NCT04603066

Tariquidar-ondansetron Combination in Neuropathic Pain

Completed Phase 1, PHASE2 Results posted Last updated 14 August 2025

What this trial tests

Phase 1, PHASE2 trial testing Ondansetron 16 mg with Tariquidar in Neuropathic Pain in 24 participants. Completed in 3 November 2023.

Timeline

31 January 2021

Primary endpoint
21 October 2023

3 November 2023

Quick facts

Lead sponsor	Washington University School of Medicine
Phase	Phase 1, PHASE2
Status	Completed
Study type	INTERVENTIONAL
Allocation	randomized
Design	crossover
Masking	triple
Primary purpose	treatment
Enrollment	24
Start date	31 January 2021
Primary completion	21 October 2023
Estimated completion	3 November 2023
Sites	1 location across United States

Drugs / interventions tested

• Ondansetron 16 mg with Tariquidar — full drug profile →
• Ondansetron 16 mg with Placebo — full drug profile →

Conditions studied

• Neuropathic Pain — all drugs for Neuropathic Pain →

Sponsor

Washington University School of Medicine

Who can join

Adults 18 to 65, any sex, with Neuropathic Pain. Patients with the condition only — healthy volunteers not accepted.

Results — posted to ClinicalTrials.gov

Per-arm endpoint measurements with 95% confidence intervals where reported. Source: trial results section.

Concertation-time Profile of Ondansetron in Plasma, Measured by the Area Under the Concentration-time Curve (AUC) Primary · Measurements over 240 minutes, extrapolated to infinity

AUCinf for Ondansetron concentration in plasma based on venous blood sampling for plasma concentrations of ondansetron obtained at 0, 15, 30, 60, 90, 120, 180, and 240 minutes from the beginning of ondansetron infusion.

Group	Value	95% CI
Ondansetron + Tariquidar	0.89	± 0.29
Ondansetron + Placebo	0.87	± 0.45

Cerebrospinal Fluid to Plasma Concentration Ratio of Ondansetron Primary · anytime between 0-240 minutes

The level of ondansetron in plasma and CSF (cerebrospinal fluid) in samples, taken around the same time, was measured, and the ratio of the two values was calculated. This ratio (partition coefficient, Kp) of ondansetron, compared between the two sessions, with placebo vs tariquidar

Group	Value	95% CI
Ondansetron + Tariquidar	0.132	± 0.017
Ondansetron + Placebo	0.112	± 0.018

% Change in Pain Intensity Secondary · baseline to 90 minutes after ondansetron IV infusion

Change in spontaneous pain intensity (measured on a 0-10 numerical rating scale; 0=no pain, 10=worst imaginable pain) from baseline to 90 minutes after ondansetron IV infusion, compared between two sessions with and without tariquidar. Values are presented as a percentage change from baseline.

Group	Value	95% CI
Ondansetron + Tariquidar	37.2	± 35.1
Ondansetron + Placebo	28.8	± 28.7

Conditioned Pain Modulation (CPM) Magnitude (ΔCPM) Secondary · Baseline and 90 minutes after the end of ondansetron infusion

Conditioned Pain Modulation (CPM) is a psychophysical test to assess the efficiency of descending pain inhibition. CPM is calculated as difference in heat pain threshold with and without pain conditioning - i.e. immersion of a hand in cold water. Conditioned Pain Modulation (CPM) Negative CPM values represent efficient pain modulation/inhibition. This test was administered at baseline, and again 90-min after the end of ondansetron infusion. CPM values can range from -100 to 100, CPM\<0 (i.e. decreased pain to heat stimulus following conditioning) implies descending pain inhibition. CPM Magni

Group	Value	95% CI
Ondansetron + Tariquidar	0.1	± 8.2
Ondansetron + Placebo	1.8	± 10.4

Correlation Between CPM Magnitude (ΔCPM) and Change in Pain Intensity Secondary · 0-240 min from infusion

The association between baseline Conditioned Pain Modulation (CPM) magnitude (ΔCPM) and the % pain reduction from baseline will be determined by bivariate regression.

Group	Value	95% CI
Ondansetron + Tariquidar	0.02
Ondansetron + Placebo	0.01

Change in Neuropathic Pain Symptom Inventory (NPSI) Score Secondary · baseline to 70 min after infusion

Changes in the Neuropathic Pain Symptom Inventory (NPSI) total score will be compared between treatment sessions. NPSI is a questionnaire used to assess and quantify neuropathic pain by asking patients to rate the severity of different pain sensations on a scale of 0 to 10, with 0 being no pain and 10 being the worst pain imaginable. The version administered in the study consists of seven questions, each rated on a scale from 0 to 10, with the total score being the sum of all ratings. The possible range of the NPSI score of the version administered in the study is 70, and, since we measure t

Group	Value	95% CI
Ondansetron + Tariquidar	-8.6	± 7.0
Ondansetron + Placebo	-13.2	± 7.1

Adverse events — posted to ClinicalTrials.gov

Time frame: 6 weeks. Reporting threshold: 4%. Adverse-event reports describe events observed during the trial — not all are caused by the drug.

Ondansetron + Tariquidar

Serious: 0/23 (0%)

Deaths: 0/23

Ondansetron + Placebo

Serious: 0/24 (0%)

Deaths: 0/24

Other adverse events (10 terms — click to expand)

Reaction	System	Ondansetron + Tariquidar	Ondansetron + Placebo
Metallic Taste	Gastrointestinal disorders	—	—
Infusion site bruising	Skin and subcutaneous tissue disorders	—	—
Headache	Nervous system disorders	—	—
Drowsiness	Nervous system disorders	—	—
Nausea	Nervous system disorders	—	—
Syncope	Nervous system disorders	—	—
Constipation	Gastrointestinal disorders	—	—
Dry Mouth	Gastrointestinal disorders	—	—
Paraesthesia	Nervous system disorders	—	—
Dizziness	Nervous system disorders	—	—

Data from ClinicalTrials.gov NCT04603066 adverse events section.

Sponsor's own description

Prospective, randomized, double-blind, placebo controlled, cross-over proof of concept study.

To determine the pharmacokinetics and tolerability of co-administration of 5-HT3R antagonist ondansetron with a P-glycoprotein inhibitor tariquidar, in patients with neuropathic pain.

Publications & conference data

No peer-reviewed publications indexed yet for this trial. Completed trials usually publish results within 12-18 months.