Intranasal and Intravenous Oxytocin for Analgesia to Noxious Heat Pain

This protocol will utilize a randomized, triple-masked, cross-over study design to compare intravenous (IV) to intranasal (IN) oxytocin administration for analgesia to an experimental pain stimulus in healthy volunteers. Equal numbers of adult men and women; ages 18-55 will be recruited. Participants will report to the research unit for three visits, 1) screening, informed consent, pregnancy test, and training to consistently rate pain from an FDA-approved device to test heat pain. The lowest temperature which causes a pain score of greater than 2 with 5 minutes of heating will be identified, 2) intravenous infusion and self-administered intranasal spray of study drug and 5-minute heat testing at intervals for 4 hours, 3) a repeat of the procedures done at visit two.

Participants will receive intravenous oxytocin, 20 IU and intranasal placebo on one of these visits and intravenous placebo and intranasal oxytocin, 48 IU, on the other. Pain score at the end of 5-minute skin heating will be compared using mathematical modeling of the time course of change in each individual and in the study population as a whole. The effect, if any, on these models of participant age, sex, and weight will be explored.

• Intravenous oxytocin (Drug), also known as Pitocin: Oxytocin, 10 International Units (IU) will be administered by IV infusion over 30 minutes and, 30 minutes later, a second 10 IU will be administered over 30 min, for a total dose of 20 IU. The first infusion will be at a rate of 0.125 IU/min for the first 5 min, then at 0.375 IU/min for the remaining 25 min. The second 30-min infusion will be at a fixed rate of 0.333 IU/min.
• Intravenous placebo (Drug), also known as Normal saline: Saline will be administered as two 30-min IV infusions separated by 30-min, using the same volume of infusion solution and rates of administration as in the intravenous oxytocin intervention.
• Intranasal oxytocin (Drug), also known as Pitocin: Oxytocin will be self-administered at the time the first IV infusion begins as a single 0.1 mL spray (12 IU) in each nostril followed in 5 min by another spray in each nostril. The total dose of oxytocin is 48 IU.
• Intranasal placebo (Drug), also known as Excipients: chlorobutanol, methylparaben, propylparaben, dibasic sodium phosphate, anhydrous citric acid, sorbitol, glycerin, and sterile water: Placebo (solution containing the excipients in the oxytocin solution but without oxytocin) will be self-administered at the time the first IV infusion begins as a single 0.1 mL spray in each nostril followed in 5 min by another spray in each nostril.

Primary outcomes

• Pain Scale Score - End of 5-minute Skin Heating [Baseline Up to Hour 4.5]: Change in verbal pain scale score. Range is 0-10. 0 is equivalent to no pain and 10 is equivalent to the worst pain imaginable.
• Pain Scale Score - During Skin Heating [Minute 5 During Skin Heating]: Verbal pain scale range is 0-10. 0 is equivalent to no pain and 10 is equivalent to the worst pain imaginable.

Secondary outcomes

• Pain Scale Score - During Skin Heating [Minute 1 During Skin Heating]: Verbal pain scale range is 0-10. 0 is equivalent to no pain and 10 is equivalent to the worst pain imaginable.
• Pain Scale Score - During Skin Heating [Minute 2 During Skin Heating]: Verbal pain scale range is 0-10. 0 is equivalent to no pain and 10 is equivalent to the worst pain imaginable.
• Pain Scale Score - During Skin Heating [Minute 3 During Skin Heating]: Verbal pain scale range is 0-10. 0 is equivalent to no pain and 10 is equivalent to the worst pain imaginable.
• Pain Scale Score - During Skin Heating [Minute 4 During Skin Heating]: Verbal pain scale range is 0-10. 0 is equivalent to no pain and 10 is equivalent to the worst pain imaginable.

Sex: All, ages: 18 Years to 75 Years, accepts healthy volunteers

Inclusion Criteria:

* Male or female > 18 and ≤75 years of age, Body Mass Index (BMI) <40.
* Generally in good health as determined by the Principal Investigator based on prior medical history, and as assessed to be American Society of Anesthesiologists physical status 1, 2, or 3.

Exclusion Criteria:

* Recent (<3 months) nasal surgery or chronic conditions requiring daily intranasal (IN) medications
* Hypersensitivity to any ingredient in Pitocin® (marketed preparation of oxytocin for parenteral injection)
* Latex allergy
* Any disease, diagnosis, or condition (medical or surgical) that, in the opinion of the Principal Investigator, would place the subject at increased risk (e.g., active gynecologic disease in which increased tone would be detrimental such as uterine fibroids with ongoing bleeding)
* Women who are pregnant, are currently nursing or lactating, or have been pregnant within 2 years
* Neuropathy, chronic pain (located in any body location that is being treated), diabetes mellitus, or taking benzodiazepines or pain medications on a daily basis.
* Current or history of ventricular tachycardia, atrial fibrillation or prolonged QT interval.
* Past or current history of hyponatremia or at risk for hyponatremia; anyone taking thiazide diuretics, loop diuretics, combination diuretics, lithium, carbamazepine, enalapril, ramipril, celecoxib, temazepam, gliclazide, glimepiride, glibenclamide, glipizide, omeprazole, pantoprazole, desmopressin, serotonin selective reuptake inhibitors (SSRI's), monamine oxidase inhibitors (MAOI), or the recreational drug ecstasy.

• Informed Consent Form (PDF, 2025-11-24)

• James C Eisenach, MD, Principal investigator, Atrium Health Wake Forest Baptist