Background and objective: A single dose of theophylline improves hypoglycemia unawareness in type 1 diabetic patients. Prolonged theophylline use is, however, associated with emergence of tolerance. This study investigated whether prolonged use of theophylline retains efficacy for counterregulatory defects in patients with type 1 diabetes and hypoglycemia unawareness.
Methods: Experiments were performed with 12 subjects with type 1 diabetes and hypoglycemia unawareness. All subjects participated in a crossover study of 2 randomly scheduled 15-day study periods during which 250 mg theophylline twice daily or matching placebo was used. On the final day of each period, hyperinsulinemic (360 pmol x m(-2) x min(-1)) hypoglycemic (5.0, 3.5, 2.5 mmol x L(-1)) glucose clamps were used to assess counterregulatory and cardiovascular responses.
Results: Under normoglycemic conditions, there were no differences between theophylline and placebo. Under hypoglycemic conditions, theophylline enhanced responses of growth hormone, symptoms, heart rate, and pulse pressure (all P <.05), induced sweating at higher plasma glucose levels (P =.039), and reduced exogenous glucose requirements (P =.018). Hypoglycemia-induced responses of epinephrine, norepinephrine, and cortisol were not enhanced by theophylline.
Conclusions: Prolonged use of theophylline has a sustained effect on cardiovascular, metabolic, and symptom responses to hypoglycemia in patients with type 1 diabetes and hypoglycemia unawareness. Whether these results translate into clinical benefit remains to be determined.