Short-acting beta-2 agonists

SABAs stimulate the beta-2 receptors of airway smooth muscle. Through a G protein the receptor switches on adenylyl cyclase; the rise in cyclic AMP activates protein kinase A, which lowers calcium inside the cell and relaxes the muscle from the trachea down to the smallest bronchioles. Inhaled, they open the airways almost at once and work for 4 to 6 hours, so they serve as relievers.

• SalbutamolWith terbutaline it is one of the two main reliever inhalers: it works almost at once and lasts 4 to 6 hours.
• TerbutalineLike other beta-2 agonists it relaxes the uterus, but it is not approved for delaying labor beyond 48 to 72 hours because of serious harm to mothers.

• Quick relief of asthma symptoms
• Preventing exercise-induced bronchospasm
• Relief of breathlessness in COPD

• Shaky hands (tremor)Known for
• Fast heartbeat and palpitationsKnown for
• Headache
• Nervousness and restlessness
• Muscle cramps
• Low potassium (hypokalemia)Serious
• Raised blood sugar
• Irregular heart rhythmsSerious
• QT prolongation on the ECG
• Paradoxical bronchospasmSerious

What the class has in common. Each drug's card has its own, and Known for marks what an exam expects you to know.

• Needing a reliever more often signals worsening asthma that needs anti-inflammatory treatment such as a steroid.
• Beta blockers block their effect and can cause severe bronchospasm in asthma.
• Loop and thiazide diuretics, steroids and theophylline add to the fall in potassium.
• Care in heart disease, arrhythmia, hypertension, hyperthyroidism, diabetes or seizure disorders.

Written for biofideX in plain words, after checking these references:

• Albuterol sulfate HFA inhalation aerosol: label (DailyMed)
• Terbutaline sulfate injection: label (DailyMed)
• Albuterol (NCI Thesaurus)
• Salbutamol inhalers (NHS)

For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.