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Session-Order Sensitivity of TS and OA in a Capsaicin Crossover Model (TS-OA-Cap)

3. juni 2026 opdateret af: John Srbely, University of Guelph

Session-order Sensitivity of Temporal Summation and Offset Analgesia in a Randomised Crossover Capsaicin Model of Secondary Hyperalgesia

Temporal summation (TS) and offset analgesia (OA) are widely used psychophysical endpoints in pain research that index different components of central nociceptive processing. While crossover designs are commonly used in experimental pain studies to reduce between-participant variability, the design-stability of these endpoints under repeated testing during experimental sensitisation is not well characterised. This study compared the design-stability of mechanical TS (Sumscore) and offset analgesia magnitude (OffA) in a two-period, vehicle-controlled crossover trial of capsaicin-evoked secondary hyperalgesia in healthy adults. The primary aim was methodological: to determine whether session-order effects differ between TS and OffA when these are used as outcome measures in two-period crossover designs of capsaicin-induced central sensitisation. Topical capsaicin was used as a reversible experimental intervention to create a controlled, transient state of secondary hyperalgesia rather than as a therapeutic intervention. The study informs endpoint selection in future quantitative sensory testing (QST) crossover trials.

Studieoversigt

Status

Afsluttet

Betingelser

Intervention / Behandling

Detaljeret beskrivelse

This was a single-site, two-period, vehicle-controlled, allocation- and formulation-blinded, randomised crossover study conducted at the Department of Human Health Science, University of Guelph, Canada. Sixteen healthy adult volunteers (10 female, 6 male; mean age 21.9 years) were recruited between May 2024 and April 2025. Participants were randomised in a 1:1 intended allocation to one of two sequences: capsaicin-first then vehicle (Sequence A-to-B) or vehicle-first then capsaicin (Sequence B-to-A); actual allocation was 6:10. The allocation sequence was computer-generated by a research assistant not involved in outcome collection. Sessions were separated by a minimum 1-week washout. Topical 0.075% capsaicin cream (Zostrix; Hi-Tech Pharmacal) was applied as a 5 mL dose to a 5 x 10 cm target area on the lateral elbow and to bilateral C5-C6 cervicothoracic dermatomes. The comparator was an equivalent 5 mL volume of inert vehicle lotion (Lubriderm; Johnson & Johnson) applied identically; creams were matched for colour and texture and prepared by a research assistant in unlabelled containers. Mechanical temporal summation (Sumscore; 256 mN pinprick, 16 stimuli at 1 Hz) and thermal offset analgesia (OA; 32-46°C stepped-stimulus protocol with three thermal hold durations of 5, 10, and 15 s) were assessed at baseline and at 10, 20, 30, and 40 min post-intervention. Continuous pain ratings during thermal stimulation were captured via CoVAS. Primary outcomes (Sumscore and the duration-averaged baseline-normalised OffA) were analysed using REML linear mixed-effects models with fixed effects for Intervention, Time, Intervention x Time, Period, and Sequence, with random intercepts for Participant; sex was included as a pre-specified covariate. Within-session temporal stability was assessed using ICC(2,1). A combined Measure x Intervention x Period model tested for differential design-sensitivity between TS and OffA. The study was approved by the University of Guelph Research Ethics Board (REB #19-06-003).

Undersøgelsestype

Interventionel

Tilmelding (Faktiske)

16

Fase

  • Ikke anvendelig

Kontakter og lokationer

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Studiesteder

  • Canada
    • Ontario
      • Guelph, Ontario, Canada, N1G2W1
        • Human Health Sciences, University of Guelph

Deltagelseskriterier

Forskere leder efter personer, der passer til en bestemt beskrivelse, kaldet berettigelseskriterier. Nogle eksempler på disse kriterier er en persons generelle helbredstilstand eller tidligere behandlinger.

Berettigelseskriterier

Aldre berettiget til at studere

  • Voksen
  • Ældre voksen

Tager imod sunde frivillige

Ja

Beskrivelse

Inclusion Criteria:

  • Healthy adult volunteers (≥18 years of age)
  • Able to provide written informed consent in English

Exclusion Criteria:

  • Current or chronic pain
  • Neurological disease
  • Skin conditions or sensitivity over the test sites to capsaicin
  • Contraindications to thermal stimulation of the skin
  • Musculoskeletal conditions that could alter somatosensory processing
  • Use of analgesic medications within 24 hours prior to each session
  • Use of caffeine within 24 hours prior to each session
  • Use of alcohol within 24 hours prior to each session

Studieplan

Dette afsnit indeholder detaljer om studieplanen, herunder hvordan undersøgelsen er designet, og hvad undersøgelsen måler.

