Pharmacokinetics of Intravenous Oxytocin and Effects on Sensory Function in Healthy Volunteers
Phase: PHASE4
Conditions: Chronic Pain
Sponsor: Wake Forest University Health Sciences

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Pharmacokinetics of intravenous oxytocin and effects on sensory 
function in healthy volunteers 
 
IRB00056413 
NCT03929367 
Version Date: 6/11/2019 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

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BACKGROUND 
 
A large body of evidence in animals and in humans suggest that oxytocin can 
produce analgesia to experimental pain stimuli and relieve pain in acute and chronic 
clinical pain states.  For the past 8 years we have, under an NIH MERIT award, tested 
the role of the spinal cord in oxytocin’s actions by studies in rodents and clinical trials, 3 
of which are ongoing, of spinally injected oxytocin. 
 
The Pain Mechanisms Laboratory at Wake Forest is now in the process of 
assembling an NIH program project grant (P01) on the topic of oxytocin sites, 
mechanisms, and clinical applications for analgesia, and Dr. Eisenach will lead the 
clinical project in that proposal.  This IRB protocol is meant to obtain preliminary data 
critical to that NIH application in September, 2019. 
 
Determining the site(s) of action of oxytocin for analgesia in humans is critical to 
future clinical trials and drug development.  We will propose to use computer-controlled 
intravenous infusions of oxytocin to rapidly achieve and maintain targeted plasma 
concentrations.  By locking plasma concentrations and examining a wide concentration 
range, coupled with testing aimed to measure activity of oxytocin on peripheral nerves, 
in the spinal cord, and in the brain, we plan to identify infusion regimens that only target 
1 or 2 of these sites for clinical trials. 
 
WHY WE NEED TO DEFINE PHARMACOKINETICS OF OXYTOCIN 
 
In this IRB protocol we take the necessary first step towards computer-controlled 
intravenous infusions of oxytocin.  In this protocol we will describe the pharmacokinetics 
of intravenous oxytocin in healthy non-pregnant adult men and women.  We cannot 
program infusion devices for targeted concentrations without knowledge of oxytocin’s 
pharmacokinetics in this population of interest.  Although much is known of the 
pharmacodynamics of intravenous and intramuscular oxytocin to cause uterine 
contraction during pregnancy and in the postpartum period, we know virtually nothing 
about oxytocin’s pharmacokinetics in this setting and nothing in the nonpregnant 
population.  This reflects the fact that immunoassays used to measure oxytocin for the 
past 3 decades suffer critical limitations because the antibodies used are confounded by 
binding to oxytocin degradation products, particularly those that are tightly bound to 

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circulating proteins and presenting a large background of antigenicity to which these 
antibodies bound.  In a recent review of the state of our lack of knowledge regarding 
oxytocin disposition, it was noted that reports differ in resting and infused oxytocin 
concentrations in plasma by 2 to 3 orders of magnitude, and that the use of these 
assays essentially generate random numbers with no basis in reality [8]. 
 
Beginning in 2016 reports appeared of highly sensitive and specific assays of 
oxytocin in plasma and other biofluids using liquid chromatography coupled with mass 
spectroscopy (LC-MS) [2; 3; 6; 11].  A recent report included pharmacokinetics of 
oxytocin after intramuscular injection using LC-MS [3] with concentrations assayed by a 
commercial entity (Syneos Health, Princeton, NJ).  We have secured a quote from this 
company and will use them to measure oxytocin in de-identified samples from this 
protocol sent to their facility.  We note that pharmacokinetics from intramuscular 
administration cannot alone inform computer controlled infusion of intravenous oxytocin, 
necessitating data from this IRB protocol. 
 
RATIONALE FOR OTHER MEASURES BEYOND BLOOD SAMPLES IN THIS PROTOCOL 
 
Although the primary goal of this protocol is to model change in oxytocin 
concentrations in plasma after intravenous administration, we will also acquire tests of 
sensory function that could be modulated by oxytocin during later time periods when 
blood samples are widely separated by time.  There are two measures which will 
assess two different aspects of sensory function. 
MEASURE 1: LIGHT TOUCH FREQUENCY THRESHOLD 
 
Light touch is subserved by a group of myelinated peripheral nerves with fast 
conduction in the Aβ range and which are capable of following high frequencies, being 
responsible for the sensation of vibration.  This capability of individual nerve fibers to 
respond with high frequency also underlies our ability to sense a light touch moving 
across the body surface as in brushing. 
 
