Formoterol

Formoterol is a selective beta-2 adrenergic receptor agonist that relaxes bronchial smooth muscle and dilates the airways. Its high lipophilicity allows partitioning into the cell membrane, creating a membrane depot that supports a 12-hour duration of action, while a hydrophilic side chain enables rapid receptor engagement and a 2–3-minute onset — a combination that justified its place in the modern maintenance-and-reliever approach to asthma management.

Mechanism of Action

• Beta-2 receptor agonism: formoterol binds the β2-adrenergic receptor on airway smooth muscle, activating Gs proteins and adenylyl cyclase, which converts ATP to cyclic AMP. Elevated intracellular cAMP activates protein kinase A, leading to relaxation of bronchial smooth muscle and bronchodilation.
• Selectivity: approximately 200-fold greater activity at β2 receptors than at β1 receptors, minimising (but not eliminating) cardiac stimulation. Residual β1 agonism explains the dose-dependent tachycardia and tremor seen at high doses.
• Additional effects: inhibition of mast-cell mediator release (histamine, leukotrienes, prostaglandins), reduction of airway smooth muscle hyperresponsiveness, modulation of airway mucus secretion, and a small effect on ciliary clearance.
• Onset and duration: onset of bronchodilation ~2–3 minutes (comparable to salbutamol); duration ~12 hours.
• Why it must be combined with an ICS in asthma: LABA monotherapy in asthma is associated with increased risk of severe exacerbation and asthma-related death; co-administration with an inhaled corticosteroid eliminates this risk and addresses the underlying eosinophilic airway inflammation.

Pharmacokinetics

• Absorption: pulmonary bioavailability of an inhaled dose ~43%; total systemic bioavailability (including swallowed fraction) ~60%; rapidly absorbed, Tmax 0.5–2 hours.
• Protein binding: 31–38% (relatively low for inhaled bronchodilators); to albumin.
• Metabolism: primarily by direct glucuronidation (UGT1A1, UGT1A8, UGT1A9, UGT2B7, UGT2B15) and O-demethylation followed by glucuronidation (CYP2D6, CYP2C19, CYP2C9, CYP2A6). Metabolites are inactive.
• Half-life: inhaled terminal elimination half-life 7–10 hours; plasma half-life 1.7–2.3 hours after inhalation.
• Excretion: dose- and route-dependent — approximately 60% urinary and 25–35% faecal after systemic administration; in asthma after inhalation, ~10% in urine as unchanged drug, ~15–18% as direct glucuronides.
• Clearance: renal clearance ~157 mL/min after inhalation.

• Asthma: maintenance treatment in patients aged ≥6 years (formulation-dependent), exclusively as a fixed-dose combination with an inhaled corticosteroid (budesonide, beclometasone, mometasone, fluticasone). GINA strategy supports formoterol-containing ICS combinations both as scheduled maintenance and as the as-needed reliever (MART/SMART).
• Chronic obstructive pulmonary disease (COPD): maintenance bronchodilation as monotherapy, as a fixed-dose LABA + LAMA (with aclidinium or glycopyrronium), as ICS + LABA, or as triple ICS + LABA + LAMA combinations.
• Prevention of exercise-induced bronchospasm in patients ≥12 years — short-term, with continued ICS background therapy in asthma.

• Hypersensitivity to formoterol or any of the excipients (including milk protein in lactose-based DPIs for patients with severe milk-protein allergy).
• Asthma without concomitant inhaled corticosteroid — LABA monotherapy in asthma is contraindicated due to increased mortality risk.

Common (≥1/100 to <1/10): tremor (fine, postural), palpitations, tachycardia, headache, muscle cramps, throat irritation, dry mouth, cough.

Uncommon (≥1/1,000 to <1/100): nervousness, agitation, insomnia, dizziness, nausea, oropharyngeal candidiasis (with ICS combinations), hypokalaemia (high doses), hyperglycaemia, taste disturbance.

Rare (<1/1,000): cardiac arrhythmia (atrial fibrillation, supraventricular tachycardia, extrasystoles), angina pectoris, blood pressure variations, paradoxical bronchospasm, peripheral oedema, hypersensitivity reactions including rash and angioedema.

