Fenoterol hydrobromide: Salt form of fenoterol as a short acting beta 2 sympathomimetic
Fenoterol hydrobromide is the salt form of fenoterol commonly used in pharmaceutical preparations, a short to medium acting beta 2 sympathomimetic (SABA, short acting beta 2 agonist). Well known brand names are Berotec (inhalation for asthma and COPD) and Partusisten (intravenous and oral as a tocolytic agent in obstetrics).
Fenoterol was one of the first selective beta 2 agonists and has a long history in asthma and COPD therapy. In modern pulmonology, fenoterol today is largely replaced by salbutamol or formoterol because it shows a somewhat less favorable cardiovascular adverse effect profile. In obstetrics, however, fenoterol as an intravenous tocolytic agent continues to play an important role in inhibiting labor in preterm labor situations. A detailed pillar page on the active substance itself can be found at /wirkstoff/fenoterol.
Mechanism of action and salt form
The hydrobromide salt is formed by protonation of the nitrogen base in the fenoterol molecule and binding of a bromide ion. The salt is well water soluble and chemically stable, which is why it represents the active form in virtually all pharmaceutical formulations. Pharmacologically, it dissociates immediately in the body into fenoterol and bromide, so the effect is carried exclusively by fenoterol.
Fenoterol binds to beta 2 adrenergic receptors in the smooth muscle of the airways and uterus. Through activation of adenylyl cyclase and elevation of intracellular cAMP, the smooth muscle relaxes, leading to bronchodilation in the airways and tocolysis (labor inhibition) in the uterus.
Compared to salbutamol, fenoterol has somewhat lower beta 2 selectivity, which at higher doses can lead to increased beta 1 effects on the heart (tachycardia, increased inotropic effect). Pharmacokinetically, fenoterol hydrobromide becomes effective locally rapidly after inhalation, with onset of action within 5 minutes and duration of action 4 to 6 hours. After intravenous administration, the effect is virtually immediate.
Indications
- Acute bronchospasm in asthma: reliever therapy in acute attacks, in emergency situations
- COPD exacerbation: acute relief of shortness of breath
- Bronchospasm provocation: as a bronchodilator before lung function testing
- Tocolysis (labor inhibition) as Partusisten: in threatened preterm labor to delay delivery for 24 to 48 hours in order to achieve efficacy of fetal lung maturation with glucocorticoids
- Acute fetal distress situation: short term tocolysis with pathological CTG in preparation for emergency operation
- Threatened uterine rupture during labor: as short term tocolysis
Dosage and administration
Inhalation acute (Berotec): 1 to 2 puffs (100 to 200 micrograms) when short of breath, if necessary repeat after 5 minutes. Maximum 8 puffs per day, with higher requirement medical reevaluation.
Tocolysis intravenous (Partusisten): Initially 0.5 to 1 microgram/minute as continuous infusion, adjustment based on contraction frequency and maternal tolerance. Maximum dose 4 micrograms/minute. Therapy typically over 48 hours, then discontinuation attempt.
In renal insufficiency and hepatic insufficiency: choose dose cautiously, as accumulation and cardiovascular adverse effects may increase.
Adverse effects
Frequent (inhalation): tremor (especially fine hand tremor), tachycardia, palpitations, headache, restlessness, dry mouth, local irritation of oral and pharyngeal mucosa.
Frequent (intravenous tocolysis): maternal tachycardia, tremor, sweating, nausea, hypokalemia, hyperglycemia, hypotension. In the fetus reactive tachycardia.
Serious, rare: pulmonary edema (especially with prolonged tocolysis with continuous volume administration), cardiac arrhythmias including atrial fibrillation, myocardial ischemia in those with pre existing cardiac disease, severe hypokalemia with convulsion or arrhythmia, paradoxical bronchospasm inhalation.
Important: patients under inhalation SABA therapy should be presented to a physician if there is increasing need, as more frequent reliever requirement indicates inadequate asthma control and increases the risk of severe asthma attacks.
Drug interactions
- Other sympathomimetics: additive cardiovascular effects, caution
- Beta blockers (especially non selective such as propranolol): antagonism of bronchodilation, contraindicated in asthma
- Diuretics and glucocorticoids: additive hypocalcemia and hypokalemia
- Theophylline: additive tachycardia and tremor
- MAO inhibitors and tricyclic antidepressants: enhanced cardiovascular effect
- Volatile inhalation anesthetics (halothane, sevofluran): risk of serious arrhythmias
Special notes
Pregnancy: in tocolysis indication deliberately desired, otherwise use with restraint. Inhalation use is considered safe in pregnancy because systemic absorption is low.
Breast feeding: inhalation use is safe. Intravenous high dose therapy only under strict indication.
Tocolysis risks: use as labor inhibitor in obstetrics takes place under inpatient conditions with continuous maternal and fetal monitoring (CTG, blood pressure, heart rate, electrolytes). With maternal tachycardia over 120 beats/minute, pulmonary edema or chest pain immediate treatment discontinuation.
Asthma stewardship: SABA such as fenoterol are relievers, not controllers. Frequent use (more than 2 times per week) indicates inadequate controller therapy and should be discussed with the practice. Current GINA recommendations prefer ICS-LABA combinations instead of pure SABA monotherapy.
You might also be interested in
- Fenoterol, detailed pillar page on the active substance
- Salbutamol, classic short acting beta 2 sympathomimetic
- Formoterol, long acting beta 2 sympathomimetic (LABA)
- Atosiban, oxytocin receptor antagonist as alternative tocolytic
- Budesonid, inhalation glucocorticoid for fetal lung maturation
Frequently asked questions
What is the difference between fenoterol and fenoterol hydrobromide?
Pharmacologically none. Fenoterol hydrobromide is the water soluble salt form used in almost all pharmaceuticals. In the body it dissociates immediately into the active fenoterol and bromide.
Why should I not use fenoterol too often?
Frequent SABA requirement indicates inadequately controlled asthma or COPD. Studies have shown that intensive SABA use is associated with increased mortality in asthma. Current guidelines (GINA) recommend an ICS-LABA combination as basic therapy instead of SABA monotherapy. If more than 2 SABA inhalations per week are needed, asthma therapy should be reviewed.
How long does tocolysis with Partusisten last?
Intravenous tocolysis with fenoterol is typically given for 24 to 48 hours in order to achieve full efficacy of maternal fetal lung maturation with glucocorticoids. Prolongation beyond 48 hours provides no clear benefit and increases risks (pulmonary edema, cardiovascular complications).
Can asthma inhalers affect the heart?
Yes. Beta 2 sympathomimetics such as fenoterol have cardiovascular effects at higher doses or with frequent use (tachycardia, palpitations, in rare cases arrhythmias). In patients with coronary heart disease, hypertension or atrial fibrillation, use should be cautious and taking into account concomitant medication.
Sources
- Gelbe Liste, Fenoterol active substance profile
- GINA Global Initiative for Asthma Recommendations
- DGGG Guideline Preterm infants and tocolysis
- BfArM, Federal Institute for Drugs and Medical Devices
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