Switching between aminophylline and theophylline in adult respiratory care

Amisha Gopal, Regional Medicines Information Pharmacist, London Medicines Information Service Published

Intravenous aminophylline is used acutely for emergency respiratory conditions and we give a stepped approach on how to switch to oral theophylline

Considerations before switching

The following points should be taken into account before switching between preparations.

Narrow therapeutic drug

  • Theophylline is a narrow therapeutic drug.
  • Aminophylline is a stable mixture of theophylline and ethylenediamine.
  • Incorrect switching could lead to toxicity.

Salt equivalence/salt factor

  • The salt factor for aminophylline is approximately 0.8. This means the amount of aminophylline which is theophylline is about 80%.
  • You will need the salt factor to calculate the nearest equivalent daily dose of oral theophylline.

Calculation assumptions

  • The individual is stable on intravenous aminophylline for at least 48 hours (reaching steady state levels) before starting oral theophylline.
  • The prescribed dose of intravenous aminophylline is correct and the healthcare professional has taken into account factors affecting theophylline clearance (for example: medicine interactions, smoking status and congestive heart failure).

Switching from intravenous aminophylline to oral theophylline

Worked example

A 45-year-old man is being given intravenous 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 intravenous 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.

Switching from oral theophylline to intravenous aminophylline

Intravenous aminophylline may be required for individuals already taking oral theophylline in an acute emergency setting:

  • People on regular oral theophylline tablets usually do not need a loading dose of intravenous aminophylline.
  • In severe cases of reversible airways obstruction, liaise with a respiratory consultant.

Monitoring after the switch

Monitor plasma theophylline levels for individuals switched from intravenous aminophylline to oral theophylline.

The healthcare professional initiating the switch should assess the patient and consider any additional monitoring on case-by-case basis.

Further SPS information is available on theophylline monitoring.