|Systematic (IUPAC) name|
|Pregnancy cat.||A (AU) C (US)|
|Legal status||Prescription Only (S4) (AU) POM (UK) ℞-only (US)|
|Routes||IV, IM, endotracheal, IC|
|Metabolism||adrenergic synapse (MAO and COMT)|
Racemic epinephrine is a racemic mixture of epinephrine and is a sympathomimetic bronchodilator that is delivered by aerosol. Commonly used in croup (laryngotracheobronchitis) and when stridor is present after removal of an endotracheal tube (extubation). Racemic epinephrine prepared for aerosolization is equivalent to a 1:100 dose of epinephrine.
The term racemic epinephrine refers to a mixture of 50 % each of the dextro-rotatory and levo-rotatory isomers. The l-isomer [(R)-epinephrine] is present in the adrenal glands of animals and humans and is produced commercially by extraction from animal glands or by separation of the d- and l-isomers in the synthetic preparation. It is the epinephrine listed in the US Pharmacopoeia. The important difference in these isomers is in their physiological properties. The d-isomer [(S)-epinephrine] has about one fifteenth the pressor effect of the l-isomer, but has a more sustained action. Together the two isomers give a more prolonged result than the l-form—epinephrine USP—alone. The racemic form has also been shown to be more stable under varying conditions of storage. Studies have further demonstrated the racemic form gives better protection as an antihistaminic.
Racemic epinephrine may be indicated when there is stridor present or when croup is suspected. Nebulized and inhaled epinephrine (both racemic and levo(1)-epinephrine) has been shown to decrease hospitalization rates in cases of bronchiolitis. Inhaled epinephrine is also recommended as a first-line treatment for bronchiolitis usually in conjunction with inhaled hypertonic saline and dexamethasone.
Side effects include increased heart rate, nausea, anxiety, heart palpitations and headache.
Mechanism of action
Racemic epinephrine works by stimulation of the α-adrenergic receptors in the airway with resultant tightening of the mucosa (mucosal vasoconstriction) and decreased fluid in the airway (subglottic edema) and by stimulation of the β-adrenergic receptors causing relaxation of the bronchial smooth muscle.
Racemic epinephrine prepared for aerosolization is equivalent to a 1:100.
- Adults: 0.5–0.75 ml of a 2.25% solution in 2.0 ml normal saline.
- Pediatrics: 0.25–0.75 ml of a 2.25% solution in 2.0 ml normal saline.
Common brand names include:
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