In preclinical studies we have shown that, following injury, these light touch fibers 
lose their ability to follow high frequencies and, in some cases, no longer respond to 
mechanical stimulation at all [1].  Oxytocin, when perfused around the neuronal cell 

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bodies of these Aβ nerve fibers, partially restores their function, including their response 
to high frequency stimulation. 
 
In order to determine the highest frequency that Aβ nerve fibers can respond to, 
we have created a simple device that produces an oscillatory / vibratory stimulus which 
can be used on the hand.  The subject places fingertips and volar aspect of the wrist 
sequentially and the device is set to slowly decrease the frequency of vibration from 1 
kHz until the subject first perceives this.  This is repeated three times at each site and 
takes under 5 minutes in total.  More details are provided in the Appendix. 
 
We anticipate that oxytocin will have no effect on normal Aβ fibers and that this 
measure will not change after oxytocin administration.  This will provide important data 
to contrast with the expected efficacy of oxytocin in the setting of injury, to be studied in 
subsequent protocols. 
MEASURE 2: SUSTAINED HEAT 
 
As part of a protocol used by us in several studies, the surface of the skin of the 
forearm or leg is heated to 45°C using an FDA approved, Peltier-controlled thermode for 
a period of 5 minutes (TSA®, Medoc, Ramat Yishai, Israel).  This typically results in a 
slowly increasing pain experience, peaking at 5 minutes in the mild to low moderate 
range and has been tolerated by more than 150 subjects in studies over the past 14 
years. 
 
In an interim analysis of an ongoing clinical study 
in volunteers, we noted that spinal injection of oxytocin, 
15 μg (equivalent to 9 IU), that pain from this sustained 
heat was dramatically reduced over the 5 minutes of 
stimulus presentation (adjacent figure). In contrast, 
spinal oxytocin had no effect on the stimulus-response 
relationship of pain to noxious heat over a 42-50°C 
range when the stimuli were presented for only 5 
seconds.  These data suggest that oxytocin reduces C-
fiber mediated signaling of sustained heat pain, likely 
through a spinal site of action.  
 
Drugs administered spinally have a much higher 

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concentration in cerebrospinal fluid than plasma.  Nonetheless, spinally administered 
drugs are typically absorbed to an extent and with a time course similar to that after 
intramuscular injection, and it is conceivable that the effect on sustained heat pain we 
are seeing in the spinal study reflect peripheral effects via systemic absorption.  Thus, if 
we see a similar reduction in response to sustained heat in this protocol of intravenous 
administration, we will conclude that oxytocin is more likely activing peripherally than 
spinally. 
 
 

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Protocol 
Pharmacokinetics of intravenous oxytocin and effects on sensory 
function in healthy volunteers 
 
PRIMARY GOAL:  Measure oxytocin in plasma after brief intravenous infusion and model 
its pharmacokinetics. 
 
METHODS:  Equal numbers of healthy adult men and women will be recruited (ten 
total).  At least 1 day prior to study subjects will be trained to rate pain in response to 
heat applied to the lateral calf using a Peltier controlled thermode and to indicate when 
they first perceive a vibratory stimulus on the fingertips and wrist.   
Subjects will return for study visit two in which an intravenous catheter will be 
inserted in the arm and, after baseline measures of response to heat and determination 
of vibration frequency threshold, subjects will receive oxytocin (Pitocin®), 10 IU over  10 
minutes.  Venous blood samples (5 ml) will be obtained before and at 2, 5, 10, 15, 30, 
45, 60, 90, 120, 180, and 240 minutes after the end of the oxytocin administration by 
removal of blood from the intravenous catheter. 
 We will abandon an individual participant's study and schedule another 
participant should we be unable to successfully place the intravenous catheter. 
 
