Racepinephrine is an inhaled medication used to quickly open swollen airways, most commonly in children with croup and occasionally for temporary relief of mild asthma symptoms. It is a 50/50 mixture of two mirror-image forms of epinephrine (adrenaline), delivered as a mist through a nebulizer. The “race” in the name comes from “racemic,” a chemistry term meaning equal parts of both molecular forms.
How Racepinephrine Works
Epinephrine, the body’s natural adrenaline, acts on two key types of receptors. One type causes blood vessels to tighten, which shrinks swollen tissue. The other type relaxes the smooth muscle lining the airways, opening them up. Racepinephrine triggers both of these effects at once: it constricts the blood vessels in the airway walls (reducing swelling) and relaxes the airway muscles (making it easier to breathe).
Natural epinephrine in your body is almost entirely one mirror-image form, called L-epinephrine. Racepinephrine contains equal amounts of L-epinephrine and its less active counterpart, D-epinephrine. Because the D form is weaker at stimulating adrenaline receptors, racepinephrine was historically considered a gentler option, particularly for children. In practice, studies comparing the two have found that L-epinephrine alone is at least as effective as the racemic mixture, with no additional side effects. L-epinephrine is also cheaper and more widely available globally, which is why some hospitals use it interchangeably.
Primary Use: Croup in Children
Croup is an infection of the upper airway, usually caused by a virus, that makes the tissue below the vocal cords swell. It produces the distinctive barking cough and a harsh breathing sound called stridor. Racepinephrine is considered the gold-standard medication for severe croup episodes. When delivered as a nebulized mist, it reduces airway swelling rapidly, with meaningful improvement in symptoms within about 30 minutes and peak benefit around 60 minutes.
Clinical measurements show the drug can reduce standardized croup severity scores by 2 to 3 points on a common rating scale, which translates to noticeably easier breathing, less stridor, and a calmer child. The relief is real but temporary. Because the medication wears off, children treated in an emergency department are typically observed for a period afterward to make sure symptoms don’t return once the drug’s effects fade.
Over-the-Counter Availability
Racepinephrine is available without a prescription for temporary relief of mild, intermittent asthma symptoms. The main OTC brand is Asthmanefrin, sold as a 2.25% inhalation solution in single-use vials designed for a hand-held nebulizer. At that concentration, the solution delivers the equivalent of about 1% epinephrine.
The standard OTC dosing for adults and children age 4 and older is 1 to 3 inhalations from a single vial, no more often than every 3 hours, with a maximum of 12 inhalations in 24 hours. Children under 4 should not use it without a doctor’s guidance, and use by any child should be supervised by an adult. For croup and other acute settings, dosing is handled by medical professionals and may differ from what’s on the OTC label.
Side Effects and Risks
Because racepinephrine is a form of adrenaline, its side effects reflect what adrenaline does throughout the body, not just in the airways. The most important ones involve the heart and blood vessels:
- Rapid or irregular heartbeat. Adrenaline stimulates the heart, and inhaled racepinephrine can raise heart rate or trigger abnormal rhythms.
- Increased blood pressure. The same blood vessel constriction that reduces airway swelling can temporarily raise blood pressure.
- Dizziness or feeling faint. This can result from heart rhythm changes or blood pressure shifts.
- Tremor and nervousness. These are common with any form of adrenaline and usually mild.
People with heart disease, high blood pressure, or an irregular heartbeat should be cautious. These conditions can make the cardiovascular side effects more dangerous. If you notice chest pain, significant dizziness, or difficulty breathing that worsens after using racepinephrine, that warrants immediate medical attention.
Racepinephrine vs. L-Epinephrine
For years, racepinephrine was the default choice for nebulized croup treatment in the United States, partly because of a belief that the weaker D-isomer made it safer than pure L-epinephrine. A head-to-head study comparing the two in children with croup found no meaningful difference. Both produced significant, temporary reductions in croup severity scores, heart rate changes, blood pressure, and respiratory rate. Neither carried more risk than the other.
This matters practically because L-epinephrine is available everywhere in the world and costs less. Many hospitals now use either form depending on what’s in stock. If your child is treated for croup and receives L-epinephrine instead of racepinephrine, the expected outcome is the same.