Brand of dinoprostone vaginal insert
Rev. 5/06 Rx only
Dinoprostone vaginal insert is a thin, flat, polymeric slab which is rectangular in shape with rounded corners contained within the pouch of an off-white knitted polyester retrieval system. Each slab is buff colored, semitransparent and contains 10 mg of dinoprostone in a hydrogel insert. An integral part of the knitted polyester retrieval system is a long tape designed to aid retrieval at the end of the dosing interval or earlier if clinically indicated. The finished product is a controlled release formulation which has been found to release dinoprostone in vivo at a rate of approximately 0.3 mg/hr.
The chemical name for dinoprostone (commonly known as prostaglandin E2 or PGE2) is 11α, 15S-dihydroxy-9-oxo-prosta-5Z,13E-dien-1-oic acid and the structural formula is represented below:
The molecular formula is C20H32O5 and its molecular weight is 352.5. Dinoprostone occurs as a white to off-white crystalline powder. It has a melting point within the range of 65° to 69°C. Dinoprostone is soluble in ethanol and in 25% ethanol in water. Each insert contains 10 mg of dinoprostone in 241 mg of a cross-linked polyethylene oxide/urethane polymer which is a semi-opaque, beige colored, flat rectangular slab measuring 29 mm by 9.5 mm and 0.8 mm in thickness. The insert and its retrieval system, made of polyester yarn, are non-toxic and when placed in a moist environment, absorb water, swell, and release dinoprostone.
Dinoprostone (PGE2) is a naturally-occurring biomolecule. It is found in low concentrations in most tissues of the body and functions as a local hormone (1-3). As with any local hormone, it is very rapidly metabolized in the tissues of synthesis (the half-life estimated to be 2.5-5 minutes). The rate limiting step for inactivation is regulated by the enzyme 15-hydroxyprostaglandin dehydrogenase (PGDH) (1,4). Any PGE2 that escapes local inactivation is rapidly cleared to the extent of 95% on the first pass through the pulmonary circulation (1,2).
In pregnancy, PGE2 is secreted continuously by the fetal membranes and placenta and plays an important role in the final events leading to the initiation of labor (1,2). It is known that PGE2 stimulates the production of PGF2α which in turn sensitizes the myometrium to endogenous or exogenously administered oxytocin. Although PGE2 is capable of initiating uterine contractions and may interact with oxytocin to increase uterine contractility, the available evidence indicates that, in the concentrations found during the early part of labor, PGE2 plays an important role in cervical ripening without affecting uterine contractions (5-7). This distinction serves as the basis for considering cervical ripening and induction of labor, usually by the use of oxytocin (8-10), as two separate processes.
PGE2 plays an important role in the complex set of biochemical and structural alterations involved in cervical ripening. Cervical ripening involves a marked relaxation of the cervical smooth muscle fibers of the uterine cervix which must be transformed from a rigid structure to a softened, yielding and dilated configuration to allow passage of the fetus through the birth canal (11-13). This process involves activation of the enzyme collagenase which is responsible for digestion of some of the structural collagen network of the cervix (1, 14). This is associated with a concomitant increase in the amount of hydrophilic glycosaminoglycan, hyaluronic acid and a decrease in dermatan sulfate (1). Failure of the cervix to undergo these natural physiologic changes, usually assessed by the method described by Bishop (15,16), prior to the onset of effective uterine contractions, results in an unfavourable outcome for successful vaginal delivery and may result in fetal compromise. It is estimated that in approximately 5% of pregnancies the cervix does not ripen normally (17). In an additional 10-11% of pregnancies, labor must be induced for medical or obstetric reasons prior to the time of cervical ripening (17).
The delivery rate of PGE2 in vivo is about 0.3 mg/hour over a period of 12 hours. The controlled release of PGE2 from the hydrogel insert is an attempt to provide sufficient quantities of PGE2 to the local receptors to satisfy hormonal requirements. In the majority of patients, these local effects are manifested by changes in the consistency, dilatation and effacement of the cervix as measured by the Bishop score. Although some patients experience uterine hyperstimulation as a result of direct PGE2- or PGF2α-, mediated sensitization of the myometrium to oxytocin, systemic effects of PGE2 are rarely encountered. The insert is fitted with a biocompatible retrieval system which facilitates removal at the conclusion of therapy or in the event of an adverse reaction.
No correlation could be established between PGE2 release and plasma concentrations of PGEm. The relative contributions of endogenously and exogenously released PGE2 to the plasma levels of the metabolite PGEm could not be determined. Moreover, it is uncertain as to whether the measured concentrations of PGEm reflect the natural progression of PGEm concentrations in blood as birth approaches or to what extent the measured concentrations following PGE2 administration represent an increase over basal levels that might be measured in control patients.