Human Experimental Models of Pain (HEMP)

A Pilot Study for Developing a Comprehensive Signal Detection Approach for the Mechanisms of Action and Analgesic Efficacy of Two Analgesics Using Human Experimental Models of Pain (HEMP)

This pilot study will test an innovative way to establish how pain medicines provide analgesia in healthy adults. The study uses a group of short, controlled pain tests to look at different types of pain responses in the body. The main goal is to find out if this testing approach can show the pain-relieving effects of 2 medicines, pregabalin and naproxen versus placebo, and show how they provide relief of different types of pain.

The study hypothesis is that this pain testing approach administered as a battery would be able to tell the difference between a medicine that works mainly in the brain and spinal cord (pregabalin) and a medicine that works mainly on inflammation in body tissues (naproxen).

Up to 25 healthy adults will take part. Each participant will receive all 3 study treatments, pregabalin, naproxen, and placebo, administered in random order during separate study periods. The order will be assigned by chance. Neither the participant nor the study team will know which treatment is given at each visit.

The study includes several experimental pain tests. These include:

a heat and capsaicin skin test that causes short-term skin sensitivity,

a UVB light test that causes a temporary sunburn-like sensitivity, and

a cold pressor test, in which a hand is placed in very cold water for a short time.

Participants will also have sensory testing to measure how they feel touch, pressure, pinprick, warmth, heat, and cold. Blood samples will be collected to measure study drug levels. Urine samples, vital signs, and other safety checks will also be done.

Each treatment visit includes testing before and for several hours after taking the study drug. There will be a washout period of at least 48 hours between treatments. Total participation may last up to about 10 weeks.

This study is not expected to provide direct medical benefit to participants. The information learned may help researchers improve early testing of future pain treatments....

Study Overview

• Status: Not yet recruiting
• Conditions: Acute Pain
• Intervention / Treatment: Drug: Placebo; Drug: Naproxen; Drug: Pregabalin

Detailed Description

Study Description:

This pilot study is designed to validate the performance characteristics of HEMP. This pilot study is a single-center, randomized, double-blind, three-period, three-treatment crossover designed to investigate how well the HEMP model distinguishes the analgesic properties of two medications, one which acts centrally and the other one acts peripherally.

Up to 25 healthy adults will be enrolled in this study, which will consist of a screening phase and a treatment phase with three periods. Participants will be randomly assigned to receive either a gabapentinoid (pregabalin), a non-steroidal anti-inflammatory drug (NSAID) (naproxen), or a placebo during each period of the treatment phase (see Table 2 for the study drugs). Each dose will be separated by a wash-out period of at least 48 hours.

Assessments will be performed at baseline and over a period of 8 hours following each drug administration to establish pharmacodynamic, pharmacokinetic, and safety properties of the treatments.

Objectives:

Primary Objective:

To establish the ability of HEMP to demonstrate the analgesic efficacy of pregabalin and naproxen based on their known mechanisms of action (central vs. peripheral, respectively) as measured by the severity of experimental pain, allodynia, and hyperalgesia across three pain models.

Secondary Objectives:

To demonstrate that HEMP can determine factors that differentiate responders from non-responders to the study drugs, when evaluating their analgesic properties of these drugs in humans.

Endpoints:

Pharmacodynamics (PD) Primary Endpoint:

• Change from baseline in pain intensity (PI) visual analog scale (VAS) score for allodynia (soft brush) after first heat/capsaicin application (HCM)
• Change from baseline in PI VAS score for hyperalgesia (pin-prick) after first HCM
• Change from baseline in PI VAS score for hyperalgesia (pin-prick) ultraviolet (UVB) light exposure.
• Change from baseline in PI VAS score for heat hyperalgesia (thermal-heat pain) UVB
• Change from baseline in PI VAS score after hand removal in Cold Pressor Test (CPT), i.e., cold water immersion

Secondary Endpoints:

• Weighted mean (based on area under the curve (AUC)) VAS score for spontaneous pain over 0-60 mins following first and second HCM.
• Area of secondary hyperalgesia to pin-pick after HCM following first and second HCM
• Change from baseline in PI VAS score for thermal-heat hyperalgesia following first and second HCM
• Proportion of participant who had at least 30% reduction in PI VAS scores from baseline after a Quantitative Sensory Testing (QST) measure (soft brush, light pressure, pin-prick, thermal contact- warm, thermal contact-heat pain, cold) after first and second HCM and UVB PK parameters (e.g., AUClast, Clast, Cmax, tmax)

