Theophylline is metabolised by cytochrome P450 in the liver, principally by CYP1A2. Many drugs interact with
theophylline by inhibition or potentiation of its metabol- ism.
Theophylline has a narrow therapeutic range, and small increases in
serum levels can result in
toxicity. Moreover,
symptoms of serious
toxicity such as convulsions and arrhythmias can occur before minor
symptoms suggestive of
toxicity. Furthermore, age, cigarette smoking, chronic obstructive airways disease, congestive heart failure, and liver disease (cirrhosis, acute
hepatitis) can also affect
theophylline clearance. Within the context of interactions, aminophylline is expected to behave like
theophylline, because it is a complex of
theophylline with ethylenediamine.