Westhroid
Westhroid
Generic Name
Westhroid
Mechanism
- Selective β2‑adrenergic receptor agonist that binds to β2 receptors on bronchial smooth muscle cells.
- Activates Gs‑protein → adenylate cyclase → ↑ intracellular cAMP.
- cAMP phosphorylates protein kinase A (PKA), leading to phosphorylation of myosin light‑chain kinase (MLCK) and inhibition of its activity.
- Result: relaxation of bronchial smooth muscle, reversal of bronchospasm, and reduction of airway hyperresponsiveness.
- Minor systemic absorption produces modest elevations in heart rate and peripheral vasodilation.
Pharmacokinetics
| Parameter | Typical Value |
| Route | Inhalation (nebulizer or DPI) |
| Bioavailability | ~60 % (inhaled), ~80 % (nebulized) |
| Absorption | Rapid, peak plasma concentration (~15–20 min post‑nebulization) |
| Distribution | Widely distributed; volumes of distribution ~0.8 L/kg |
| Metabolism | Hepatic CYP3A4 (phase II glucuronidation) |
| Half‑life | 2–3 h (systemic). Bronchial effects last ~4–5 h. |
| Excretion | Renal (≈30 %) and biliary (~60 %) |
Drug–drug interactions: CYP3A4 inhibitors (ketoconazole, clarithromycin) increase systemic exposure → higher risk of tachycardia, tremor. Conversely, strong CYP3A4 inducers (rifampin, carbamazepine) may decrease efficacy.
Indications
- Acute bronchospasm in asthma (both episodic and persistent).
- Exacerbations of COPD and *asthma–COPD overlap* syndromes.
- Status asthmaticus refractory to conventional β‑agonists.
> *Guidelines*: Supported by the 2023 GINA and 2024 GOLD recommendations for rescue inhalers.
Contraindications
- Absolute contraindication: Severe uncontrolled tachyarrhythmias; decompensated or ischemic heart disease.
- Relative: Hypertension, hyperthyroidism, pheochromocytoma.
- Caution: Use with caution in patients on sympathomimetics (epinephrine) or sepsis requiring high‑dose vasopressors.
- Pregnancy/lactation: Classified as category C; risk/benefit assessment.
Dosing
| Form | Dose | Frequency | Max daily dose | Administration notes |
| Dry‑Powder Inhaler (DPI) | 2–4 puffs (90 µg/puff) | Every 2 h as needed | 12 puffs/day | Ensure proper inhalation technique; rinse mouth after use to reduce oral candidiasis. |
| Nebulizer solution | 0.4 mg/mL (10 mL per dose) | Every 2 h as needed | 48 mg/day | Use jet nebulizer with a mouthpiece; monitor for local irritation. |
> Practical tip: Administer 2 puffs/ministry of alveolar achieve systemically minimal concentrations and prompt bronchodilation.
Adverse Effects
| Adverse Effect | Frequency | Management |
| Tremor | 15–25 % | Patient counseling; dose reduction if needed |
| Tachycardia / Palpitations | 10–20 % | ECG monitoring in high‑risk patients; consider β1‑blocker therapy in safe patients |
| Hypokalemia | <5 % | Baseline potassium measurement; supplement if <3.5 mmol/L |
| Headache | 5 % | Symptomatic relief |
| Oral candidiasis (DPI) | 2 % | Antifungal mouthwash |
| Paradoxical bronchospasm | <1 % | Discontinue immediately; switch to epinephrine or methylxanthines |
| Arrhythmia | <1 % | Continuous cardiac monitoring in ICU; discontinue if sustained arrhythmia develops |
Monitoring
- Vital signs: pulse, BP, RR after each dose in patients >55 y or with cardiac disease.
- Electrocardiogram (ECG): baseline and every 4 hrs for high‑risk patients.
- Serum potassium: baseline, then days 1–3 if on long‑term therapy.
- Blood glucose: in diabetics due to mild hyperglycemia.
- Peak expiratory flow (PEF): for severe asthma patients during rescue therapy.
Clinical Pearls
- Use as rescue, not maintenance: Westhroid’s short action warrants use in acute exacerbations; combine with long‑acting bronchodilators (LABAs) and inhaled corticosteroids for maintenance.
- Avoid in comorbid hypertension: Monitor BP closely; consider antihypertensives if necessary.
- Leverage its rapid onset: When nebulizer is unavailable, a DPI (2 puffs) can be used as an on‑call foliate.
- CYP3A4 interaction: In patients on ketoconazole, halve the dose to mitigate cardiovascular side effects.
- Mark as first‑line in status asthmaticus: Where β2‑agonist tolerance is suspected, follow GINA’s stepwise protocol and add magnesium sulfate or epinephrine.
- Patient education: Demonstrate inhaler technique; improper inhalation leads to subtherapeutic dosing. Ensure patients receive a dosing diary.
- Switch motivation: When patients struggle with inhaler compliance, switch to nebulized format temporarily to improve symptom control.
> *Clinical practice guideline support*: The 2023 GINA step‑4 therapy for asthma includes *“inhaled short‑acting β2‑agonists”* as necessary rescue. Westhroid’s pharmacologic profile matches the step‑2 rescue criteria, making it an optimal agent for acute indications.
--
• *This drug card summarizes current evidence and guideline recommendations. Always consult the product insert for patient‑specific contraindications and dosage specifics.*