• Study Type: Interventional
• Enrollment (Estimated): 25
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Miroslav Backonja, M.D.; Phone Number: (301) 402-5679; Email: misha.backonja@nih.gov

Study Locations

• United States
  • Maryland
    • Bethesda, Maryland, United States, 20892
      • National Institutes of Health Clinical Center
      • Contact: NIH Clinical Center Office of Patient Recruitment (OPR); Phone Number: TTY dial 711 800-411-1222; Email: ccopr@nih.gov

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: Yes

Description

• INCLUSION CRITERIA:

For an individual to be eligible to participate in this study, they must meet all of the following criteria:

• Voluntarily consent to participate and provide written informed consent prior to the start of any study-specific procedures.
• Read and speak English fluently.
• State willingness to comply with all study procedures and availability for the duration of the study.
• Are not pregnant or breastfeeding.
• Are 18 or older years of age at screening.
• Have a skin type score between 2 and 5 (inclusive) on the Fitzpatrick Scale.
• Must correctly identify at least nine out of 12 temperatures (32 degrees Celsius, 38 degrees Celsius, 44 degrees Celsius, and 50 degrees Celsius, each presented three times) during the sensory discrimination test at screening.
• Provide a verbal pain rating between 4 and 9 (inclusive) during the intradermal capsaicin challenge at screening. The study team will verify tolerability, and participants will continue only after it has been confirmed.
• During the cold pressor test at screening, provide a verbal pain rating between 4 and 9 (inclusive) and keep one hand completely immersed in ice-cold water (1-4 degrees Celsius) between 1 and 4 minutes (inclusive). The study team will verify tolerability, and participants will continue only after it has been confirmed.
• Are able to learn and perform all quantitative sensory testing QST procedures (see the separate QST manual).
• Have the ability to take oral medication and be willing to adhere to the study intervention regimen.

EXCLUSION CRITERIA:

An individual who meets any of the following criteria will be excluded from participation in this study:

• Have a history or presence of clinically significant cardiovascular, pulmonary, hepatic, renal, hematologic, gastrointestinal, endocrine, immunologic, dermatologic, neurologic, oncologic, or psychiatric disease or any other condition that, in the opinion of the Investigator, would jeopardize the safety of the participant or the validity of the study results.
• Have alcohol or drug dependence (excluding nicotine and caffeine) within the past 2 years, as defined by the Diagnostic and Statistical Manual of Mental Disorders, 4th edition, text revision (DSM IV-TR) and/or participants who have ever been in a substance or alcohol rehabilitation program to treat their substance dependence are currently seeking such treatment.
• Have a clinically significant abnormal finding on the physical exam, medical history, or clinical laboratory results at screening.
• Have a history of psychotic reactions, a non-psychotic emotional disorder, or another mental illness that, in the opinion of the investigator, may affect the ability of the participant to participate in the study.
• Have recent history of suicidal ideation or suicidal behavior within the past 6 months, as assessed by the Columbia- Suicide Severity Rating Scale (C-SSRS) at screening (baseline version) or at check-in ( Since Last Visit version).
• Have a history of allergy or hypersensitivity to pregabalin or other gabapentinoids, naproxen or other NSAIDs, or another ingredient in the study drugs, or anything else that, in the opinion of the Investigator, could put the participant at risk.
• Have participated in another clinical trial (randomized participants only) within 30 days prior to the first dose of study medication.
• Use any prescription medication, except hormonal contraceptive or hormonal replacement therapy, from 14 days prior to the first dose of study medication until study participation has ended without evaluation and approval by the Investigator.
• Donate blood or plasma within 30 days prior to the first dose of study medication until the end of study participation. It is recommended that participants not donate blood or plasma until at least 30 days after their study participation has ended.
• Female participants who are currently pregnant or breastfeeding, or who are planning to become pregnant during the study or within 30 days after the last study drug administration.
• Show a positive urine alcohol test at screening.
• Have smoked or used tobacco- or nicotine-containing products within 30 days prior to the first dose of study treatment until the end of the study.
• Have an allergy to capsaicin or another capsaicinoid.
• Have a tattoo, excessive scarring or discoloration, keloid formation, or, at the Investigator s discretion, otherwise unhealthy skin (e.g., eczema, psoriasis, burn, and cut) at a QST site.
• Have a significant history of nerve injury or damage at a QST site, at the Investigator s discretion.
• Participants who report any stimulus as intolerable at any point during the screening procedures will be excluded from participation.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: Triple

