THEOPHYLLINE DOES NOT INCREASE VENTILATORY RESPONSES TO HYPERCAPNIA OR HYPOXIA

Theophylline is commonly believed to stimulate central respiratory centers. We studied the effect of oral theophylline therapy on ventilatory responses to hypercapnia and hypoxia during a double-blind placebo-controlled trial with a slow release oral theophylline preparation. We measured hypercapnic and hypoxic ventilatory responses using rebreathing techniques in 15 subjects (21 to 41 yr of age, with normal lung function) on three occasions: baseline, after 4 days of Drug 1, and after 4 days of Drug 2. For subjects receiving theophylline, the mean serum theophylline level was 11.3 + 1.3 (SE) mug/ml (range, 5.3 to 22.1). Unpleasant side effects were reported by 11 of the 15 subjects (nausea, jitteriness, and agitation) while receiving theophylline but not while receiving placebo. The mean hypercapnic ventilatory response with placebo was 4.3 +/- 0.9 L/min/mm Hg PA(CO2) and with theophylline it was 4.5 +/- 0.7 L/min/mm Hg PA(CO2). The mean hypoxic ventilatory response with placebo was -3.9 +/- 1.0 L/min/%Sa(O2) and with theophylline It was -2.7 +/- 0.4 L/min/%Sa(O2). Hypoxic responses for each subject were measured at similar Pv(CO2)BAR. There were no significant changes in ventilatory responses with theophylline. We conclude that theophylline use, at a dose sufficient to cause side effects, does not affect chemoreceptor responsiveness.