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Figure 1. Dinoprostone.
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Labor is induced in approximately 20% of pregnancies in Europe and North America. Labor induction in patients with an unfavorable cervix is associated with a higher incidence of prolonged labor and higher rates of operative and cesarean delivery [1,2]. In 1964, Bishop introduced a cervical scoring system used to determine the condition of the cervix based on dilation, effacement, station, position and consistency [3]. Cervical ripening prior to induction is often utilized in women who have a Bishop score of less than 6. Prostaglandins (PGs) have been used with great success in various formulations for the induction of labor and cervical ripening [4]. Dinoprostone (PGE2) has been used in this capacity since the 1970s. PGs used for cervical ripening lead to shorter labor, less use of oxytocin and greater likelihood of vaginal delivery within 24 h compared with placebo [5].
Dinoprostone, administered vaginally or intracervically, is effective for cervical ripening [4-12]. Due to the risk of systemic side effects with the use of PGs, various formulations for local application have been developed. These applications include vaginal tablets, vaginal suppositories, vaginal and intracervical gels that are dispensed in a single use syringe, and sustained-release intravaginal inserts. Tablets and suppositories are easy to place but there is a wide variation in effects and these effects are difficult to predict [13]. While vaginal or intracervical gel formulations are effective in cervical ripening, proper insertion may be difficult and requires an experienced clinician. Intracervical placement can lead to uterine hyperstimulation if passed into the extra-amniotic space, and may also lead to decreased efficacy if spillage occurs from the cervical canal into the vagina [13]. Uterine hyperstimulation syndrome is defined as tachysystole (greater than five contractions in 10 min) or hypertonus (contractions lasting longer than 90 s) associated with fetal tachycardia, late decelerations, fetal bradycardia and/or the loss of beat-to-beat variability [14]. Uterine hyperstimulation may occur due to rapid delivery of a PG. Administration of PG via a gel, tablet or suppository make it nearly impossible to retrieve the medication once absorption has occurred. A proprietary sustained- and controlled-release formulation of dinoprostone is available that addresses these potential problems associated with tablets, suppositories and gels.
A sustained- and controlled-release 10 mg...