Selective p2 agonists are usually given by inhalation via a pressurised aerosol or a nebulizer. Inhalation often gives rapid relief of bronchospasm, although the aerosol is of less benefit in severe asthma.

Nebulized drugs require a minimum volume of 4ml and a driving gas flow of 6-8l/min.

In extremis, epinephrine may be used IV, SC or injected down the endotracheal tube. As epinephrine is not selective, arrhythmias are more likely. However, the a agonist effect may reduce mucosal swelling by vasoconstriction.

Ipratropium bromide has no systemic effects and does not depress mucocilliary clearance. It is synergistic with p2 agonists but has a slower onset of action.

Aminophylline is synergistic with p2 agonists. Dosages must be adjusted according to plasma levels (range 10-20mg/l) since toxic effects may be severe. Dose requirements are reduced by heart failure, liver disease, chronic airflow limitation, fever, cimetidine, erythromycin. Dose requirements are increased in children, smokers and those with a moderate to high alcohol intake.

Coping with Asthma

Coping with Asthma

If you suffer with asthma, you will no doubt be familiar with the uncomfortable sensations as your bronchial tubes begin to narrow and your muscles around them start to tighten. A sticky mucus known as phlegm begins to produce and increase within your bronchial tubes and you begin to wheeze, cough and struggle to breathe.

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