Cervical Capsaicin for Labor Induction and Pain Relief

Induction of labor is associated with increased risk of cesarean section and elevated pain when compared to labor of spontaneous onset (1,2). In the setting of intrauterine fetal demise (IUFD), it is desirable to induce labor in order to achieve a successful vaginal delivery for the health and well being of the mother, thereby avoiding operative fetal extraction.

The current protocol for midtrimester labor induction prior to 24 weeks gestational age includes intravaginal cytotec(misoprostol) 200 mcg every 6 hours for up to 24 hours, occasionally followed by oxytocin infusion. When an IUFD occurs at 24 or greater weeks gestational age, labor is induced with cytotec 25 or 50 mcg every 4 hours and/or oxytocin infusion.

We hypothesize that application of lidocaine to the uterine cervix followed by 0.1% capsaicin cream will facilitate cervical ripening and decrease the pain of labor induction when compared to use of a placebo cream. Capsaicin 8methylNvannilyl6nonenamide) activates TRPV1, a nonselective cation channel activated directly by heat, and low pH, and indirectly by a number of inflammatory factors, including nerve growth factor (NGF), bradykinin, lipids, and prostaglandins. Activation of TRPV1 by capsaicin results in an influx of Ca2 and Na ions, depolarization, exocytosis of neuropeptides and excitatory amino acids, and induces a burning sensation. This initial phase is followed by prolonged desensitiztion that is dose dependent. Once the TRPV1 receptor is desensitized, pain transmission through Ctype primary afferent receptors is reduced. The pain relief from capsaicin is due to desensitization of the TRPV1 receptor. The enhancement of cervical ripening is due to activation of primary afferent Cfibers, release of neuropeptides substance P, neurokinin A, calcitonin generelated peptide, secretoneurin and nitric oxide to help orchestrate a series of local inflammatory responses including vasodilation, vascular permeability with tissue edema and protein extravasation, and migration of inflammatory immune cells(3).In a study of pregnant rats, vaginal lidocaine gel was applied followed by capsaicin sham cream. A blinded observer monitored behavior via video over the next 72 hours. All animals treated with capsaicin delivered on day 22 with minimal pain behaviors while 90% of sham treated animals delivered as expected on day 23 with normal pain related behavior. All pups were delivered live and rearing and suckling behavior was normal (unpublished data).