A review of conventional and sustained-release formulations of oral natural micronized progesterone in obstetric indications.

BACKGROUND: Exogenous progesterone is a treatment option for obstetric indications associated with reduced progesterone activity. Oral natural micronized progesterone (NMP) is effective, although it requires multiple daily doses and may cause adverse events due to its active metabolites. A sustained-release formulation of NMP (NMP-SR) has been developed to overcome the limitations of conventional oral NMP. METHODS: This narrative review examines the available evidence for oral NMP and NMP-SR in several obstetric indications of interest. RESULTS: Literature searches identified 17 studies of oral NMP (luteal phase support during assisted reproduction, prevention of threatened miscarriage, prevention of preterm delivery), and clinical studies supporting use of NMP-SR (luteal phase support during intrauterine insemination, maintenance of high-risk pregnancy). Oral NMP was effective for luteal phase support during in vitro fertilization and intrauterine insemination, prevention of threatened miscarriage, and prevention of preterm delivery. NMP-SR was comparable to dydrogesterone for luteal phase support during intrauterine insemination and effectively maintained high-risk pregnancies. Oral NMP-SR was well tolerated. CONCLUSIONS: By releasing progesterone gradually and circumventing first-pass metabolism, NMP-SR elicits the desired therapeutic effect with benefits over conventional oral NMP in terms of bioavailability, once-daily dosing and improved tolerability. Oral NMP-SR appears to be a valuable option for treating obstetric conditions associated with insufficient progesterone exposure.