Considerations before switching
Incorrect switching could lead to subtherapeutic treatment or toxicity. Consider the following before switching between oral theophylline and intravenous (IV) aminophylline preparations.
Narrow therapeutic index
- Theophylline has a narrow therapeutic index, see our article on the management of medication that have a narrow therapeutic index for further information.
- Refer to your local guidelines for the therapeutic theophylline range to use.
- Aminophylline is a stable mixture of theophylline and ethylenediamine.
- Individuals with heart failure, liver impairment and viral infections may have a theophylline level higher than the upper limit.
- Individuals who smoke or drink alcohol may have a theophylline level which is less than the lower limit.
Salt factor
- The salt factor for aminophylline is approximately 0.8.
- Aminophylline contains 80% theophylline.
- The salt factor is required to calculate the daily dose of oral theophylline.
Calculation assumptions
- The calculation is for converting from IV aminophylline to oral theophylline.
- It assumes that the individual has been stable on IV aminophylline for at least 48 hours (reaching steady state levels) before starting oral theophylline.
- The dose of IV aminophylline is calculated using actual body weight or ideal body weight for obese individuals.
Interactions
- Review the individual’s full medication list for interactions with theophylline and aminophylline, including any over the counter medicines.
Introducing a new medication to the patients’ regimen during a switch could affect their theophylline levels. Check the product literature for the newly introduced medicine to identify any interaction risks with theophylline or aminophylline.
Oral theophylline to IV aminophylline
IV aminophylline may be required for individuals already taking oral theophylline in an acute emergency setting:
People on regular oral theophylline tablets do not usually need a loading dose of IV aminophylline.
Worked Example
For a 45 year old man who weighs 70kg, the maintenance dose of IV aminophylline is calculated using the following equation: 0.5mg/kg/hour.
A suitable IV aminophylline dose for this patient would be 35mg/hour.
IV aminophylline to oral theophylline
Considerations before switching
Before switching from IV aminophylline to oral theophylline:
- Ensure the individual is stable on IV aminophylline for at least 48 hours (reaching steady state levels) before starting oral theophylline.
- Check that the prescribed IV aminophylline dose is correct by completing an appropriate second check. Understanding when a check adds value to medication processes helps to identify the value of a second check.
- Consider factors that affect theophylline clearance, such as other medications, smoking and heart failure.
Worked example
A 45-year-old man is being given IV aminophylline at a rate of 35mg/hr. The method of calculating the oral theophylline dose is as follows:
- 35mg/hr x 24hrs = 840mg daily dose of IV aminophylline
- 840mg x 0.8 = 672mg of oral theophylline daily
- 672mg ÷ 2 = 336mg oral theophylline to give twice a day
A suitable regimen for this individual could be 300mg oral theophylline in the morning and 400mg in the evening.
Monitoring after the switch
Monitor plasma theophylline levels for individuals switched between oral theophylline and IV aminophylline.
Assess the individual for signs of toxicity and consider any additional monitoring on case-by-case basis.
Further information is available in our guidance on theophylline monitoring.
Update history
- Full review and update complete. Minor changes to structure and section on interactions added.
- Published