ability) of epinephrine, high drug concentrations cause adverse side effects when treating asthma. The value of using nebulized epinephrine in acute asthma is unclear. Croup
Racemic epinephrine has historically been used for the treatment of croup. Regular epinephrine, however, works equally well. Racemic adrenaline is a 1:1 mixture of the two enantiomers of adrenaline. The L-form is the active component. Racemic adrenaline works by stimulating the alpha-adrenergic receptors in the airway, with resultant mucosal vasoconstriction and decreased subglottic edema, and by stimulating the β adrenergic receptors, with resultant relaxation of the bronchial smooth muscle. Bronchiolitis
There is a lack of consensus as to whether inhaled nebulized epinephrine is beneficial in the treatment of bronchiolitis, with most guidelines recommending against its use. Local anesthetics
When epinephrine is mixed with local anesthetics, such as bupivacaine or lidocaine, and used for local anesthesia or intrathecal injection, it prolongs the numbing effect and motor block effect of the anesthetic by up to an hour. Epinephrine is frequently combined with local anesthetic and can cause panic attacks.Epinephrine is mixed with cocaine to form Moffetts solution, used in nasal surgery. Upper airway obstruction
Upper airway obstruction with edema and stridor can be treated with racemic epinephrine. Adverse effects
Adverse reactions to adrenaline include palpitations, tachycardia, arrhythmia, anxiety, panic attack, headache, tremor, hypertension, and acute pulmonary edema.
The use of epinephrine based eye-drops, commonly used to treat glaucoma, may also lead to a buildup of adrenochrome pigments in the conjunctiva, iris, lens, and retina. Rarely, exposure to medically administered epinephrine may cause Takotsubo cardiomyopathy.Use is contraindicated in people on nonselective β-blockers because severe hypertension and even cerebral hemorrhage may result. Mechanism of action
As a hormone, epinephrine acts on nearly all body tissues. Its actions vary by tissue type and tissue expression of adrenergic receptors. For example, high epinephrine levels cause smooth muscle relaxation in the airways but cause contraction of the smooth muscle that lines most arterioles.Epinephrine acts by binding to a variety of adrenergic receptors. Epinephrine is a nonselective agonist of all adrenergic receptors, including the major subtypes α1, α2, β1, β2, and β3. Epinephrines binding to these receptors triggers several metabolic changes. Binding to α-adrenergic receptors inhibits insulin secretion by the pancreas, stimulates glycogenolysis in the liver and muscle, and stimulates glycolysis and inhibits insulin-mediated glycogenesis in muscle. β adrenergic receptor binding triggers glucagon secretion in the pancreas, increased adrenocorticotropic hormone (ACTH) secretion by the pituitary gland, and increased lipolysis by adipose tissue. Together, these effects increase blood glucose and fatty acids, providing substrates for energy production within cells throughout the body. In the heart, the coronary arteries have a predominance of β2 receptors, which cause vasodilation of the coronary arteries in the presence of epinephrine.Its actions increase peripheral resistance via α1 receptor-dependent vasoconstriction and increase cardiac output via its binding to β1 receptors.