Theophylline has a narrow margin between therapeutic and toxic effects and different brands of modified-release theophylline have different bioavailability. Therefore the brand to be dispensed must be specified.
Uniphyllin Continus® has been selected on basis of uniformity of drug release and cost, patients maintained on other theophylline preparations should not be changed. If the patient experiences side effects with Uniphyllin Continus® another preparation may be tried.
If a prescription for a modified-release oral theophylline preparation does not specify a brand name the pharmacist should contact the prescriber and agree the brand to be dispensed. Additionally, it is essential that when a patient is discharged from hospital the patient is maintained on the brand that he/she was stabilised on as an in-patient.
There is an increased risk of hypokalaemia when theophylline is given with high doses of beta2 agonists.
Theophylline is metabolised in the liver. The plasma theophylline concentration is increased in heart failure, hepatic impairment, viral infections, in the elderly and by drugs that inhibit its metabolism. The plasma theophylline concentration is decreased in smokers, by alcohol consumption and by drugs that induce its metabolism.
Smoking cessation may increase theophylline levels. This is independent of any nicotine replacement therapies that may be prescribed.
Theophylline levels should be checked mainly to avoid toxicity and to ascertain compliance (very low/absent level). Theophylline dose otherwise should be titrated based on symptom relief. For further details on monitoring see the BNF.