# Levosalbutamol

Levosalbutamol, also known as levalbuterol, is a β$_2$-adrenergic receptor agonist used in the treatment of bronchospasm. Levosalbutamol is the (R)-(−)-enantiomer of its prototype drug salbutamol.

## Medical use

Levosalbutamol is indicated for the treatment or prevention of bronchospasm in people aged four years of age and older with reversible obstructive airway disease.

### Comparison to salbutamol

Evidence is inconclusive regarding the efficacy of levosalbutamol versus salbutamol (albuterol) or salbutamol-levosalbutamol combinations, though levosalbutamol is believed to have a better safety profile due to its more selective binding to β$_2$ receptors (primarily in the lungs) versus β$_1$ (primarily in heart muscle).
A 2013 systematic review of the use of levalbuterol as a treatment for acute asthma found that it "was not superior to albuterol regarding efficacy and safety in subjects with acute asthma." The review concluded: "We suggest that levalbuterol should not be used over albuterol for acute asthma."

## Adverse effects

Generally, levosalbutamol is well tolerated. Common mild side effects include an elevated heart rate, muscle cramps, and gastric upset (including heartburn and diarrhea).
Symptoms of overdose in particular include: collapse into a seizure; chest pain (possible precursor of a heart attack); fast, pounding heartbeat, which may cause raised blood pressure (hypertension); irregular heartbeat (cardiac arrhythmia), which may cause paradoxical lowered blood pressure (hypotension); nervousness and tremor; headache; dizziness and nausea/vomiting; weakness or exhaustion (medical fatigue); dry mouth; and insomnia.
Rarer side effects may indicate a dangerous allergic reaction. These include: paradoxical bronchospasm (shortness of breath and difficulty breathing); skin itching, rash, or hives (urticaria); swelling (angioedema) of any part of the face or throat (which can lead to voice hoarseness), or swelling of the extremities.

## Pharmacology
### Mechanism of action

Activation of β$_2$ adrenergic receptors on airway smooth muscle leads to the activation of adenylate cyclase and to an increase in the intracellular concentration of 3',5'-cyclic adenosine monophosphate (cyclic AMP). The increase in cyclic AMP is associated with the activation of protein kinase A, which in turn, inhibits the phosphorylation of myosin and lowers intracellular ionic calcium concentrations, resulting in muscle relaxation.
Levosalbutamol relaxes the smooth muscles of all airways, from the trachea to the terminal bronchioles. Increased cyclic AMP concentrations are also associated with the inhibition of the release of mediators from mast cells in the airways. Levosalbutamol acts as a functional agonist that relaxes the airway irrespective of the spasmogen involved, thereby protecting against all bronchoconstrictor challenges.
While it is recognized that β$_2$ adrenergic receptors are the predominant receptors on bronchial smooth muscle, data indicate that there are beta receptors in the human heart, 10–50% of which are β$_2$ adrenergic receptors. The precise function of these receptors has not been established. However, all β adrenergic agonist drugs can produce a significant cardiovascular effect in some patients, as measured by pulse rate, blood pressure, and restlessness symptoms, and/or electrocardiographic (ECG).

## Society and culture

Levosalbutamol is on the list of drugs banned by the World Anti-Doping Agency.

### Economics

Levalbuterol is more costly than salbutamol.

### Legal status

Levalbuterol was approved in the United States as a solution to be used with a nebulizer device in March 1999, and in March 2005, became available in a formulation with a metered-dose inhaler under the brand name Xopenex HFA (levalbuterol tartrate inhalation aerosol).

### Names

Levosalbutamol is the international nonproprietary name and levalbuterol is the United States Adopted Name.