1. Clinical Overview
Levosalbutamol is the (R)-enantiomer of the racemic drug salbutamol. It is a selective, short-acting beta-2 adrenergic receptor agonist (SABA) used as a bronchodilator for the relief and prevention of bronchospasm. In the Indian context, it is widely prescribed for reversible obstructive airway diseases. It offers a potentially improved therapeutic index over racemic salbutamol, with similar efficacy but a lower incidence of side effects like tachycardia and tremor, as the (S)-enantiomer is considered pharmacologically inactive and may contribute to adverse effects.
| Onset | Duration | Bioavailability |
|---|---|---|
| Within 5-10 minutes of inhalation. | Approximately 3 to 6 hours. | Approximately 10-25% of the inhaled dose reaches the lower respiratory tract; systemic bioavailability via inhalation is low. |
2. Mechanism of Action
Levosalbutamol selectively stimulates intracellular adenyl cyclase, the enzyme that catalyzes the conversion of adenosine triphosphate (ATP) to cyclic-3',5'-adenosine monophosphate (cAMP). Increased cAMP levels trigger a cascade leading to relaxation of bronchial smooth muscle.
3. Indications & Uses
- Treatment and prevention of bronchospasm in patients with reversible obstructive airway disease (e.g., Asthma).
- Relief of acute bronchospasm (as a rescue medication).
4. Dosage & Administration
Adult Dosage: For relief of acute symptoms: 50-100 mcg (1-2 puffs) by MDI as needed, not to exceed recommended maximum. For prevention: 50-100 mcg (1-2 puffs) 15-20 minutes before exercise or allergen exposure.
Administration: Shake inhaler well before use. Exhale fully. Place mouthpiece in mouth, seal lips around it. Start to inhale slowly and deeply, then press the canister to release medication. Continue to inhale deeply. Hold breath for about 10 seconds, then exhale slowly. Wait at least 30-60 seconds before second puff. Rinse mouth with water after use to prevent oral thrush. For spacer use, attach spacer to MDI, press canister once, inhale slowly from spacer, hold breath.
5. Side Effects
Common side effects may include:
- Headache
- Mild tremor (usually hands)
- Throat irritation or dryness
- Mild cough
- Palpitations
- Muscle cramps
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Non-selective Beta-blockers (e.g., Propranolol) | Antagonize bronchodilator effect; may cause severe bronchospasm in asthmatics. | Major |
| Diuretics (e.g., Furosemide, Hydrochlorothiazide) | Enhanced risk of hypokalemia due to additive effect. | Moderate |
| Digoxin | Hypokalemia may increase risk of digoxin toxicity (arrhythmias). | Moderate |
| Monoamine Oxidase Inhibitors (MAOIs) & Tricyclic Antidepressants (TCAs) | May potentiate cardiovascular effects (tachycardia, hypertension). | Moderate |
| Other Sympathomimetics (e.g., Decongestants) | Additive cardiovascular side effects (tachycardia, hypertension). | Moderate |
| Xanthine derivatives (e.g., Theophylline) | Increased risk of hypokalemia and potential additive cardiac effects. | Moderate |
7. Patient Counselling
- DO use this inhaler exactly as prescribed by your doctor.
- DO use it as a 'reliever' for sudden breathlessness or wheezing.
- DO rinse your mouth with water and spit it out after each use to prevent fungal infection.
- DO keep your inhaler clean. Wash the plastic mouthpiece with warm water weekly.
- DO carry your inhaler with you at all times.
- DONT exceed the recommended number of puffs in 24 hours.
- DONT stop your 'preventer' or 'controller' medications (like steroids) even if you feel well.
- DONT use this inhaler to treat cough or breathlessness not related to asthma/COPD without consulting a doctor.
8. Toxicology & Storage
Overdose: Exaggeration of known side effects: angina pain, hypertension or hypotension, tachycardia (rate up to 200 bpm), arrhythmias, nervousness, headache, tremor, muscle cramps, dry mouth, palpitations, nausea, dizziness, fatigue, malaise, hypokalemia, hyperglycemia, metabolic acidosis.
Storage: Store at room temperature (15-30°C). Protect from direct sunlight, heat, and frost. Do not puncture or incinerate the canister, even when empty. Keep out of reach of children. The canister is pressurized; do not expose to temperatures above 50°C.