Hvordan er undersøgelsen tilrettelagt?

Design detaljer

  • Primært formål: Grundvidenskab
  • Tildeling: Randomiseret
  • Interventionel model: Crossover opgave
  • Maskning: Tredobbelt

Våben og indgreb

Deltagergruppe / Arm
Intervention / Behandling
Eksperimentel: Arm 1: Sequence A-to-B (Capsaicin first)
Participants received topical 0.075% capsaicin (Zostrix) cream (5 mL) in Period 1, followed by topical inert (Lubriderm) vehicle (5 mL) in Period 2. Periods were separated by a minimum 1-week washout. n = 6.
Medicin: Topical 0.075% capsaicin cream (Zostrix)
5 mL of 0.075% capsaicin cream (Zostrix; Hi-Tech Pharmacal, Amityville, NY, USA) applied to a 5 x 10 cm target region on the lateral elbow and to bilateral C5-C6 cervicothoracic dermatomes (total 15 mL). The cream was massaged into the skin by a gloved investigator until no residue was visible. Used as an experimental probe to evoke transient, reversible secondary hyperalgesia; not under therapeutic evaluation.
Andet: Topical vehicle lotion (Lubriderm)
5 mL of inert vehicle lotion (Lubriderm; Johnson & Johnson, Montgomery, NJ, USA) applied to the same dermatomes as the capsaicin condition (total 15 mL), using the identical preparation and massage technique. Matched to the capsaicin cream for colour and texture.
Aktiv komparator: Arm 2: Sequence B-to-A (Vehicle first)
Participants received topical inert (Lubriderm) vehicle (5 mL) in Period 1, followed by topical 0.075% capsaicin (Zostrix) cream (5 mL) in Period 2. Periods were separated by a minimum 1-week washout. n = 10.
Medicin: Topical 0.075% capsaicin cream (Zostrix)
5 mL of 0.075% capsaicin cream (Zostrix; Hi-Tech Pharmacal, Amityville, NY, USA) applied to a 5 x 10 cm target region on the lateral elbow and to bilateral C5-C6 cervicothoracic dermatomes (total 15 mL). The cream was massaged into the skin by a gloved investigator until no residue was visible. Used as an experimental probe to evoke transient, reversible secondary hyperalgesia; not under therapeutic evaluation.
Andet: Topical vehicle lotion (Lubriderm)
5 mL of inert vehicle lotion (Lubriderm; Johnson & Johnson, Montgomery, NJ, USA) applied to the same dermatomes as the capsaicin condition (total 15 mL), using the identical preparation and massage technique. Matched to the capsaicin cream for colour and texture.

Hvad måler undersøgelsen?

Primære resultatmål

Resultatmål
Foranstaltningsbeskrivelse
Tidsramme
Mechanical temporal summation (Sumscore)
Tidsramme: Baseline and 10, 20, 30, and 40 min post-intervention (within each of two sessions, separated by a minimum 1-week washout)
Sumscore is a summed pinprick temporal-summation response computed from a train of 16 repeated 256 mN pinprick stimuli delivered perpendicularly to the skin at 1 Hz, paced by a metronome. Pain ratings (NPRS 0-10) immediately after each stimulus were summed (Clouse et al., 2021). The primary Sumscore endpoint was pre-specified as the average of the lateral and inferior testing sites at the lateral elbow, expressed as a baseline-normalised ratio.
Baseline and 10, 20, 30, and 40 min post-intervention (within each of two sessions, separated by a minimum 1-week washout)
Offset analgesia magnitude (OffA)
Tidsramme: Baseline and 10, 20, 30, and 40 min post-intervention (within each of two sessions, separated by a minimum 1-week washout)
OffA was measured during a three-phase stepped-stimulus thermal protocol (32-45-46-45-32°C; T1/T2/T3 phases) using a 32 x 32 mm Peltier contact thermode (TSA-II NeuroSensory Analyzer, Medoc AMS). Continuous pain ratings were collected via CoVAS (0-100) at 10 Hz. OA magnitude was quantified as peak minus nadir CoVAS during the 46°C hold and the subsequent 45°C phase. The primary OffA endpoint was pre-specified as the duration-averaged value across three thermal hold durations (5, 10, and 15 s at 46°C), expressed as a baseline-normalised ratio.
Baseline and 10, 20, 30, and 40 min post-intervention (within each of two sessions, separated by a minimum 1-week washout)

