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Using this page · Individualise medicines monitoring

This medicines monitoring page has been written using publications and expert opinion. It is designed to save clinician time, but not replace professional responsibility. When using this page you should: ensure an individualised monitoring plan is developed in partnership with the patient and take account of any locally agreed advice and guidance.

Before starting


  • Baseline
    • Liver function tests
    • Urea and electrolytespotassium particularly important
    • Smoking statusadvise patients to seek advice if likely to change

After started or dose changed


  • 5 days after starting treatment; 3 days after any dose adjustment
    • Plasma theophylline concentrationfor MR preparations, take levels 4-6 hours after dose

Theophylline levels, dosing, and adverse effects

Theophylline levels

In most individuals a plasma theophylline of between 10-20mg/litre is required for satisfactory bronchodilation; however, a lower plasma theophylline concentration of 5-15mg/litre (or less) may sometimes be effective.


Lower than normal doses may be required in older people, those with heart failure, or those with hepatic impairment.

Adverse effects

Adverse effects can occur within the range 10-20mg/litre and both the frequency and severity increase at concentrations above 20mg/litre.

Ongoing once stable


  • Every 6 - 12 months
    • Plasma theophylline concentrationincrease frequency or monitor one-off for some patients; for MR preparations, take levels 4-6 hours after dose

Increasing monitoring frequency

Consider increasing frequency of monitoring in patients who are:

  • older
  • have heart failure
  • have hepatic impairment
  • pregnant

Monitoring one-off for some patients

Consider checking plasma theophylline where the patient:

  • experiences side effects that may suggest toxicity (nausea, vomiting, tremor or palpitations)
  • starts an enzyme-inhibiting drug (e.g. erythromycin, clarithromycin, allopurinol, or cimetidine)
  • starts an enzyme-inducing drug (e.g. carbamazepine, rifampicin, or St John’s Wort)
  • changes smoking status (tobacco can lower plasma levels of theophylline)

Alcohol at risk patients

High alcohol intake can reduce plasma theophylline


  • Periodically
    • Full blood count
    • Serum potassium

Potassium at risk patients

Potassium at risk patients includes those:

  • taking concomitant beta-2 agonists, corticosteroids, or diuretics
  • with severe asthma


Effects of enzyme inhibiting or enzyme inducing drugs

Enzyme inhibiting or inducing drugs can affect plasma theophylline levels significantly. Check levels where necessary.

Effects of pregnancy

During pregnancy protein binding decreases; the free level of drug will increase; and so a lower therapeutic range may be appropriate. Consider checking levels frequently, in particular in pregnant women with acute severe asthma or who are critically dependent on therapeutic theophylline.

Brand prescribing and dispensing

The rate of absorption from modified-release preparations can vary between brands. Patients should therefore be maintained on the same brand.


Enquiries about this page

Contact us if you have any enquiries about the drug monitoring information on this page.