Theophylline (Formulary)

• Keep patients on the same brand of modified-release theophylline as there are differences in bioavailability between brands; the same dose of different brands may not be therapeutically equivalent.
• Theophylline has a narrow therapeutic range therefore therapeutic drug monitoring is advised when initiating therapy and thereafter as clinically indicated (eg dose changes, introduction of long-term interacting drug).
• Monitor plasma theophylline concentration at least 5 days after initiation or changing the oral dose or immediately after an intravenous aminophylline loading dose. Sample 4 to 6 hours after an oral dose (not critical).  See Therapeutic drug monitoring guidance.
• Theophylline can cause arrhythmias; check plasma concentration in the event of any new cardiac symptoms.
• Important interactions exist with other drugs; some may produce theophylline toxicity (eg clarithromycin, ciprofloxacin), others may decrease plasma levels (eg antiepileptics, rifampicin).

Oral theophyllines are weak bronchodilators with a high incidence of side-effects and are now less commonly used.  Uniphyllin Continus^® is the recommended preparation and should be used for all patients who are being commenced on theophylline for the first time.  For advice on therapeutic monitoring of theophylline/aminophylline, refer to Therapeutic drug monitoring guidance.