Effect of the ethinylestradiol/levonorgestrel combined oral contraceptive on the activity of cytochrome P4503A in obese women

AIM(S) While it is known that CYP3A4/5 activity is decreased with combined oral contraceptive (COC) use and obesity suppresses CYP expression, the combined effects of obesity and COC use on CYP3A4/5 activity are unclear. Therefore, our aim was to examine the effect of COC usage on CYP3A4/5 activity in obese women. METHODS Thirty-four, obese (body mass index, BMI > 30kgm^-2) women of reproductive age (18-35years old) were placed on a COC pill containing 20μg ethinylestradiol/100μg levonorgestrel for 21days starting at the onset of menses. A midazolam pharmacokinetic study was conducted prior to initiation and after 21days of COC treatment. Serial blood samples were collected and plasma concentrations of midazolam were measured using liquid chromatography tandem mass spectrometry. Pharmacokinetic parameters were estimated using a non-compartmental method. RESULTS Midazolam clearance, a surrogate measure of CYP3A4/5 activity, was significantly decreased upon COC use (63.3lh^-1vs. 53.9lh^-1, P < 0.05). A median decrease of 5.6lh^-1 (95% CI -4.1, 13.3lh^-1) was observed. However, the magnitude of change was similar to that reported in women with normal BMI. CONCLUSIONS Although we hypothesized that obesity might amplify the impact on CYP3A4/5 activity in COC users, we found that this was not the case. This finding is reassuring regarding potential additional drug-drug interactions in obese COC users as CYP3A4/5 is a major enzyme in the metabolism of many marketed drugs.