Aminophylline

How it works

It is a methylxanthine that inhibits phosphodiesterase and antagonises adenosine receptors, relaxing bronchial smooth muscle and enhancing respiratory function.

Prescribing in practice

• It has a narrow therapeutic index with a risk of arrhythmias and convulsions, and serum theophylline concentrations must guide dosing.
• Numerous drug interactions and factors such as smoking, heart failure and hepatic impairment markedly alter clearance.
• Loading regimens differ in patients already taking oral theophylline, so prior therapy must be established before intravenous loading.

Monitoring

Monitor serum theophylline concentrations, heart rate and rhythm, and serum potassium, particularly during intravenous use.

Counselling the patient

• Report palpitations, persistent vomiting, tremor or seizures promptly.
• Tell clinicians if your smoking habits change as this alters how the drug is handled.
• Do not change brands or formulations without advice.

Evidence & guidelines

Therapeutic drug monitoring of theophylline is well established owing to its narrow margin between effective and toxic concentrations.