Mechanism of action and pharmacodynamics
Like other members of the group (salbutamol, fenoterol, formoterol), salmeterol selectively stimulates $\beta_2$-adrenergic receptors. This leads to high bronchodilator efficacy through the relaxation of the bronchial smooth muscle.
In addition to its direct bronchodilator effect, the drug possesses important additional effects:
- Mast cell stabilization: prevents their degranulation, thereby inhibiting the release of inflammatory and allergic mediators into the lumen of the respiratory tract.
- Improvement of drainage function: facilitates sputum clearance by increasing mucociliary clearance.
Pharmacokinetics: Place Among Analogues
The key feature of salmeterol lies in its pharmacokinetics upon inhalation administration. Unlike other $\beta_2$-adrenergic agonists, it has a delayed onset of action.
Comparative characteristics:
- Short-acting drugs (3–6 hours) (e.g., salbutamol, fenoterol): the latent period is only 1–3 minutes, with the peak effect occurring in 30–60 minutes.
- Long-acting drugs (12 hours):
- Formoterol: acts rapidly (onset in 1–3 min), peaking at 2 hours.
- Salmeterol: latent period of 15–30 minutes, with the maximum effect developing only after 2–4 hours.
Clinical application
Due to the slow onset of the effect, salmeterol is strictly unsuitable for relieving acute bronchospasm attacks (short-acting $\beta_2$-adrenergic agonists are the drugs of choice for these purposes). Its niche is maintenance therapy and prevention.
Combination therapy in COPD: In clinical practice, it is rational to combine $\beta_2$-adrenergic agonists with anticholinergics (M-anticholinergics) (e.g., ipratropium bromide or tiotropium bromide). The goals of such a combination are:
- Achieving synergy (mutual enhancement of the bronchodilator effect).
- Reduction of the $\beta_2$-adrenergic agonist dose, which helps minimize its systemic side effects.
Prescription writing rules
The drug is available as a metered-dose inhalation aerosol.
Prescription example: Rp.: Aerosoli Salmeteroli 0.000025 g D.t.d. N. 1 S. 1 inhalation (25 mcg) 2 times a day.
"Salmeterol is the slowest": unlike salbutamol and formoterol, its effect takes 15–30 minutes to appear, which is why it is used for prevention rather than emergency relief.
Class and exam questions
Can salmeterol be used to relieve an acute asthma attack?
No. The drug has a delayed onset of action (15–30 minutes) and reaches its peak only after 2–4 hours. Short-acting drugs with a rapid effect (e.g., salbutamol or fenoterol) are used for emergency relief.
What is the advantage of selective $\beta_2$-adrenomimetics over non-selective ones?
They act selectively on bronchial receptors, ensuring high bronchodilation efficacy upon inhalation administration, and lack the pronounced stimulating effect on the heart ($\beta_1$-receptors) characteristic of isoprenaline and orciprenaline.
Why are $\beta_2$-adrenomimetics combined with anticholinergics?
This combination provides synergy (mutual enhancement of the bronchodilator effect) and allows for a reduced dose of the adrenomimetic, which decreases the risk of side effects.
How does salmeterol affect the inflammatory process in the bronchi?
The drug prevents mast cell degranulation, thereby inhibiting the release of inflammatory and allergic mediators in the respiratory tract.
What else to study on this topic
- Comparative pharmacokinetics of inhalational $\beta_2$-adrenomimetics
- Mechanism of synergy development between $\beta_2$-adrenomimetics and anticholinergics
- Effect of adrenomimetics on mucociliary clearance
- Differences between salmeterol and formoterol in clinical practice
- Non-selective $\beta$-adrenomimetics: reasons for limiting their use
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