Number of Arms

6

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Sequence ABC (Pregabalin - Naproxen - Placebo); Participants assigned to this sequence will receive single-dose oral pregabalin 300 mg in Period 1, naproxen 550 mg in Period 2, and matching placebo in Period 3. Treatment periods are separated by at least 48 hours.	Drug: Placebo; Over-encapsulated matching placebo administered as a single oral dose in one treatment period of this randomized, double-blind, 3-period crossover study. The placebo is made to look identical to active study drug capsules to maintain blinding. Each participant receives placebo once, with at least 48 hours washout between treatment periods.; Drug: Naproxen; Over-encapsulated oral naproxen, 550 mg, administered as a single dose in one treatment period of this randomized, double-blind, 3-period crossover study. Each participant receives naproxen once, with at least 48 hours washout between treatment periods.; Drug: Pregabalin; Over-encapsulated oral pregabalin, 300 mg, administered as a single dose in one treatment period of this randomized, double-blind, 3-period crossover study. Each participant receives pregabalin once, with at least 48 hours washout between treatment periods.
Experimental: Sequence ACB (Pregabalin - Placebo - Naproxen); Participants assigned to this sequence will receive single-dose oral pregabalin 300 mg in Period 1, matching placebo in Period 2, and naproxen 550 mg in Period 3. Treatment periods are separated by at least 48 hours.	Drug: Placebo; Over-encapsulated matching placebo administered as a single oral dose in one treatment period of this randomized, double-blind, 3-period crossover study. The placebo is made to look identical to active study drug capsules to maintain blinding. Each participant receives placebo once, with at least 48 hours washout between treatment periods.; Drug: Naproxen; Over-encapsulated oral naproxen, 550 mg, administered as a single dose in one treatment period of this randomized, double-blind, 3-period crossover study. Each participant receives naproxen once, with at least 48 hours washout between treatment periods.; Drug: Pregabalin; Over-encapsulated oral pregabalin, 300 mg, administered as a single dose in one treatment period of this randomized, double-blind, 3-period crossover study. Each participant receives pregabalin once, with at least 48 hours washout between treatment periods.
Experimental: Sequence BAC (Naproxen - Pregabalin - Placebo); Participants assigned to this sequence will receive single-dose oral naproxen 550 mg in Period 1, pregabalin 300 mg in Period 2, and matching placebo in Period 3. Treatment periods are separated by at least 48 hours.	Drug: Placebo; Over-encapsulated matching placebo administered as a single oral dose in one treatment period of this randomized, double-blind, 3-period crossover study. The placebo is made to look identical to active study drug capsules to maintain blinding. Each participant receives placebo once, with at least 48 hours washout between treatment periods.; Drug: Naproxen; Over-encapsulated oral naproxen, 550 mg, administered as a single dose in one treatment period of this randomized, double-blind, 3-period crossover study. Each participant receives naproxen once, with at least 48 hours washout between treatment periods.; Drug: Pregabalin; Over-encapsulated oral pregabalin, 300 mg, administered as a single dose in one treatment period of this randomized, double-blind, 3-period crossover study. Each participant receives pregabalin once, with at least 48 hours washout between treatment periods.
Experimental: Sequence BCA (Naproxen - Placebo - Pregabalin); Participants assigned to this sequence will receive single-dose oral naproxen 550 mg in Period 1, matching placebo in Period 2, and pregabalin 300 mg in Period 3. Treatment periods are separated by at least 48 hours.	Drug: Placebo; Over-encapsulated matching placebo administered as a single oral dose in one treatment period of this randomized, double-blind, 3-period crossover study. The placebo is made to look identical to active study drug capsules to maintain blinding. Each participant receives placebo once, with at least 48 hours washout between treatment periods.; Drug: Naproxen; Over-encapsulated oral naproxen, 550 mg, administered as a single dose in one treatment period of this randomized, double-blind, 3-period crossover study. Each participant receives naproxen once, with at least 48 hours washout between treatment periods.; Drug: Pregabalin; Over-encapsulated oral pregabalin, 300 mg, administered as a single dose in one treatment period of this randomized, double-blind, 3-period crossover study. Each participant receives pregabalin once, with at least 48 hours washout between treatment periods.
Experimental: Sequence CAB (Placebo - Pregabalin - Naproxen); Participants assigned to this sequence will receive matching placebo in Period 1, pregabalin 300 mg in Period 2, and naproxen 550 mg in Period 3. Treatment periods are separated by at least 48 hours.	Drug: Placebo; Over-encapsulated matching placebo administered as a single oral dose in one treatment period of this randomized, double-blind, 3-period crossover study. The placebo is made to look identical to active study drug capsules to maintain blinding. Each participant receives placebo once, with at least 48 hours washout between treatment periods.; Drug: Naproxen; Over-encapsulated oral naproxen, 550 mg, administered as a single dose in one treatment period of this randomized, double-blind, 3-period crossover study. Each participant receives naproxen once, with at least 48 hours washout between treatment periods.; Drug: Pregabalin; Over-encapsulated oral pregabalin, 300 mg, administered as a single dose in one treatment period of this randomized, double-blind, 3-period crossover study. Each participant receives pregabalin once, with at least 48 hours washout between treatment periods.
Experimental: Sequence CBA (Placebo - Naproxen - Pregabalin); Participants assigned to this sequence will receive matching placebo in Period 1, naproxen 550 mg in Period 2, and pregabalin 300 mg in Period 3. Treatment periods are separated by at least 48 hours.	Drug: Placebo; Over-encapsulated matching placebo administered as a single oral dose in one treatment period of this randomized, double-blind, 3-period crossover study. The placebo is made to look identical to active study drug capsules to maintain blinding. Each participant receives placebo once, with at least 48 hours washout between treatment periods.; Drug: Naproxen; Over-encapsulated oral naproxen, 550 mg, administered as a single dose in one treatment period of this randomized, double-blind, 3-period crossover study. Each participant receives naproxen once, with at least 48 hours washout between treatment periods.; Drug: Pregabalin; Over-encapsulated oral pregabalin, 300 mg, administered as a single dose in one treatment period of this randomized, double-blind, 3-period crossover study. Each participant receives pregabalin once, with at least 48 hours washout between treatment periods.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change from baseline in pain intensity after cold pressor test	Change from baseline in participant-rated pain intensity VAS score measured immediately after hand removal from cold water during the cold pressor test (CPT). Higher scores indicate greater pain intensity.	Baseline and approximately 2, 5, and 8 hours after dosing in each treatment period
Change from baseline in pain intensity for allodynia (soft brush) after first heat/capsaicin pain model application	Change from baseline in participant-rated pain intensity VAS score for soft-brush allodynia at the heat/capsaicin pain model (HCM) site after the first HCM application. Higher scores indicate greater pain intensity.	Baseline and approximately 2, 5, and 8 hours after dosing in each treatment period
Change from baseline in pain intensity for hyperalgesia (pin-prick) after first heat/capsaicin pain model application	Change from baseline in participant-rated pain intensity VAS score for pin-prick hyperalgesia at the HCM site after the first HCM application. Higher scores indicate greater pain intensity.	Baseline and approximately 2, 5, and 8 hours after dosing in each treatment period
Change from baseline in pain intensity for mechanical hyperalgesia (pin-prick) at the UVB site	Change from baseline in participant-rated pain intensity VAS score for pin-prick hyperalgesia at the UVB-treated skin site. Higher scores indicate greater pain intensity.	Baseline and approximately 2, 5, and 8 hours after dosing in each treatment period
Change from baseline in pain intensity for thermal hyperalgesia (heat pain) at the UVB site	Change from baseline in participant-rated pain intensity VAS score for thermal-heat pain hyperalgesia at the UVB-treated skin site. Higher scores indicate greater pain intensity.	Baseline and approximately 2, 5, and 8 hours after dosing in each treatment period

