Novel Use of Probenecid to Alleviate Symptoms of Opioid Withdrawal

Phase 2

Recruiting

• Conditions: Chronic Pain; Drug Dependence of Morphine Type; Symptom, Withdrawal
• Interventions: Drug: Probenecid

• Registration Number: NCT04939623
• Lead Sponsor: University of Calgary

Brief Summary

The proposed clinical trial will address the problem of opioid withdrawal. Opioids are essential for pain-relief in the short term, but their continued use is associated with a host of adverse effects. People living with chronic pain who were initiated on opioid therapy now find themselves with a major life-changing problem - dependence on opioid medications. Opioid withdrawal symptoms are a key barrier to decreasing or stopping their opioid medication. Currently, there are few medications that ameliorate the symptoms of opioid withdrawal. This problem is a major part of the opioid crisis in Canada, and impacts people across all demographics and socioeconomic status. A misconception is that only individuals with opioid use disorder are susceptible to opioid withdrawal; on the contrary, appropriate use of prescription opioids to manage pain can lead to significant symptoms of opioid withdrawal when it is reduced or stopped. Patients in Alberta who are at risk for opioid withdrawal, either from prescribed use or misuse will be primarily impacted by this trial.

The investigators have recently explored the underlying causes of opioid withdrawal and identified an important target in the spinal cord that is responsible for producing withdrawal symptoms in rats and mice. The target, a protein called pannexin-1 (Panx1), is located throughout the body, specifically in the brain and spinal cord. Using sophisticated biochemical, genetic, and pharmacological techniques, the investigators demonstrated how Panx1 on immune cells is implicated in the production of opioid withdrawal symptoms after cessation of fentanyl and morphine in opioid dependent rodents. The investigators then attenuated these symptoms of withdrawal using probenecid, a drug which inherently blocks Panx1 activity. Because probenecid is a safe and clinically available drug, the findings could be immediately translated into clinical therapy to support people who are struggling with the symptoms of opioid withdrawal and provide clinicians with a safe and effective option for caring for this population.

Detailed Description

The proposed clinical trial will address the problem of opioid withdrawal. Opioids are essential for pain-relief in the short term, but their continued use is associated with a host of adverse effects. People living with chronic pain who were initiated on opioid therapy now find themselves with a major life-changing problem - dependence on opioid medications. Opioid withdrawal symptoms are a key barrier to decreasing or stopping their opioid medication. Currently, there are few medications that ameliorate the symptoms of opioid withdrawal. This problem is a major part of the opioid crisis in Canada, and impacts people across all demographics and socioeconomic status. A misconception is that only individuals with opioid use disorder are susceptible to opioid withdrawal; on the contrary, appropriate use of prescription opioids to manage pain can lead to significant symptoms of opioid withdrawal when it is reduced or stopped. Patients in Alberta who are at risk for opioid withdrawal, either from prescribed use or misuse will be primarily impacted by this trial.

Our team has recently explored the underlying causes of opioid withdrawal and identified an important target in the spinal cord that is responsible for producing withdrawal symptoms in rats and mice. The target, a protein called pannexin-1 (Panx1), is located throughout the body, specifically in the brain and spinal cord. Using sophisticated biochemical, genetic, and pharmacological techniques, the investigators demonstrated how Panx1 on immune cells is implicated in the production of opioid withdrawal symptoms after cessation of fentanyl and morphine in opioid dependent rodents. The investigators then attenuated these symptoms of withdrawal using probenecid, a drug which inherently blocks Panx1 activity. Because probenecid is a safe and clinically available drug, the findings could be immediately translated into clinical therapy to support people who are struggling with the symptoms of opioid withdrawal and provide clinicians with a safe and effective option for caring for this population.

Probenecid was initially developed in the early 1950s as a tool to enhance the activity of penicillin and allow for outpatient treatment of various infections. It increases plasma levels and the half-life of weak organic acids (penicillins, cephalosporins, or other beta-lactam antibiotics) by competitively inhibiting their renal tubular secretion. As a result, it became widely used in combination with beta-lactam antibacterial agents. It is still occasionally used today in combination with cefazolin for the treatment of skin and soft tissue infections, and in combination with cefoxitin or doxycycline as an option for outpatient treatment of pelvic inflammatory disease.

Probenacid also competitively inhibits active reabsorption of uric acid at the level of the proximal convoluted tubule promoting excretion of uric acid, thereby reducing serum urate concentrations.

Probenecid is also used in combination with cidofovir for the prevention of cidofovir-related nephrotoxicity when used to treat cytomegalovirus retinitis in patients with HIV. More recently, the effects of probenecid on serotonin levels and TRPV2 channels has led to speculation about its utility in depression, Parkinson's Disease, and congestive heart failure.

The drug is no longer commercially available in Canada but is commercially available as 500 mg tablets in the United States which can be acquired through Health Canada's Special Access Program. Probenecid can, however, be prepared in Canada by compounding pharmacies.

The study is a single centre, randomized, double blind, placebo-controlled, 12-week clinical trial meant to study probenecid use among adult participants living with chronic non-cancer pain using opioid drug therapy on a daily basis and planning to voluntarily reduce their dose.

