Description

Misoprostol is a synthetic analog of prostaglandinE1​ (PGE1​). The 1% HPMC (hydroxypropyl methylcellulose) dispersion is a specific formulation of misoprostol, where the active drug is dispersed in a polymer matrix. This formulation is often used to ensure stability and to control the release of the drug, particularly in vaginal or buccal tablet forms for obstetric and gynecological applications.

Indication

Misoprostol has a wide range of indications, primarily due to its effects on the uterine muscle and the gastrointestinal tract. The 1% HPMC dispersion formulation is most commonly used for gynecological indications, which include:

• Cervical Ripening and Labor Induction: To soften and dilate the cervix and to stimulate uterine contractions to initiate labor.

• Medical Abortion: In combination with other medications (e.g., mifepristone), to induce a complete abortion.

• Treatment and Prevention of Postpartum Hemorrhage: To prevent or treat excessive bleeding after childbirth.

In a different formulation, misoprostol is also indicated for:

• Prevention of NSAID-Induced Gastric Ulcers: To prevent gastric and duodenal ulcers caused by long-term use of non-steroidal anti-inflammatory drugs (NSAIDs).

• Treatment of Duodenal Ulcers: To promote the healing of duodenal ulcers.

Mechanism of Action

The mechanism of action of misoprostol is based on its ability to mimic the effects of the natural prostaglandinE1​. Its effects are localized to two main organ systems:

1. Uterine and Cervical Effects

• Binding to Prostaglandin Receptors: Misoprostol binds to and activates specific prostaglandin receptors (specifically,EP2​ andEP3​ subtypes) on the smooth muscle cells of the uterus (myometrium) and the cervix.

• Uterine Contractions: The activation of these receptors leads to an increase in intracellular calcium, which causes the myometrium to contract. These contractions are essential for the induction of labor and for expelling the contents of the uterus during a medical abortion or to control postpartum bleeding.
• Cervical Ripening: Misoprostol promotes the breakdown of collagen in the cervical tissue, leading to the softening, effacement, and dilation of the cervix. This process is known as cervical ripening.

2. Gastrointestinal Effects

• Inhibition of Gastric Acid Secretion: Misoprostol directly inhibits the secretion of gastric acid from the parietal cells in the stomach.

• Cytoprotection: It also enhances the production of protective factors in the stomach lining. It increases the secretion of mucus and bicarbonate, which form a protective barrier against gastric acid.

• Increased Mucosal Blood Flow: It is also believed to increase blood flow to the gastric mucosa, which aids in healing and protection.

The 1% HPMC dispersion is a formulation strategy to control the release of misoprostol, potentially leading to a more gradual and sustained effect, particularly when administered vaginally for labor induction or abortion.