Xanthines

Aminophylline is a combination of theophylline and ethylenediamine which confers greater solubility in water but can cause an allergic reaction. Intravenous aminophylline may be used in the treatment of very severe asthma attacks.

Theophylline must be prescribed by brand as products are not equivalent.

Theophylline liquid should only be used if there are swallowing difficulties. This is not a sustained release preparation so dosage adjustments will need to be made if patients are switched from modified release formulations.

Slo-phyllin^® capsules can be opened and the contents (enteric-coated granules) poured through the feeding tube, flushing before and after with 15-30mL of water. The granules have also been administered on soft food for patients with swallowing difficulties. The granules should not be chewed or crushed, and therefore this method may not be appropriate for patients with limited understanding or impaired ability to follow instructions. Do NOT crush the modified-release tablets.

Therapeutic drug monitoring of theophylline is essential as there is a narrow therapeutic margin. There is considerable variation in half life particularly in smokers and those with hepatic impairment or heart failure.

A plasma theophylline level 10-20mg/litre is appropriate for most patients