BACKGROUND: Makena (17-hydroxyprogesterone caproate) was approved by the United States Food and Drug Administration for the prevention of recurrent spontaneous preterm birth in 2011 under the accelerated approval pathway, but fundamental pharmacokinetic or pharmacodynamic (Phase 1 and Phase 2) studies were not performed. At the time, there were no dose-response or concentration-response data. The therapeutic concentration was not known. The lack of such data brings into question the dosing regimen for 17-hydroxyprogesterone caproate and if it was optimized.
OBJECTIVE: The purpose of this study was to evaluate the dosing regimen for 17-hydroxyprogesterone by analyzing 3 data sets in which the 17-hydroxyprogesterone caproate pharmacology was evaluated, namely the Maternal-Fetal Medicine Omega 3 study, the Obstetric-Fetal Pharmacology Research Units study, and the Obstetrical-Fetal Pharmacology Research Centers study. If an inappropriate dosing regimen could be identified, such information could inform future studies of pharmacotherapy in pregnancy.
METHODS: Data from the Omega 3 study were used to determine if plasma concentration was related to spontaneous preterm birth risk and if a threshold concentration could be identified. Data from the Obstetric-Fetal Pharmacology Research Units study were used to determine the half-life of 17-hydroxyprogesterone caproate and to develop a model to simulate drug concentrations with various dosing regimens. Data from the Obstetrical-Fetal Pharmacology Research Centers study were used to determine the relationship between dose and safety outcomes.
RESULTS: Analysis of the Omega 3 data set indicated that the risk for spontaneous preterm birth decreased as the log concentration of 17-hydroxyprogesterone caproate increased (odds ratio, 0.04; 95% confidence interval, 0.00-0.90). A steady state concentration of >9 ng/mL (equivalent to >8 ng/mL at 25-28 weeks) was associated with the lowest risk for spontaneous preterm birth (hazard ratio, 0.52; 95% confidence interval, 0.27-0.98; P=.04); this concentration was not achieved in 25% of subjects who received the 250 mg weekly dose. In the Obstetrical-Fetal Pharmacology Research Units study, the adjusted half-life (median and interquartile range) of 17-hydroxyprogesterone caproate was 14.0 (11.5-17.2) days. Simulations indicated that with the 250 mg weekly dose, >5 weekly injections were required to reach the 9 ng/mL target; however, those with the shortest half-life (corresponding to higher clearance), never reached the targeted 9 ng/mL concentration. In 75% of subjects, a loading dose of 500 mg weekly for 2 weeks followed by 250 mg weekly achieved and maintained the 9 ng/mL concentration within 2 weeks but in those 25% with the shortest half-life, concentrations exceeded the 9 ng/mL target for only 3 weeks. In the Obstetrical-Fetal Pharmacology Research Centers study, all 65 subjects who received a weekly dose of 500 mg exceeded the 9 ng/mL steady state.
CONCLUSIONS: The dosing regimen for 17-hydroxyprogesterone caproate was inadequate. There is a significant inverse relationship between drug concentration and spontaneous preterm birth. The risk was lowest when the concentration exceeded 9 ng/mL, but 25% of women who received the 250 mg weekly dose never reached or maintained this concentration. The drug\'s long half-life necessitates a loading dose to achieve therapeutic concentrations rapidly. The omission of basic pharmacologic studies to determine the proper dosing may have compromised the effectiveness of 17-hydroxyprogesterone caproate. Future pharmacotherapy trials in pregnancy must first complete fundamental pharmacology studies.

