From the Guidelines
The half-life of progesterone injections, specifically 17-alpha-hydroxy-progesterone caproate (17P), is approximately 22 to 38 hours, allowing for weekly intramuscular injections of 250 mg to maintain therapeutic levels in the prevention of preterm birth in women with a history of spontaneous preterm birth. The formulation of 17P creates a depot effect, enabling slower absorption and a longer duration of action compared to oral progesterone, which is crucial for maintaining consistent hormone levels in conditions like preterm birth prevention 1. The dosing regimen of 17P, as recommended by the Society for Maternal-Fetal Medicine, involves weekly intramuscular injections of 250 mg starting at 16-20 weeks of gestation until 36 weeks of gestation or delivery, specifically for women with a singleton gestation and a history of prior spontaneous preterm birth between 20 and 36 6/7 weeks of gestation 1. Key points to consider include:
- The specific formulation and dosing regimen of 17P are critical for its effectiveness in preventing preterm birth.
- The use of 17P is recommended for women with a singleton gestation and a history of prior spontaneous preterm birth, but not for multiple gestations or other conditions where its effectiveness has not been established 1.
- Patients should be aware of potential side effects, such as injection site soreness, and rotating injection sites can help minimize discomfort.
- The relatively long half-life of injectable 17P makes it an effective option for maintaining consistent hormone levels when oral administration is not preferred or effective.
From the FDA Drug Label
CLINICAL PHARMACOLOGY: ... Pharmacokinetics and Metabolism Absorption After intramuscular administration of 10 mg of progesterone in oil maximum plasma concentrations (geometric mean of 7 ng/mL) were reached within approximately 8 hours after injection and plasma concentrations remained above baseline for about 24 hours after injection
The mean plasma metabolic clearance rate in cycling women is 2510 ± 135 (SEM) L/day
The half-life of progesterone injection is not directly stated in the drug label. However, it is mentioned that plasma concentrations remained above baseline for about 24 hours after injection.
- The pharmacokinetic data was determined in a small number of patients, limiting the precision in which population values may be estimated 2. Based on the information provided, no conclusion can be drawn about the exact half-life of progesterone injection.
From the Research
Progesterone Half-Life Injection
- The half-life of progesterone injections is not explicitly stated in the provided studies. However, the pharmacokinetics of progesterone formulations are discussed in several studies 3, 4, 5.
- A study comparing the bioavailability of subcutaneous and intramuscular progesterone formulations found that the subcutaneous formulation had a higher exposure and peak concentration than the intramuscular formulation 4.
- Another study found that a novel aqueous progesterone formulation administered subcutaneously had a faster absorption rate and reached peak serum levels earlier than an intramuscular reference formulation 5.
- The studies suggest that the pharmacokinetics of progesterone formulations can vary depending on the route of administration and the specific formulation used 4, 5.
- However, the half-life of progesterone injections is not directly addressed in the provided studies, and further research would be needed to determine this information.
Routes of Administration
- Progesterone can be administered through various routes, including oral, intramuscular, sublingual, and intravaginal 3.
- The intravaginal route is considered effective with fewer side effects, and several formulations are available, including vaginal gels and tablets 3, 6.
- Subcutaneous administration of progesterone is also being explored as a potential alternative to existing treatments 4, 5.