Levosalbutamol

Levosalbutamol, also known as levalbuterol, is a β₂-adrenergic receptor agonist used in the treatment of bronchospasm. Levosalbutamol is the (R)-(−)-enantiomer of its prototype drug salbutamol.

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

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 β₂ receptors (primarily in the lungs) versus β₁ (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."

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.

Activation of β₂ 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.