Progesterone and is responsible for approximately 70% of cytochrome P450-mediated progesterone metabolism. Other routes include 6α-, 16α-, and 16β-hydroxylation. However, treatment of women with ketoconazole, a strong CYP3A4 inhibitor, had minimal effects on progesterone levels, producing only a slight and non-significant increase, and this suggests that cytochrome P450 enzymes play only a small role in progesterone metabolism. In women, progesterone levels are relatively low during the preovulatory phase of the menstrual cycle, rise after ovulation, and are elevated during the luteal phase, as shown in diagram below. Progesterone levels tend to be less than 2 ng/mL prior to ovulation, and greater
Pharmacokinetics of progesterone of the menstrual cycle with LC–MS/MS are 6.7 to 22.2 ng/mL. When the unreliable method of standalone RIA has been used to measure progesterone levels with oral progesterone, far higher peak levels of 6.5 to 10.2 ng/mL, 13.8 to 19.9 ng/mL, and 32.3 to 49.8 ng/mL have been erroneously observed after single 100, 200, and 300 mg doses, respectively. In addition, progesterone levels have been inaccurately measured by RIA as remaining elevated for 12 to 24 hours. Regardless of assay method, peak levels of progesterone following a dose of oral progesterone occur after about 1 to 3 hours. The elimination