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Weighted mean pain intensity VAS score for spontaneous pain over 0 to 60 minutes following first and second HCM applications	Weighted mean spontaneous pain visual analog scale (VAS) score calculated using area under the curve (AUC) over 60 minutes after each HCM application. Higher scores indicate greater spontaneous pain.	0 to 60 minutes after the first and second HCM applications during each treatment period
Area of secondary hyperalgesia to pin-prick following first and second HCM applications	Size of the mapped area of secondary pin-prick hyperalgesia at the HCM site after each HCM application. Larger area indicates greater secondary hyperalgesia.	After the first and second HCM applications during each treatment period
Change from baseline in pain intensity VAS score for thermal-heat hyperalgesia following first and second HCM applications	Change from baseline in participant-rated pain intensity VAS score for thermal-heat pain hyperalgesia at the HCM site after first and second HCM applications. Higher scores indicate greater pain intensity.	Baseline and approximately 2, 5, and 8 hours after dosing in each treatment period
Proportion of participants with at least 30% reduction from baseline in pain intensity VAS score after QST measures at HCM and UVB sites	Proportion of participants with at least 30% reduction from baseline in pain intensity VAS score after quantitative sensory testing (QST) modalities, including soft brush, light pressure, pin-prick, warm, heat pain, and cold, at HCM and UVB sites.	Baseline and approximately 2, 5, and 8 hours after dosing in each treatment period
Pharmacokinetic parameters of pregabalin and naproxen	Plasma pharmacokinetic parameters, including AUClast, Clast, Cmax, and Tmax, for pregabalin and naproxen.	Predose and 30, 90, 180, 240, 360, and 420 minutes after dosing in each active treatment period