Sekundære resultatmål

Resultatmål
Foranstaltningsbeskrivelse
Tidsramme
Within-session temporal stability (ICC(2,1)) of Sumscore and OffA
Tidsramme: 10, 20, 30, and 40 minutes post-intervention
Intraclass correlation coefficient (ICC(2,1); Shrout and Fleiss, 1979) computed across the four post-intervention time points (10, 20, 30, 40 min) within each intervention condition, separately for Sumscore and OffA. Reported with bias-corrected bootstrap 95% confidence intervals.
10, 20, 30, and 40 minutes post-intervention
Differential design-sensitivity (Measure × Intervention × Period interaction)
Tidsramme: 10, 20, 30, and 40 minutes post-intervention, across two crossover periods separated by a minimum 1-week washout.
A combined linear mixed-effects model using within-measure z-scored outcomes tested whether the period-adjusted intervention estimate differed between TS and OffA. Three-way Measure x Intervention x Period interaction tested via Wald F-tests with residual degrees of freedom.
10, 20, 30, and 40 minutes post-intervention, across two crossover periods separated by a minimum 1-week washout.

Samarbejdspartnere og efterforskere

Det er her, du vil finde personer og organisationer, der er involveret i denne undersøgelse.

Sponsor

University of Guelph

Publikationer og nyttige links

Den person, der er ansvarlig for at indtaste oplysninger om undersøgelsen, leverer frivilligt disse publikationer. Disse kan handle om alt relateret til undersøgelsen.

Generelle publikationer

Datoer for undersøgelser

Disse datoer sporer fremskridtene for indsendelser af undersøgelsesrekord og resumeresultater til ClinicalTrials.gov. Studieregistreringer og rapporterede resultater gennemgås af National Library of Medicine (NLM) for at sikre, at de opfylder specifikke kvalitetskontrolstandarder, før de offentliggøres på den offentlige hjemmeside.

Studer store datoer

Studiestart (Faktiske)

1. maj 2024

Primær færdiggørelse (Faktiske)

30. april 2025

Studieafslutning (Faktiske)

30. april 2025

Datoer for studieregistrering

Først indsendt

22. maj 2026

Først indsendt, der opfyldte QC-kriterier

3. juni 2026

Først opslået (Faktiske)

4. juni 2026

Opdateringer af undersøgelsesjournaler

Sidste opdatering sendt (Faktiske)

4. juni 2026

Sidste opdatering indsendt, der opfyldte kvalitetskontrolkriterier

3. juni 2026

Sidst verificeret

1. juni 2026

Mere information

Begreber relateret til denne undersøgelse

Nøgleord

Yderligere relevante MeSH-vilkår

Andre undersøgelses-id-numre

  • GUELPH-REB-19-06-003
  • REB #19-06-003 (Anden identifikator: University of Guelph)

Plan for individuelle deltagerdata (IPD)

Planlægger du at dele individuelle deltagerdata (IPD)?

JA

IPD-planbeskrivelse

De-identified individual participant data (IPD) and statistical analysis code will be available from the corresponding author on reasonable request, subject to a data-use agreement and institutional ethics/data-sharing requirements. Materials required to reproduce the intervention and assessment protocol are described in the published Methods and Supplementary Materials.

IPD-delingstidsramme

On request following publication of the primary manuscript.

IPD-delingsadgangskriterier

Reasonable request to the corresponding author for non-commercial research use, subject to a data-use agreement consistent with University of Guelph data-sharing policy.

IPD-deling Understøttende informationstype

  • STUDY_PROTOCOL
  • SAP
  • ICF
  • ANALYTIC_CODE

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Kliniske forsøg med Topical 0.075% capsaicin cream (Zostrix)

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