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).