Theophylline

How it works

It produces bronchodilation through phosphodiesterase inhibition and adenosine-receptor antagonism, with additional anti-inflammatory and respiratory-stimulant effects.

Prescribing in practice

• It has a narrow therapeutic index, so plasma-level monitoring is required and small changes in dose or clearance can cause toxicity.
• Numerous interactions alter levels — smoking and certain enzyme inducers lower them, while macrolides, ciprofloxacin and cimetidine raise them; toxicity causes vomiting, arrhythmias and seizures.
• Modified-release preparations differ between brands and are not interchangeable — prescribe and dispense by brand.

Monitoring

Measure plasma theophylline at the recommended time after dosing once steady state is reached, and recheck after dose changes, when interacting drugs start or stop, or when smoking status changes; monitor for toxicity symptoms and low potassium.

Counselling the patient

• Always use the same brand and do not switch without advice.
• Tell health professionals you take theophylline before starting any new medicine, and inform them if you start or stop smoking.
• Report nausea or vomiting, palpitations, tremor or feeling agitated, which may indicate the level is too high.

Evidence & guidelines

An add-on bronchodilator in asthma and COPD reserved for when first-line inhaled therapies are insufficient, reflecting its narrow safety margin in UK respiratory guidance.