Description and Composition

Prometrium is a brand name for progesterone, which is a naturally occurring female hormone. Each Prometrium capsule contains a micronized form of progesterone. It is available in 100 mg and 200 mg dosages. The inactive ingredients include peanut oil, gelatin, glycerin, lecithin, and titanium dioxide.

Indications for Use

Prometrium is prescribed for hormone replacement therapy in postmenopausal women who have an intact uterus. It is also used to treat secondary amenorrhea, which is the absence of menstrual cycles in women who previously had regular periods. Additionally, it can assist in preventing endometrial hyperplasia in non-hysterectomized women receiving estrogen therapy.

Administration Instructions

Prometrium is administered orally. The typical dosage for hormone replacement therapy is 200 mg per day at bedtime for 12 consecutive days of a 28-day cycle. For secondary amenorrhea, the dosage is generally 400 mg at bedtime for 10 days. Capsules should be swallowed whole with water, and should not be crushed or chewed.

Mechanism of Action

Progesterone in Prometrium acts on progesterone receptors in the endometrial tissue. This influences the transcription and translation of target genes, helping to produce a secretory endometrium that is conducive to the successful implantation of an embryo. It also suppresses the pituitary release of gonadotropins, which in turn inhibits the LH surge essential for ovulation.

Pharmacokinetics Overview

When administered orally, progesterone is rapidly absorbed in the gastrointestinal tract. Peak plasma concentrations are achieved within 1 to 3 hours. The bioavailability of Prometrium increases when taken with food. Progesterone is extensively metabolized in the liver and its metabolites are excreted mainly in urine, predominantly as glucuronide conjugates.

Dosage Adjustments

The dosage of Prometrium may need to be adjusted based on clinical response or side effect profile. Patients with hepatic impairment should exercise caution and may require a dosage reduction. Elderly patients may also need dosage adjustments due to the increased likelihood of co-morbid conditions or concomitant medications.

Drug Interactions

Prometrium may interact with drugs that induce liver enzymes, such as rifampin or carbamazepine, potentially reducing its effectiveness. Concomitant use with cytochrome P450 inhibitors like ketoconazole may increase progesterone levels. Caution should be exercised when using other hormone therapies concurrently.

Adverse Effects Profile

Common side effects of Prometrium may include dizziness, headache, abdominal pain, and breast tenderness. Serious adverse effects, though rare, include thromboembolic disorders, retinal vascular lesions, and liver dysfunction. Patients should be monitored for any signs of fluid retention, depression, and jaundice.

Special Populations

Prometrium is not indicated for use in pediatric patients. In pregnant women, progesterone must be used only if clearly needed, and it falls under Pregnancy Category B. Lactating mothers should exercise caution, as progesterone is excreted in breast milk. Renal impairment does not significantly affect progesterone pharmacokinetics.

Storage and Handling

Prometrium capsules should be stored at room temperature, away from moisture and light. The original packaging should be used to protect the capsules from excessive heat and humidity. Do not store this medication in the bathroom, and keep it out of reach of children.

Clinical Monitoring

Regular follow-up appointments are necessary to monitor the patient’s response to Prometrium therapy. Blood pressure, liver function tests, and blood glucose levels should be assessed periodically. Any new or worsening symptoms should be promptly reported to a healthcare provider.

Mechanisms of Metabolism

Progesterone undergoes extensive hepatic metabolism primarily via hydroxylation by cytochrome P450 enzymes. Metabolites such as pregnanediols and pregnanolones are subsequently conjugated and excreted in urine. Progesterone also forms serum-binding proteins like corticosteroid-binding globulin and albumin.

Contraindications to Use

Prometrium is contraindicated in patients with known hypersensitivity to progesterone or any component of the product. It should not be used in individuals with peanut allergies due to the presence of peanut oil. Other contraindications include undiagnosed vaginal bleeding, active or suspected malignancy of the breast or genital organs, and a history of thrombophlebitis or thromboembolic disorders.

Clinical Studies

Clinical trials have demonstrated the efficacy of Prometrium in preventing endometrial hyperplasia and inducing withdrawal bleeding in amenorrhoeic women. Studies also support its role in hormone replacement therapy, highlighting improved symptom control and patient satisfaction relative to placebo.