<p><strong>Oral micronized capsules</strong></p><p>Following oral administration of progesterone in the micronized soft-gelatin capsule formulation, peak serum concentration was achieved in the first 3 hours. The absolute bioavailability of micronized progesterone is unknown at this time. In postmenopausal women, serum progesterone concentration increased in a dose-proportional and linear fashion after multiple doses of progesterone capsules, ranging from 100 mg/day to 300 mg/day <sup class="text-reference-group"><a class="reference-popover-link" data-content="Official drug label" href="#label-reference">Label</a></sup>. </p><p><strong>IM administration</strong></p><p>After intramuscular (IM) administration of 10 mg of progesterone in oil, the maximum plasma concentrations were achieved in about 8 hours post-injection and plasma concentrations stayed above baseline for approximately 24 hours post-injection. Injections of 10, 25, and 50 mg lead to geometric mean values for maximum plasma concentration (CMAX) of 7, 28, and 50 ng/mL, respectively <sup class="text-reference-group"><a class="reference-popover-link" data-content="PROGESTERONE INJECTION USP IN SESAME OIL FOR INTRAMUSCULAR USE ONLY" href="#reference-F3916">25</a></sup>. Progesterone administered by the intramuscular (IM) route avoids significant first-pass hepatic metabolism. As a result, endometrial tissue concentrations of progesterone achieved with IM administration are higher when compared with oral administration. Despite this, the highest concentrations of progesterone in endometrial tissue are reached with vaginal administration <sup class="text-reference-group"><a class="reference-popover-link" data-content="Paulson RJ, Collins MG, Yankov VI: Progesterone pharmacokinetics and pharmacodynamics with 3 dosages and 2 regimens of an effervescent micronized progesterone vaginal insert. J Clin Endocrinol Metab. 2014 Nov;99(11):4241-9. doi: 10.1210/jc.2013-3937. Epub 2014 Feb 25. (PubMed ID 24606090)" href="#reference-A175657">11</a></sup>. </p><p><strong>Note on oral contraceptive tablet absorption</strong></p><p>Serum progestin levels peak about 2 hours after oral administration of progesterone-only contraceptive tablets, followed by rapid distribution and elimination. By 24 hours after drug administration, serum levels remain near the baseline, making efficacy dependent upon strict adherence to the dosing schedule. Large variations in serum progesterone levels occur among individuals. Progestin-only administration leads to lower steady-state serum progestin levels and a shorter elimination half-life than concurrent administration with estrogens <sup class="text-reference-group"><a class="reference-popover-link" data-content="Norethindrone FDA label" href="#reference-F3904">22</a></sup>. </p>