STUDY DESIGN 
Inclusion Criteria: We request permission to study up to 12 subjects so that we will 
have 10 evaluable subjects with complete sampling at all time periods. 
1. Male or female > 18 and < 60 years of age, Body Mass Index (BMI) <40. 
2. Generally in good health as determined by the Principal Investigator based on 
prior medical history, American Society of Anesthesiologists physical status I or II 
3. Normal blood pressure (systolic 90-140 mmHg; diastolic 50-90 mmHg) resting 
heart rate 45-100 beats per minute) without medication 
4. Female subjects of child-bearing potential and those < 1 year post-menopausal, 
must be practicing highly effective methods of birth control such as hormonal methods 
(e.g., combined oral, implantable, injectable, or transdermal contraceptives), double 
barrier methods (e.g., condoms, sponge, diaphragm, or vaginal ring plus spermicidal 

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jellies or cream), or total abstinence from heterosexual intercourse for a minimum of 1 
full cycle before study drug administration. 
Exclusion Criteria: 
 
1. Hypersensitivity, allergy, or significant reaction to any ingredient of Pitocin® 
2. Any disease, diagnosis, or condition (medical or surgical) that, in the opinion of 
the Principal Investigator, would place the subject at increased risk (active gynecologic 
disease in which increased tone would be detrimental e.g., uterine fibroids with ongoing 
bleeding), compromise the subject’s compliance with study procedures, or compromise 
the quality of the data 
3. Women who are pregnant (positive result for serum pregnancy test at screening 
visit), women who are currently nursing or lactating, women that have been pregnant 
within 2 years 
4. Subjects with neuropathy, chronic pain, diabetes mellitus, or taking 
benzodiazepines or pain medications on a daily basis. 
 
Study Visit 1:  The participant will report to the Clinical Research Unit (CRU) or 
Piedmont Plaza II  at least 1 day prior to study visit 2. The participant will review and 
sign the Informed Consent. After informed consent is adequately obtained, a detailed 
medical history will be obtained from the participant, female participants will have a 
urine sampled tested   to determine pregnancy status.  The research nurse will train the 
participants to estimate pain quantitatively using a 2 cm2 Peltier controlled thermode 
(TSA®) applied to a forearm with 5 sec presentation of stimuli at 39, 41, 43, 45, 47, 49, 
and 50°C, using a 11 point numerical verbal scale (NRS) anchored at 0 for no pain and 
10 for the worst pain imaginable.  Typically, the participant is exposed to temperatures 
between 380 and 510 C using a random staircase method. After this training, we will ask 
them to report pain intensity on the 0-10 NRS scale every minute for 5 minutes upon 
exposure to a 4 cm2  Peltier controlled thermode at 45°C.  Finally, they will place first the 
fingertips of their hand and then the volar wrist, on a device and report when they first 
perceive a sensation as the surface vibration frequency declines from 1 kHz to 1 Hz. 
We have found this training session significantly reduces anxiety and variability in pain 
and hypersensitivity ratings on subsequent study days.  

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Study Visit 2  
On the second visit, the participant will report to the CRU, in the morning after 
having had nothing to eat or drink since midnight. A peripheral intravenous catheter will 
be inserted into a vein in an upper extremity and lactated Ringers solution infused at 1.5 
ml/kg/hr for the duration of the study. After obtaining baseline measures (random 
presentation of 5 sec heat stimuli between 39 and 50°C, 5 minute presentation of a 
45°C stimulus, and vibration frequency perception threshold as described in Visit 1), 
oxytocin (Pitocin®, 10 IU) will be administered intravenously over 10 minutes. 
Venous blood will be sampled (5 ml) before the infusion and at 2, 5, 10, 15, 30, 45, 
60, 90, 120, 180, and 240 minutes after oxytocin injection via the indwelling intravenous 
catheter.  We will also repeat vibration frequency perception threshold in fingertips  and 
wrist between the samples after samples at 5, 
20, 45, 60, 120, and 180 minutes.  In addition, 
we will ask them to rate pain intensity every 
minute for 5 minutes with a 45° stimulus after 
samples at 30, 60, 120, and 180 minutes (adjacent figure) and rate pain intensity to 
single, 5 second duration stimuli from 39°C to 50°C after samples at 60, 120, and 180 
minutes as on the first visit.  
Safety and Monitoring: 
 