Study Timeline

• Study First Submitted: 2020-09-11
• Study First Submitted QC: 2021-06-22
• Study First Posted: 2021-06-25
• Study Start: 2023-10-31
• Status Verified: 2024-12
• Last Update Submitted: 2025-03-25
• Last Update Posted: 2025-03-30
• Primary Completion: 2025-12-31
• Study Completion: 2025-12-31

Recruitment & Eligibility

• Status: RECRUITING
• Sex: All
• Target Recruitment: 40

Inclusion Criteria

1. Adults with chronic pain. Age greater than or equal to 18 years on the day of enrolment.
2. Subjects are currently taking a daily opioid pain medication and planning to taper the dose.
3. Participants complete at least one voluntary opioid dose reduction in the twelve-week study period.
4. Glomerular filtration rate (GFR) > 50 mL/min
5. Capable of providing informed consent

Exclusion Criteria

1. Allergy to probenecid or related drugs

2. History of uric acid renal calculi, if known to be urate calculi. If unknown type, then any history of renal calculi.

3. Known G6PD deficiency

4. Active gout in any joint

5. Current use of drugs whose exposure may be prolonged, or risk of toxicity increased when used in combination with probenecid:

   1. Penicillins, specifically ampicillin, penicillin G sodium, and piperacillin
   2. Carbapenems, specifically doripenem and meropenem
   3. Lorazepam, midazolam, nitrazepam
   4. Ketorolac
   5. Oseltamivir
   6. Methotrexate
   7. Mycophenolate

6. Current use of drugs which may mask symptoms of withdrawal:

   a. Clonidine, lofexidine, tizanidine

7. Current use of drugs which may diminish the effect of probenecid:

   a. High dose salicylates including greater than 325 mg PO daily of acetylsalicylic acid (ASA)

8. Pregnancy or breastfeeding

9. Any major comorbid medical condition which might impair follow-up or result in a safety risk to the participant

10. Participation in another clinical trial investigating a drug, medical device, or a medical procedure during the 30 days prior to enrolment.

Study & Design

• Study Type: INTERVENTIONAL
• Study Design: PARALLEL

Arm && Interventions

Group	Intervention	Description
Probenecid 500 mg PO BID	Probenecid	Probenecid 500 mg X 1 PO BID and Placebo X 1 PO BID
Probenecid 1000 mg PO BID	Probenecid	Probenecid 500mg X 2 PO BID
Placebo PO BID	Probenecid	Placebo X 2 PO BID

Primary Outcome Measures

Name	Time	Method
To evaluate tolerability of oral probenecid in patients undergoing voluntary opioid tapering	12 weeks	Tolerability will be assessed through use of the "SAFTEE-SI questionnaire recorded as a percentage for each of the three group assignments and again in two groups titled "probenecid" and "placebo".; Statistical comparisons will be made between groups with regard to the percentage of participants experiencing any given adverse event. (example: rash occurred at a rate of 0% with placebo, 2% with probenecid 500 mg, and 4% with probenecid 1000 mg). Comparisons will also be made between the "probenecid group" and "placebo group" (Example: Blurred vision occurred at a rate of 2% with placebo compared to 4% with probenecid)
To evaluate acceptability of oral probenecid in patients undergoing voluntary opioid tapering	12 weeks	Acceptability will be measured by assessing the Percent of patients achieving 80% compliance in each group as measured by returned supply in medication vials.
To evaluate safety of oral probenecid in patients undergoing voluntary	12 weeks	Safety will be assessed by the clinical research team who have diagnosed the adverse events which will be recorded as a percentage for each of the three group assignments and again in two groups titled "probenecid" and "placebo".; Statistical comparisons will be made between groups with regard to the percentage of participants experiencing any given adverse event. (example: rash occurred at a rate of 0% with placebo, 2% with probenecid 500 mg, and 4% with probenecid 1000 mg). Comparisons will also be made between the "probenecid group" and "placebo group" (Example: Blurred vision occurred at a rate of 2% with placebo compared to 4% with probenecid)

Secondary Outcome Measures

Name	Time	Method
To evaluate the feasibility of treatment with probenecid in a patient-directed opioid tapering protocol, in the setting of an interdisciplinary pain clinic	3 years	To evaluate the feasibility of treatment with probenecid in a patient-directed opioid tapering protocol, in the setting of an interdisciplinary pain clinic. The sample size of enrolling 40 subjects over a 3 year period will be be used to evaluate the feasibility of a larger study using a similar protocol.
To evaluate whether Panx1 gene variants correlate with opioid withdrawal severity and response to probenecid by collecting salivary samples and performing DNA extraction in a small cohort.	3 years	A summary of association analyses between subjects DNA samples will be evaluated to determine PANX1 genetic variants and then analyzed for corellation with the study endpoints (e.g. adverse events, opioid withdrawal) and then be reported by treatment group.

Trial Locations

Locations (1)

Richmond Road Diagnostic and Treatment Centre; 🇨🇦 Calgary, Alberta, Canada