indication

For the termination of pregnancy during the second trimester (from the 12th through the 20th gestational week as calculated from the first day of the last normal menstrual period), as well as for evacuation of the uterine contents in the management of missed abortion or intrauterine fetal death up to 28 weeks of gestational age as calculated from the first day of the last normal menstrual period. Also used in the management of nonmetastatic gestational trophoblastic disease (benign hydatidiform mole). Other indications include improving the cervical inducibility (cervical "ripening") in pregnant women at or near term with a medical or obstetrical need for labor induction, and the management of postpartum hemorrhage.

pharmacology

Dinoprostone is equivalent to prostaglandin E2 (PGE2). It stimulates labor and delivery by stimulating the uterine, and thus terminates pregnancy. Dinoprostone is also capable of stimulating the smooth muscle of the gastrointestinal tract of man. This activity may be responsible for the vomiting and/or diarrhea that is not uncommon when dinoprostone is used to terminate pregnancy.

mechanism of action

Dinoprostone administered intravaginally stimulates the myometrium of the gravid uterus to contract in a manner that is similar to the contractions seen in the term uterus during labor, resulting in the evacuation of the products of conception from the uterus. It is believed that dinoprostone exerts its uterine effects via direct myometrial stimulation, but the exact mechanism of action is unkown. Other suggested mechanisms include the regulation of cellular membrane calcium transport and of intracellular concentrations of cyclic 3',5'-adenosine monophosphate. Dinoprostone also appears to produce local cervical effects including softening, effacement, and dilation. The exact mechanism of action for this effect is also unknown, but it has been suggested that this effect may be associated with collagen degradation caused by secretion of the enzyme collagenase as a partial response to locally administered dinoprostone.

toxicity

Oral, mouse: LD₅₀ = 750 mg/kg; Oral, rat: LD₅₀ = 500 mg/kg.

biotransformation

Rapid metabolism of dinoprostone occurs primarily in the local tissues; any systemic absorption of the medication is cleared mainly in the maternal lungs and, secondarily, at sites such as the liver and kidneys.

absorption

Absorbed at a rate of 0.3 mg per hour over 12 hours while the vaginal system is in place.

half life

Less than 5 minutes.

route of elimination

The major route of elimination of the products of PGE2 metabolism is the kidneys.