Mechanism of Action
The pharmacological effects of hexoprenaline are mediated by the selective stimulation of $\beta_2$-adrenergic receptors. In the smooth muscle of the uterus (myometrium) and bronchi, this leads to the activation of adenylate cyclase, accumulation of cAMP, and a decrease in intracellular free calcium concentration. As a result, myometrial tone and contractile activity decline. Additionally, $\beta_2$-receptor stimulation prevents mast cell degranulation, inhibiting the release of inflammatory mediators and improving mucociliary clearance.
Pharmacological Effects and Kinetics
Hexoprenaline is classified as a short-acting $\beta_2$-adrenergic agonist (duration of action is 4–6 hours). The drug features a short latent period: the onset of bronchodilatory or tocolytic effects is observed within 2–5 minutes after administration, with peak action developing in 40–60 minutes. The drug effectively dilates bronchi and reduces uterine contractility, making it a valuable tool in emergency settings.
Indications for Use
In clinical and obstetric practice, hexoprenaline is prescribed for:
- Suppressing labor contractions and preventing preterm labor;
- Managing threatened abortion;
- Relieving excessive labor activity;
- Management and prevention of acute bronchospasm attacks (as a bronchodilator).
Administration Features and Fetal Effects
Routes of administration depend on the clinical scenario: for elective use, the drug is administered orally in tablets, whereas in emergency cases, it is given intravenously.
In obstetrics, hexoprenaline (alongside fenoterol) is considered a drug of choice because it carries a lower risk of adverse fetal effects compared to salbutamol. Nevertheless, drugs in this class cross the placental barrier and can induce fetal tachycardia and arrhythmias.
Administration and Dosage
Orally, the single dose (SD) is 0.0005 g (500 mcg tablets). For emergency suppression of labor contractions, the ampoule solution (10 mcg) is pre-diluted in 10 mL of 0.9% sodium chloride solution and administered slowly intravenously over 5–10 minutes.