Collaborators and Investigators

• Sponsor: National Center for Complementary and Integrative Health (NCCIH)
• Investigators: Principal Investigator: Miroslav Backonja, M.D., National Center for Complementary and Integrative Health (NCCIH)

Publications and helpful links

Helpful Links

• NIH Clinical Center Detailed Web Page

Study record dates

Study Major Dates

• Study Start (Estimated): June 15, 2026
• Primary Completion (Estimated): December 31, 2029
• Study Completion (Estimated): December 31, 2030

Study Registration Dates

• First Submitted: April 23, 2026
• First Submitted That Met QC Criteria: April 23, 2026
• First Posted (Actual): April 24, 2026

Study Record Updates

• Last Update Posted (Actual): April 24, 2026
• Last Update Submitted That Met QC Criteria: April 23, 2026
• Last Verified: April 20, 2026

More Information

Terms related to this study

• Keywords: Pain Mechanisms; Human Experimental Models of Pain; HCM (Heat/Capsaicin Pain Model)
• Additional Relevant MeSH Terms: Aortic Valve Disease; Pain; Neurologic Manifestations; Cardiovascular Diseases; Heart Diseases; Heart Valve Diseases; Cardiomyopathies; Aortic Stenosis, Subvalvular; Aortic Valve Stenosis; Pathological Conditions, Signs and Symptoms; Signs and Symptoms; Acute Pain; Cardiomyopathy, Hypertrophic; Amino Acids, Peptides, and Proteins; Organic Chemicals; Hydrocarbons; Hydrocarbons, Cyclic; Acids, Acyclic; Carboxylic Acids; Naphthalenes; Polycyclic Aromatic Hydrocarbons; Hydrocarbons, Aromatic; Polycyclic Compounds; Amino Acids; gamma-Aminobutyric Acid; Aminobutyrates; Butyrates; Naphthaleneacetic Acids; Pregabalin; Naproxen
• Other Study ID Numbers: 10002450; 002450-AT

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Plan Description: De-identified individual participant data underlying the results reported for this study may be shared upon request after completion of the primary endpoints. This may include baseline demographic and eligibility data, treatment sequence/assignment, pharmacodynamic data from the HEMP procedures and quantitative sensory testing (including VAS pain ratings from HCM, UVB, and cold pressor testing), pharmacokinetic concentration data and derived PK parameters, and safety data such as adverse events, vital signs, and clinical laboratory results. Data sharing will be handled by the PI or designee in accordance with NIH policies and applicable IRB/privacy requirements.
• IPD Sharing Time Frame: Individual participant data may be available after completion of the primary endpoints. Requests may be made to the PI or designee after primary endpoint completion and will be considered in accordance with NIH policy, IRB approval, and applicable privacy/confidentiality requirements.
• IPD Sharing Access Criteria: De-identified individual participant data may be shared with qualified researchers after completion of the primary endpoints by request to the PI or designee. Requests should describe the proposed research question and analysis plan. Access will be considered in accordance with NIH policies, IRB requirements, and applicable privacy and confidentiality protections. Data will be shared only in a form that protects participant identity, by a mechanism determined by the NIH study team at the time of approval.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No