Beta2 sympathomimetics

Beta2 sympathomimetics or beta2 receptor agonists belong to the group of bronchodilators. Their name is derived from their ability to activate the beta2-receptors. These are involved in the transmission of stimuli in a part of the sympathetic nervous system.

Examples of short-acting beta-2-symptathomimetic drugs (SABA):

• Fenoterol
• Salbutamol
• Terbutaline

Examples of long-acting beta2 sympathomimetics (LABA) for inhalation:

• Formoterol
• Salmeterol
• Indacaterol (see above)

LABA for oral administration:

• Bambuterol
• Clenbuterol

Numerous combination preparations of long-acting beta2 sympathomimetics and inhaled glucocorticoids are available.

A basic distinction is made between the

• long-acting beta2-sympathomimetics: long-acting beta-2-sympathomimetics = Long acting beta2-agonist- LABA, for long-term therapy or prevention of seizures. The effect lasts for about 12 to 24 hours. The substances are often used in combination with an inhaled glucocorticoid, since beta-2 sympathomimetics themselves have no anti-inflammatory activity.

and the

• short-acting beta-2 sympathomimetics: = Short acting beta2-agonist -SABA /= rapid-acting beta-2 agonists-RABA (rapid-acting beta-2 sympathomimetics), with rapid onset of action for the treatment of acute symptoms. The effect sets in within a few minutes and lasts for about three to six hours.

This type of drug, known as uLABA (ultra Long Acting Beta 2 Agonists), is available with a further extended duration of action and only requires a single daily dose (e.g. indacaterol) (Beier J 2009).

The fast-acting substances (such as salbutamol, fenoterol and reproterol) are mainly used as so-called "relievers" in the acute therapy of obstructive respiratory diseases, whereas the long-acting substances (salmeterol and formoterol) are used as "controllers" in long-term therapy.

Beta-2 sympathomimetics are mainly used as topical agents (beta-2 sympathomimetics are mostly inhaled as a metered dose aerosol, spray or solution via inhalers) in bronchial asthma and obstructive pulmonary diseases (salbutamol, terbutaline, formoterol, salmeterol). They activate the_{β2 receptors} of the smooth bronchial muscles. Some substances are also used as oral forms of application (bambuterol, clenbuterol). They lead via bronchospasmolysis to a reduction in airway resistance. This effect is mainly due to the opening of the Ca++ -activated Kv-channels which are placed in the plasma membrane of the muscle cells. The opening of these channels leads to a hyperpolarization of the plasma membrane and thus to a reduced influx of Ca++ ions via voltage-dependent Ca++ channels. This leads to relaxation of the smooth muscle cell.

Apart from this effect on bronchial muscle tone, beta2 sympathomimetics activate the mucociliary clearing function. They also inhibit the release of inflammatory mediators from mast cells and other inflammatory cells.

Typical side effects occur mainly with systemic use. These include an increase in heart rate, palpitations, headaches, tremors, restlessness, nausea and muscle cramps (see also under the individual drugs).

The β2 receptor-induced activation of the Na+/K+-ATPase in muscle cells leads to the development of passagere hypokalemias.

The activation of β2 receptors on hepatocytes can lead to increased hepatic glucose production and to an increase in blood sugar.

The cause of the skeletal muscle hypertrophy observed mainly with systemic application is unclear (Cave: use of beta2 sympathomimetics as doping agent = clenbuterol doping, is also used in calf fattening!) Especially in endurance sports clenbuterol acts as a performance enhancing drug.

Allergic reactions, anaphylactic shock

Hypersensitivity to the active substance, severe hyperthyroidism, hypertrophic obstructive cardiomyopathy.

1. Beier J (2009) Bronchodilator effects of indacaterol and formoterol in patients with COPD, Pulm Pharmacol Ther 22:492-496.
2. Buhl, R., et al.: S2k guideline for diagnosis and therapy of patients with asthma. In: Pneumology 2017; 71: 849-919
3. Graefe KH et al. Obstructive respiratory diseases. In: Graefe KH et al (Eds) Pharmacology and Toxicology. Georg Thieme Publisher Stuttgart S.533
4. Pfaar, O. et al.(2014) S2k guideline for (allergen-) specific immunotherapy for IgE-mediated allergic diseases. Allergo J Int 23: 282
5. Ring, J. et al.(2014) S2k guideline on acute therapy and management of anaphylaxis. Allergo J Int 23: 96-112.

Major drug interactions of β2-sympathomimetic drugs