Fenoterol

BRAND NAMES

1. Berotec (most widely known international brand) 

2. Partusisten (used especially in obstetric settings in some countries) 

3. Berotec N (inhalation aerosol formulation)

MECHANISM OF ACTION

Fenoterol is a short-acting β2-adrenergic receptor agonist. It stimulates β2 receptors in bronchial smooth muscle, leading to activation of adenylate cyclase and increased cyclic AMP (cAMP). This causes relaxation of bronchial smooth muscles, resulting in bronchodilation and improved airflow in conditions like asthma and COPD. At higher doses, it may also stimulate β1 receptors, contributing to cardiovascular effects such as tachycardia.

PHARMACOKINETICS

Absorption

Fenoterol is rapidly absorbed after inhalation, with quick onset of action (within minutes). When administered orally, absorption is less efficient due to first-pass metabolism.

Distribution

Fenoterol is distributed into lung tissues where it acts on airway smooth muscle. Plasma protein binding is moderate, and systemic distribution is limited compared to inhaled effect.

Metabolism

Fenoterol is metabolized in the liver primarily through conjugation (sulfation). It does not undergo extensive oxidative metabolism via cytochrome P450 enzymes.

Elimination

Fenoterol and its metabolites are excreted mainly via the kidneys in urine. The elimination half-life is relatively short, supporting its use as a short-acting bronchodilator.

PHARMACODYNAMICS

Fenoterol selectively activates β2-adrenergic receptors in the lungs, leading to smooth muscle relaxation and bronchodilation. It reduces airway resistance, relieves bronchospasm, and improves oxygen flow. At higher systemic exposure, it may also affect cardiac β receptors, leading to increased heart rate and tremors.

ADMINISTRATION

Fenoterol is administered mainly by inhalation using metered-dose inhalers or nebulized solutions. It is used for rapid relief of acute bronchospasm. Oral and parenteral forms exist in some settings but are less commonly used due to higher systemic side effects.

DOSAGE AND STRENGTH

Dosage depends on severity of bronchospasm and patient response. Inhaled doses are typically given as needed for symptom relief, while nebulized solutions are used in acute emergency care. Overuse should be avoided due to risk of adverse cardiovascular effects.

DRUG INTERACTIONS

Fenoterol may have increased cardiovascular effects when used with other sympathomimetics. Beta-blockers can reduce its bronchodilating effect. Caution is required when used with drugs that affect potassium levels, as hypokalemia may be enhanced.

FOOD INTERACTIONS

No significant food interactions are known with fenoterol. However, stimulants such as caffeine may enhance side effects like tremors or palpitations.

CONTRAINDICATIONS

Fenoterol is contraindicated in patients with hypersensitivity to the drug. It should be used cautiously in patients with cardiovascular disorders such as arrhythmias, hypertension, or ischemic heart disease.

SIDE EFFECTS

• Tremors

• Palpitations

• Headache

• Nervousness

• Tachycardia

• Muscle cramps

• Rare: hypokalemia

 OVER DOSAGE

Overdose of fenoterol occurs due to excessive use of inhaled or systemic doses and leads to overstimulation of β2 (and partly β1) adrenergic receptors. The most common effects are marked tachycardia, palpitations, tremors, anxiety, and headache.

TOXICITY

Overdose of fenoterol can lead to excessive β-adrenergic stimulation, resulting in severe tachycardia, arrhythmias, hypertension or hypotension, tremors, and hypokalemia. In severe cases, it may cause cardiovascular collapse. Treatment is supportive, with careful monitoring of heart rhythm and electrolytes, and discontinuation of the drug.