Dinoprostone Gel (PGE2 Gel) - Comprehensive Overview

What It Is

• Gel (Prepidil): 0.5 mg PGE2 in 2.5 mL, for intracervical administration
• Vaginal insert (Cervidil): 10 mg, designed to release PGE2 at 0.3 mg/h over 12 hours

Mechanism of Action

1. Cervical ripening - relaxes cervical smooth muscle, causing softening, effacement, and dilation
2. Uterine contractions - stimulates myometrial contractions to initiate or augment labor

Indications

• Cervical ripening prior to labor induction (primary FDA-approved indication)
• Labor induction when the cervix is unfavorable (low Bishop score)
• Second-trimester pregnancy termination (in higher doses/formulations)
• Management of intrauterine fetal death (with or without concurrent oxytocin)

Dosing and Administration

Pre-procedure Assessment

• Calculate Bishop score before initiating any induction agent
  • Score >8: success of induction approaches that of spontaneous labor
• Perform a nonstress test (NST) - do NOT proceed if NST is nonreactive or regular contractions are already present
• Confirm gestational age (at least 39 weeks for elective induction)

Catheter Selection

• Use a 20 mm catheter if no cervical effacement is present
• Use a 10 mm catheter if effacement >50%

Procedure Steps (Prepidil 0.5 mg gel)

1. Obtain IV access (optional but advisable)
2. Connect the appropriate shielded catheter to the filled syringe
3. Place patient in dorsal (supine) position; use a speculum for direct visualization
4. Under sterile conditions, insert catheter into the vagina and express 0.5 mg gel into the cervical canal, just below the level of the internal os
5. If catheter disconnects, spread remaining gel onto the cervix manually
6. Each syringe is single-use only; discard after use

Post-procedure

• Patient remains supine for 15 to 30 minutes to minimize leakage
• Maintain external fetal monitoring (FHR + uterine activity) for 2 hours after installation
• Monitoring may be discontinued after 2 hours if no uterine activity or FHR abnormalities occur

Repeat Dosing

• Reassess cervix after 6 hours
• If minimal change in Bishop score, may repeat once after 6-12 hours
• Maximum cumulative dose: 1.5 mg (three doses of 0.5 mg) in a 24-hour period

Storage

Contraindications

• History of asthma (PGF2α is a bronchoconstrictor; caution applies to all prostaglandins; even childhood asthma without adult attacks warrants caution)
• History of glaucoma
• History of myocardial infarction
• Previous uterine hypertonia
• Ruptured membranes (use with caution; requires sterile technique)
• Grand multiparity, previous caesarean section, malpresentations, unexplained vaginal bleeding, prematurity (all relative contraindications to induction generally)

Adverse Effects

Comparison with Other Agents

A meta-analysis of RCTs comparing dinoprostone with misoprostol found shorter time to delivery and lower cesarean delivery rates with misoprostol - though misoprostol remains off-label for this use. - Pfenninger & Fowler's Procedures for Primary Care

Key Clinical Points

1. Both oxytocin and dinoprostone are the only agents FDA-approved for labor induction.
2. Oxytocin should not be started until at least 30 minutes after removing the dinoprostone insert; at least 3 hours after the last misoprostol dose.
3. PGE2 has no antidiuretic effect (unlike oxytocin), making it theoretically better in patients with preeclampsia or cardiac/renal disease, though clinical benefit is not well documented.
4. Neither PGE2 nor PGF2α causes significant cardiovascular toxicity at doses used for induction. PGE2 would need to be infused ~20x faster than the labor-induction rate to cause blood pressure changes.
5. The vaginal insert formulation offers the practical advantage that hyperstimulation can be quickly reversed by removing the device using its attached tape.