Selective β2 Stimulants

SELECTIVE β₂ STIMULANTS

These include, salbutamol, terbutaline, salmeterol, formoterol and ritodrine. They cause bronchodilatation, vasodilatation and uterine relaxation, without producing significant cardiac stimulation. β₂ selectivity is only relative. Salbutamol has β₂:β₁ action ratio of about 10. They are primarily used in bronchial asthma. Other uses are:

As uterine relaxant to delay premature labour. Ritodrine is the preferred drug;

    In hyperkalaemic familial periodic paralysis— β₂ agonists benefit by enhancing K+ uptake into muscles → lowering plasma K+ levels.

The most important side effect is muscle tremor; tachycardia and arrhythmias are less likely.

Isoxsuprine

It is an orally effective long acting selective β receptor stimulant which has direct smooth muscle relaxant property as well. It has been used as uterine relaxant for threatened abortion and dysmenorrhoea, but efficacy is poor. Beneficial effects in peripheral and cerebral vascular diseases are disappointing.

Side effects: nausea, tachycardia, flushing, hypotension, dizziness, tremor.

Dose: 5–10 mg oral, i.m. 4–6 hourly, DUVADILAN 10 mg tab, 40 mg SR cap, 10 mg/2 ml inj.