Assessment of Side Effects:  Significant side effects are defined as changes > 30% 
from baseline in the mean arterial pressure, HR, or oxyhemoglobin pulse oximetry < 90. 
Any unexpected or serious side effects will be reported to the IRB within 24 hrs. 
Peripheral oxyhemoglobin saturation, BP and HR will be measured non-invasively 
before and 15, 30, 60, 120, 180, 240, minutes after intravenous oxytocin injection. If 
either BP or HR change by > 30%, or oxyhemoglobin saturation decreases to less than 
90, and require treatment, these vital signs will be repeated at 5-minute intervals until 
vital signs are stabilized.  
Treatment of Side Effects: Mean blood pressure elevations greater than 30% of 
baseline will be treated with labetalol 5-15 mg IV incrementally until BP elevation is less 
than 30% elevated. Reductions in mean BP > 30% of baseline will be treated with 
incremental ephedrine 5-20 mg, IV. Heart rate (HR) reductions or elevations > 30% of 

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baseline will be treated with incremental glycopyrolate 0.2 mg IV or propranolol 0.2 mg 
IV, respectively. Peripheral oxyhemoglobin desaturation (< 90) will be treated with 
supplemental oxygen, nasal cannula, face mask, or non-rebreathing mask depending 
upon the degree desaturation and the response to therapy.  
 
RISKS 
 
Risks of intravenous cannulation include pain on insertion and bruising at the 
site.  Risks from the FDA approved heat stimulus device are pain, and the subject can 
stop testing at any time if the pain they perceive is such that they do not want to 
continue.  Please note that these devices are used in many pain clinics routinely and 
have multiple fail-safe designs to avoid thermal burn.  Risks from the non-regulatory 
vibratory device are related only to microshock and are addressed in the Appendix. 
 
Risks of oxytocin are primarily restricted to uterine contraction in the presence of 
pregnancy, since oxytocin receptors are not present in the non-pregnant uterus 
(Package insert attached). 
Additionally there is the possibility of a feeling of being flushed, headache and 
increased heart rate with no significant change in blood pressure during or immediately 
after the infusion. These events have been reported by previous participants but were 
short lived, lasting approximately 12-15 minutes. 
 
 
HUMAN SUBJECTS 
All studies in volunteers will be performed in the CRU, which includes monitoring 
and resuscitation equipment and trained nursing support staff, or in in-patient settings of 
the Wake Forest Baptist Medical Center. All studies will be approved by the IRB and 
written informed consent obtained. The Project Investigators have all performed similar 
studies in volunteers and patients. The purpose of the study and all risks will be 
discussed with each volunteer, and all questions will be answered prior to obtaining 
written informed consent. Risks to be discussed include discomfort with needle and 
catheter insertion. All data acquired will remain confidential with no reference to 
individuals in publications.   

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Data Safety Monitoring Plan 
 
Although the use of oxytocin in this protocol is outside FDA approval for oxytocin 
administration during labor or in the postpartum period, the dose to be studied is similar 
to or less than that of multiple recent studies in healthy volunteers with intranasal 
oxytocin purchased over the counter in the US [4-7; 9-21] and without description of 
adverse events.  For these reasons, we do not propose a data safety monitoring 
committee or special safety evaluation beyond those required by IRB regulations. 
Minority, Gender, and Children Participation 
Both sexes and races and ethnicities will be actively recruited in this small study.  
Children under age 18 are not included in these protocols because this protocol 
because the safety of this product has not been established in children.  
 
Volunteer Payment 
Participants will be paid a total of $300 according to the following payment 
schedule which we have used throughout the last 2 cycles of this grant's protocols. We 
believe that this payment schedule is fair and appropriate, paying for each procedure 
attempted and an additional payment for completion of the entire study.  
Completion of study 1: $25 
Placement of IV: $25 
Completion of entire study: $250 
Volunteer must complete all of the above phases to receive this payment. 
 
Long-term Follow-up 
Volunteers will be contacted daily within the following week and questioned about 
adverse events from the study. 
 
STATISTICAL RATIONALE 
Primary outcome measure is the concentration of oxytocin in plasma at defined times 
after intravenous infusion.  We request a convenience sample of 10 subjects for the 
purpose of preliminary data to provide variance estimates that will inform federal grant 

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submission for use of the pharmacokinetic parameters from this sample or proposal of a 
larger sample size to adequately characterize such parameters.  
 
 
 
 
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