Theophylline (Aminophylline)

Clinical Chemistry

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Description

Theophylline ( 1,3-dimethylxanthine ) is a naturally occurring compound with bronchodilator effects that is used in the treatment of asthma. Because of the narrow therapeutic index and the wide interindividual variability in the rate of theophylline metabolism and clearance, serum concentrations may be useful. Theophylline elimination is slowed in obese patients, patients with hepatic disease, and in those on a high carbohydrate, low protein diet. Premature infants have very low rates of theophylline elimination. Conversely, theophylline elimination is more rapid among cigarette smokers ( Roche data ). In chronic theophylline therapy, samples should be taken when the patient has attained a steady state ( 2 to 3 days after last dose change ). In IV aminophylline therapy, samples should be taken 1 to 4 hours after loading dose, and between 3 and 18 hours ( 1 to 2 half-lives ) to enable dose adjustment if required.

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Indications

Measurement of theophylline may be useful in the following circumstances: - dose optimisation - uncontrolled respiratory disorders or suspected toxicity - in patient populations with greater metabolic variability/polypharmacy ( children, pregnancy, elderly, severe intercurrent illness ). In pregnancy, theophylline measurement is recommended in patients with acute severe asthma and in patients whose effective treatment is critically dependent on serum theophylline concentration ( SIGN guidelines ). - where the formulation of the drug is altered - where there is the possibility of drug interactions - in excerbation of COPD, measure theophylline on hospital admission ( for patients already on theophylline ) and within 24 hours of starting treatment in patients commencing IV aminophylline ( NICE guidelines ). - in life-threatening asthma, measure theophylline in patients already receiving theophylline prior to commencement of IV aminophylline. Serum theophylline concentrations should be measured daily in patients receiving IV aminophylline for more than 24 hours ( SIGN guidelines ).

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Sample Type

Serum SST/Gel, minimum 2mL (1mL separated serum). Sample timing varies with formulation

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Reference Range

Reference ranges are provided on the report. Alternatively, please contact the laboratory for current ranges.

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Turnaround Time

24 hours

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Testing Frequency

Daily

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External Notes

Ideally sample pre-dose for therapeutic drug monitoring (TDM) purposes.  However, different sustained release preparations may have different monitoring requirements, and advice should be sought from the product literature or Pharmacy if required.  In cases of suspected toxicity, please indicate time of last dose and sample collection.  See indications section for details of sampling recommended in specific clinical scenarios.

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Patient Preparation

For TDM purposes, take samples pre-dose ( ideally ). Patients should have attained steady-state ( see below ) prior to sample collection.

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Please note: the above information is subject to change and we endeavour to keep this website up to date wherever necessary.