Aminophylline is a xanthine which is most often used it the treatment of severe acute asthma.
Salt factor
- salt factor for aminophylline is approximately 0.8 (1)
- aminophylline contains 80% theophylline
- salt factor is required to calculate the daily dose of oral theophylline
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
- dose of IV aminophylline is calculated using actual body weight or ideal body weight for obese individual
Take base theophylline levels
- ideally take a plasma theophylline level 4 to 6 hours after the last known dose of oral theophylline
- take this level before starting the maintenance dose of IV aminophylline
- you do not need to wait for the results of the theophylline level to begin the maintenance infusion
- where the sampling hours fall outside 4 to 6 hours post oral theophylline dose, please liaise with a respiratory consultant
- refer to local policy and specialist teams for interpreting the levels
Start the maintenance infusion
- start the maintenance dose of intravenous aminophylline as per your local policy or the product literature
- you may need to adjust the maintenance dose of IV aminophylline to ensure the theophylline levels are within your local therapeutic rangedose of IV aminophylline is calculated using actual body weight, or ideal body weight for obese individuals
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 (1)
- a suitable IV aminophylline dose for this patient would be 35mg/hour
Side effects of aminophylline include:
- abdominal pain, nausea, headache, tremor, insomnia and palpitations, convulsions and cardiac arrhythmias.
Various drugs affect the half-life of theophylline:
- increased half-life is seen in heart failure, cirrhosis, viral infections, and drugs e.g. erythromycin, ciprofloxacin, cimetidine.
- decreased half-life is seen in heavy drinkers, smokers, and by drugs e.g. barbiturates, phenytoin, carbamazepine, rifampicin.
Check summary of product characteristics before prescribing this drug.
Reference:
- NHS Specialist Pharmacy Service (July 2025). Switching between aminophylline and theophylline in adults