The effectiveness of 17-hydroxyprogesterone caproate is unclear as trials have provided conflicting results. With the absence of fundamental pharmacologic studies addressing dosing or the relationship between drug concentration and gestational age at delivery, the effectiveness of the medication cannot be evaluated.
This study aimed to evaluate the relationship between plasma concentrations of 17-hydroxyprogesterone caproate and preterm birth rates and gestational age at preterm delivery and to assess the safety of the 500-mg dose.
This study recruited 2 cohorts with previous spontaneous preterm birth; 1 cohort (n=143) was randomly assigned to either 250-mg or 500-mg 17-hydroxyprogesterone caproate, and the other cohort (n=16) was receiving the 250-mg dose for routine care. Steady-state trough plasma concentrations of 17-hydroxyprogesterone caproate obtained at 26 to 30 weeks of gestation were correlated to dose, spontaneous preterm birth rates, and measures of gestational length. Furthermore, maternal and neonatal safety outcomes were evaluated according to dose.
There was a dose proportional increase in trough plasma concentrations with the 250-mg (median, 8.6 ng/m; n=66) and 500-mg (median, 16.2 ng/mL; n=55) doses. In 116 compliant participants with blood samples, drug concentration was not related to the spontaneous preterm birth rate (odds ratio, 1.00; 95% confidence interval, 0.93-1.08). However, there was a significant relationship between drug concentration and both the interval from the first administration to delivery (interval A: coefficient, 1.11; 95% confidence interval, 0.00-2.23; P=.05) and the interval from the 26- to 30-week blood draw to delivery (interval B: coefficient, 1.56; 95% confidence interval, 0.25-2.87; P=.02). The spontaneous preterm birth rate or measures of gestational length were not related to dose. Postenrollment cerclage adversely affected all pharmacodynamic assessments because it was a powerful predictor of spontaneous preterm birth (odds ratio, 4.03; 95% confidence interval, 1.24-13.19; P=.021) and both measures of gestational length (interval A [coefficient, -14.9; 95% confidence interval, -26.3 to -3.4; P=.011] and interval B [coefficient, -15.9; 95% confidence interval, -25.8 to -5.9; P=.002]). Initial cervical length was significantly related to the risk of postenrollment cerclage (odds ratio, 0.80; 95% confidence interval, 0.70-0.92; P=.001). Maternal and neonatal safety outcomes were similar in both dosing groups.
In this pharmacodynamic study, trough plasma 17-hydroxyprogesterone caproate concentrations were significantly associated with gestational age at preterm birth but not with the preterm birth rate. Postenrollment cerclage was a powerful predictor of spontaneous preterm birth rate and gestational length. Initial cervical length predicted the risk of postenrollment cerclage. Adverse events were similar with the 500-mg and 250-mg doses of 17-hydroxyprogesterone caproate.

Obstetrical healthcare providers frequently field questions about the safety of medications recommended or prescribed to their pregnant patients. Most women use as least 1 medication during pregnancy; however, there is little information about the safety or appropriate dosing of many medications during this phase of life. In addition, the development of drugs for use in pregnant women trails behind the development of drugs intended for other sectors of the population. Our goal is to inform the obstetrics community about the US Food and Drug Administration authority and their role in approving drugs for marketing. We begin with the statutes that led to the creation of the Food and Drug Administration and its current organization. We then cover drug development and the Food and Drug Administration review process, including the role of the advisory committee. The different types of drug approvals are discussed, with some specific examples. Finally, we enumerate the drugs specifically approved for use in obstetrics and contrast them with drugs commonly used by pregnant women and drugs used \"off-label\" during pregnancy. The Food and Drug Administration is committed to protecting and advancing the public health of pregnant women by guiding the development and ensuring the availability of effective and safe therapeutics for obstetrical indications and for medical conditions during pregnancy. We hope this review will inspire more research addressing drug use during pregnancy.

Progesterone has been used for preventing preterm birth with mixed results. The American College of Obstetricians and Gynecologists and Society for Maternal-Fetal Medicine recommended the use of 17-hydroxyprogesterone caproate for risk reduction of recurrent spontaneous preterm birth based on the results of a multicenter, randomized trial in the United States. However, recent literature lacks consensus for efficacy in the American population. In addition, partial adherence and outcomes thereof are underreported. Hence, the relationship between practical adherence to 17-hydroxyprogesterone caproate and outcomes were evaluated.
The objective of this study was to evaluate the adherence to 17-hydroxyprogesterone caproate, defined as receipt of greater than 80% of intended injections, at an outpatient maternal-fetal medicine center and its effect on maternal and neonatal outcomes.
This retrospective cohort study included women older than 18 years with a singleton gestation, history of spontaneous preterm birth who initiated 17-hydroxyprogesterone caproate weekly injections between 16 and 20 weeks\' gestational age and delivered between the years 2014 and 2017. Women receiving 17-hydroxyprogesterone caproate injections outside of the clinic were excluded. The primary outcome of adherence and secondary outcomes of gestational age at delivery, birthweight, and neonatal outcomes were analyzed using descriptive data, independent t-test, Mann-Whitney U test, chi-square test, and Fisher exact test, where appropriate, with a P value <.05 being considered significant.
Adherence to 17-hydroxyprogesterone caproate occurred in 38 of 92 (41.3%) women included in the study. At baseline, there was a difference in age between groups of adherent and nonadherent women (adherent: 30.8 years; nonadherent: 27.4 years; P=.002). The rate of spontaneous preterm birth less than 37, 35, and 32 weeks were not significantly different in those who were adherent vs nonadherent to 17-hydroxyprogesterone caproate. There were no differences in gestational age at delivery (adherent: 36.8±2.6 weeks; nonadherent: 36.5±3.8 weeks; P=.66), birthweight (adherent: 2776 g; nonadherent: 2709 g; P=.68), or composite neonatal morbidity (adherent: 18.4%; nonadherent: 20.4%; P=.86) between the adherent and nonadherent groups. Neonatal intensive care unit length of stay was 15.5 days in the adherent group compared with 15 days in the nonadherent group (P=.72).
Real-world adherence to 17-hydroxyprogesterone caproate is suboptimal with less than half of women adherent to in-clinic administration. Adherence to 17-hydroxyprogesterone caproate was not associated with a difference in gestational age at delivery or birthweight compared with nonadherence. Further studies are needed to assess the outpatient administration and benefit of 17-hydroxyprogesterone caproate therapy.

