Unaltered Drug Metabolizing Enzyme Systems in Type II Diabetes Mellitus Before and During Glyburide Therapy

Diabetes mellitus is associated with alterations in hepatic drug metabolizing enzyme activities in experimental animals. To determine whether Type II diabetes or glyburide affect hepatic drug metabolism, the authors used ¹³C‐labeled aminopyrine and caffeine breath tests as in vivo probes of the hepatic cytochrome P450 and P₁450 enzyme activities respectively in six subjects with Type II diabetes (4 women, 2 men). These subjects had been treated previously with diet, had an age range of 41–63 years, had a body mass index range of 24.1–43.3 kg/m² and had a mean fasting plasma glucose of 14.6 ± 1.2 mM and a mean hemoglobin A_1c of 12.2 ± 0.7%. These subjects did not drink alcohol or take drugs known to affect hepatic drug metabolism. The caffeine and aminopyrine breath tests (CBT, ABT) were performed sequentially while fasting before the start of glyburide treatment (5 mg daily) and at weekly intervals for 4 weeks. ABT and CBT values are expressed as cumulative percentage of dose exhaled through 2 hours. Before beginning glyburide, the mean ABT and CBT results were 10.2 ± 0.7% and 4.2 ± 0.7% respectively, well within the normal ranges for these tests (ABT 6.5–15%; CBT 2.5–10%). The ABT and CBT values remained unaltered during 4 weeks of glyburide therapy. However, FBS decreased to 10.2 ± 1.1 mM and HbA₁C to 10.1 ± 0.8% by the end of drug treatment. Type II diabetes that is poorly controlled by diet alone is not associated with alterations of the hepatic drug metabolizing enzymes as judged by the caffeine and aminopyrine breath tests. Furthermore, glyburide does not induce or inhibit the drug metabolizing enzyme systems in the liver, thereby precluding drug‐drug interactions of this type. 1990 American College of Clinical Pharmacology