Very rare (<1/10,000): QTc prolongation, exacerbation of pre-existing arrhythmia.

• Other beta-adrenergic agonists (salbutamol, salmeterol, terbutaline): additive cardiovascular and metabolic effects; use only when clinically indicated.
• Beta-blockers, including ophthalmic timolol: may antagonise the bronchodilator effect — avoid where possible; cardioselective β1-blockers preferred if essential.
• MAO inhibitors, tricyclic antidepressants, and other QT-prolonging agents: increased risk of cardiovascular effects and arrhythmia.
• Diuretics (loop and thiazide), xanthines (theophylline), corticosteroids: additive hypokalaemia.
• Halogenated anaesthetics: increased risk of arrhythmia during general anaesthesia — discontinue formoterol before elective surgery where possible.
• Antidiabetic agents: high-dose β2 agonists raise blood glucose; monitor and adjust antidiabetic therapy.

Formoterol is administered exclusively by oral inhalation. Patients should be trained in correct inhaler technique for the specific device prescribed; technique varies substantially between DPIs (Turbuhaler, Aerolizer, Spiromax, Easyhaler, Genuair) and pMDIs.

Asthma (Fixed-Dose Combination with ICS)

• Adults and adolescents ≥12 years (e.g., budesonide/formoterol 200/6 μg or 160/4.5 μg): 1–2 inhalations twice daily for maintenance; additional inhalations as needed for symptom relief under the MART strategy, up to a manufacturer-specified daily maximum.
• Children 6–11 years: lower-strength combinations (e.g., budesonide/formoterol 100/6 μg or 80/4.5 μg) 1 inhalation twice daily.

COPD

• Monotherapy or in combination: 12 μg twice daily (single-agent DPI) or fixed-combination strengths twice daily.

Exercise-Induced Bronchospasm (≥12 Years)

• 12 μg by inhalation at least 15 minutes before exercise, on an occasional basis; not for daily prophylaxis.

Renal Impairment

No dose adjustment.

Hepatic Impairment

Caution in severe hepatic impairment due to reduced clearance.

Missed Dose

Take as soon as remembered unless close to the next scheduled dose. Do not double up. In MART regimens, scheduled doses are taken as planned and reliever doses are taken on symptoms.

LABA Safety in Asthma

Patients with asthma must use formoterol only in combination with an inhaled corticosteroid. Worsening asthma control, increased reliever use, or declining peak flow requires step-up of ICS, not simply additional formoterol.

Inhaler Technique

Demonstrate, observe, and re-check inhaler technique at every opportunity. Suboptimal inspiratory flow can severely reduce DPI lung deposition; poor coordination compromises pMDI delivery and may benefit from spacer use (for ICS-LABA pMDI products).

Paradoxical Bronchospasm

If wheeze or shortness of breath worsens immediately after inhalation, stop and use a short-acting bronchodilator; switch to an alternative agent.

Hypokalaemia and Hyperglycaemia

High doses, particularly in combination with xanthines, diuretics, or corticosteroids, can produce significant hypokalaemia and hyperglycaemia. Monitor in severe asthma exacerbations.

Cardiovascular Disease

Use with caution in patients with severe cardiovascular disease, particularly coronary insufficiency, tachyarrhythmia, severe heart failure, or QT prolongation.

Pregnancy and Lactation

• Pregnancy: data from inhaled use suggest no significant teratogenic risk; uncontrolled asthma carries greater risk than treatment. Use when clearly needed.
• Breastfeeding: small amounts excreted in breast milk; inhaled use compatible.

Effect on Driving

No or negligible influence at therapeutic doses. Patients experiencing dizziness should refrain.

Store below 25–30 °C depending on formulation. Protect from moisture (DPIs are particularly hygroscopic); replace device cap promptly. Do not store pMDI canisters near direct heat or sunlight.

Typically 2–3 years from manufacture for unopened devices. After-opening windows differ — DPI cartridges generally 3 months after first opening; pMDI canisters 3–6 months. Nebuliser ampoules must be used immediately after opening.

Prescription required (Rx).