Onset of Action of Terbutaline
Terbutaline begins working within 5 minutes when administered by inhalation for acute bronchospasm relief. 1, 2
Route-Specific Onset Times
Inhaled Terbutaline (Fastest)
- Onset of action: 5 minutes when administered via metered-dose inhaler or nebulizer 1, 2
- Provides the most rapid bronchodilation compared to other routes of administration 1
- Peak effect occurs within 30-60 minutes 3
- Duration of action: 4-6 hours 3
Subcutaneous Terbutaline
- Onset of action: within 5 minutes at doses of 0.25-0.50 mg 1
- The American Heart Association guidelines note terbutaline can be given subcutaneously at 0.25 mg, repeated every 20 minutes for up to 3 doses in acute severe asthma 3
- However, there is no evidence that subcutaneous terbutaline has advantages over inhaled β2-agonists 3
Clinical Implications
Why Inhaled Route is Preferred
- Inhaled terbutaline offers the fastest onset, maximal response, and longest duration compared to subcutaneous or oral routes 1
- Produces fewer cardiovascular side effects (less tachycardia and tremor) than subcutaneous administration 4, 5
- When delivered via spacer device, inhaled terbutaline is at least as effective as subcutaneous adrenaline for acute severe asthma, with better tolerability 4
Important Caveats
- The dose delivered by inhalation depends on the patient's lung volume and inspiratory flow rate 3
- Proper inhaler technique must be demonstrated and rechecked periodically, as many patients use inhalers incorrectly 3
- If metered-dose inhaler technique is inadequate, consider using a spacer device or nebulizer 3, 4
- Regular use (≥4 times daily) does not affect potency but reduces duration of action 3