Preterm birth (PTB) is a multifactorial syndrome occurring before the 37th week of fullterm pregnancy [1]. Babies delivered preterm experience short-term and long-term complications affecting multiple organ systems, and serious maternal complications include hemorrhage and infection. Each year, an estimated 15 million babies are born preterm, and complications from prematurity are the leading cause of death among children up to 5 years of age [2]. With another increase in PTB rates over the last several years, the United States continues to have the highest incidence of any industrialized country [3]. Makena (a progesterone analog) is the only FDA approved medication available in the United States to reduce the risk of PTB. Its use is only indicated in women who are currently pregnant with one fetus and have unexpectedly delivered a baby preterm in the past [4]. Furthermore, Makena is very expensive and not used in mothers with multiple gestations or other risk factors, such as infection, preeclampsia and obesity. Consequently, physicians commonly prescribe supportive therapies, such as magnesium sulfate, to slow uterine contractions, and glucocorticoids to stimulate fetal lung maturity.
In this article, we review the full spectrum of in vivo models that investigators have developed to study PTB, including rodent, ruminant and non-human primate models. We evaluate the discrepancies among various models, the shortcomings of individual models and how well these models reflect various causes of PTB in humans.
Recent studies reveal that infection is unessential in reproductive disorders linked to inflammation, and that infection and inflammation are two of many triggers of PTB [1, 5-6]. Despite such findings, many investigators continue recycling infectious- (using bacterium) and non-infectious-based models (using products of bacteria or individual cytokines). These models are inconsistent across laboratories, and produce variable degrees of maternal morbidity (inconsistent with human PTB).
The aim of this review is to encourage the reproductive science community to rethink the design of non-infectious PTB animal studies. While these models have strengthened our understanding of the mediators and triggers of PTB, we must develop improved models that are more consistent with the various factors associated with human PTB (Fig. 1). If we continue viewing PTB through one lens or dimension, Makena will remain the only FDA approved medication. In vivo PTB research requires multi-model, multifactorial approaches that account for the complexity of living animals within and between species.

A systematic polymorph screening process was conducted on the steroid hydroxyprogesterone caproate, which had only one previously described orthorhombic crystalline form (A), in order to fully elucidate its solid state properties. Cooling, anti-solvent and evaporative techniques largely reproduced the same polymorph, but slurries in various solvents over two days produced a new triclinic form (B). Experiments at different temperatures in ethyl acetate or isopropyl alcohol confirmed this was an enantiotropic system with a transition temperature of approximately 30°C. DSC was used to confirm the transition of Form B to Form A below the melting point. Form B was the thermodynamically stable form at room temperature, and 8% less soluble in a non-aqueous solvent mixture. In viscous solvents used commercially to dissolve the oil-soluble steroid for injection, solutions near the solubility limit can remain supersaturated after exposure to cooler temperatures for months. In resolving the crystalline structure of Form A, a third conformational polymorph was detected that exists only at -133 to -143°C; this monoclinic form was designated Form C, and converts back to Form A upon warming to room temperature. These studies have increased the understanding of this drug and how the polymorphs may affect its physical stability in different dosage forms.