Treating Asthma With Xopenex

a doctor helps a young patient use an inhaler

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Xopenex (levalbuterol) is an inhaled medication for the treatment of acute asthma symptoms, including coughing, wheezing, shortness of breath and chest tightness. Xopenex works by relaxing the smooth muscles around the lungs, usually within a few minutes of taking the medication. Xopenex is available both as an inhaler as well as in a solution form delivered via a nebulizer machine.

Xopenex is the active isomer of albuterol (called R-albuterol or levalbuterol). The chemical structures of medications exist as a mixture of mirror images of one another (referred to as a racemic mixture), and only one of these forms is the active medication.

The inactive form (called S-albuterol or dextroalbuterol) serves no purpose except that it “gets in the way” of the active form and may still contribute to side effects. This was the purpose of why Xopenex was developed—to improve the function of albuterol while decreasing the side effects.

Xopenex vs. Albuterol

It’s not completely clear. When Xopenex was first developed, animal studies suggested that S-albuterol caused inflammation in the lungs, which could possibly worsen asthma. It was also thought that as more racemic albuterol ( a mixture of the R and S-albuterol isomers) was taken, the S-albuterol isomer would accumulate within the lungs and result in contraction of the smooth muscles around the lungs, thereby worsening asthma symptoms.

Xopenex was therefore expected to work better at treating asthma symptoms than racemic albuterol. Early studies did show that Xopenex was better at treating asthma than albuterol since less Xopenex was needed to achieve control of asthma symptoms than comparable amounts of albuterol.

Since Xopenex is the active half of albuterol, one would expect that half the dose of Xopenex would be equivalent to twice the dose of albuterol; however, these studies suggested that only one-fourth of the dose of albuterol as needed to achieve the same result when using Xopenex.

This was thought to be due to the lack of the S-albuterol isomer in Xopenex, which was working against the R-albuterol isomer. Recent data on Xopenex, however, along with an overview of all of the available data, suggests that Xopenex is no better at treating asthma than would be expected.

The dose of Xopenex required to achieve the same result of treating asthma does appear to be approximately one-half, which is what is expected since it contains the active isomer (R-albuterol). The S-albuterol isomer appears to be inert, meaning that it does not act for or against the treatment of asthma symptoms.

Xopenex and Albuterol Side Effects

Albuterol is well-known to cause certain side effects, including muscle tremors, jitteriness, palpitations, and increased heart rate. Early studies on Xopenex suggested that because far less medicine was needed to achieve the same benefit as albuterol, fewer side effects would occur.

In addition, it was initially thought that the S-albuterol isomer was primarily responsible for many of the albuterol side effects, and therefore Xopenex, which does not contain the S-albuterol isomer, would cause few side effects.

Recent studies suggest, however, that the side effects of Xopenex are equivalent to albuterol since it is actually the R-albuterol isomer that is responsible for the albuterol side effects.

The S-albuterol isomer is inert, meaning it does not contribute to side effects. The package insert for Xopenex states that the rate of the above-mentioned side effects is similar for equivalent doses of Xopenex and albuterol.

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Article Sources

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