Kinetic alteration of theophylline at therapeutic doses

To report a case of a patient diagnosed as having bronchial asthma treated with intravenous infusion of theophylline, who presented an episode of altered theophylline metabolism with a disproportionately increase in serum concentrations together with tachycardia and symptoms of intoxication.

A 51-year-old white woman with a history of bronchial asthma was treated with intravenous infusion of theophylline in an Intensive Care Unit. Bayesian pharmacokinetic approach for dose individualization was done and linear kinetics of theophylline were observed. At therapeutic dose, an alteration of theophylline metabolism had happened, that induced a decrease on the theophylline clearance coinciding with an increase of dose. The serum concentration at this dose was 23.9 microg/ml and this was associated with symptoms compatible with intoxication by theophylline. All factors that could change theophylline elimination were analyzed. A possible drug interaction, hypothyroidism and cardiac failure were ruled out. Clinical hepatic insufficiency was not determined, but an increase of hepatic enzymes was observed. Theophylline infusion was suspended during 5 hours, the serum levels returned to therapeutic values and hepatic enzymes returned to their initial values.

Episodes of anormal theophylline kinetics may occur, even with doses and serum concentrations considered to be therapeutic, especially in critically ill patients or those whose physical condition has deteriorated. This makes it necessary to carry out therapeutic drug monitoring of theophylline in this group of the population.