An Early Phase 1 interventional study of Diclofenac and curcumin in Interaction, sponsored by Washington State University. Recruiting at 1 site in United States. Open to participants aged 18 Years to 65 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-10-20.
Sponsored by Washington State University · Early Phase 1, Interventional, and Basic science
The purpose of this pilot study is to gather preliminary data on the (1) contribution of the understudied drug metabolizing enzyme, UDP-glucuronosyltransferase (UGT) 2B17, to the metabolism of a widely used medication, diclofenac, and (2) impact of the UGT2B17 inhibitor and natural product, curcumin, on diclofenac pharmacokinetics. Results will inform future studies aimed to assess the effects of UGT2B17 genetic polymorphisms and co-consumed xenobiotics on the pharmacokinetics and toxicity risk of diclofenac and other UGT2B17 drug substrates.
Diclofenac, a widely used non-steroidal anti-inflammatory drug, has been linked to severe adverse effects such as gastrointestinal ulcers and bleeding and cardiotoxicity. Based on cardiotoxicity reports, US and European regulatory agencies withdrew over-the-counter (OTC) diclofenac, requiring the drug to be a prescription-only medication. However, diclofenac remains OTC in many countries, including Australia, China, and India, among others. Reported metabolic pathways of diclofenac in the liver are mediated by the prominent drug metabolizing enzyme, cytochrome P450 (CYP) 2C9, and the conjugative enzyme, UDP-glucuronosyltransferase (UGT) 2B7. However, recent in vitro and in silico data indicated that diclofenac is metabolized almost exclusively by a less-studied UGT, UGT2B17, in the intestine.
UGT2B17 is among the most genetically polymorphic enzymes, with highly prevalent copy number variations (CNVs). Individuals homozygous for the null allele, UGT2B17*2 (CNV=0), are considered poor metabolizers (PMs), whereas those homozygous for the reference allele, UGT2B17*1/*1 (CNV=2), are considered extensive metabolizers (EMs). Deletion of this gene may lead to large interindividual variability in the pharmacokinetics - and toxicity risk - for patients taking diclofenac and other UGT2B17 substrates, including vorinostat, MK7426, tamoxifen, exemestane, and testosterone. Collectively, considering UGT2B17 CNVs on the metabolism of these drugs is critical to ensure consistent and optimum safety, efficacy, and patient outcomes.
Recent preliminary data showed that curcumin, a principal curcuminoid of the natural product turmeric, is a potent inhibitor of UGT2B17. Turmeric is used worldwide and was the 2nd top-selling herbal supplement in the US in 2021, with nearly $100 million in total sales. Considering both turmeric/curcumin and diclofenac are used for arthritis and other inflammatory conditions, there is a high likelihood of patients co-consuming curcumin and diclofenac, raising concerns for variable diclofenac pharmacokinetics and toxicity risk.
The purpose of this pilot study is to gather preliminary data on the (1) contribution of UGT2B17 to diclofenac metabolism and (2) impact of curcumin co-administration on diclofenac pharmacokinetics. Results will inform future studies aimed to evaluate the effects of UGT2B17 genetic polymorphisms and co-consumed xenobiotics on the pharmacokinetics and toxicity risk of diclofenac and other UGT2B17 drug substrates.
Washington State University is the lead sponsor of 83 studies on the registry; 16 are open to participants now.
Of its 7 completed or terminated interventional studies of FDA-regulated products, 4 (57%) have results posted.
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Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Ways of preventing pregnancy. “Highly effective” methods fail less than 1% of the time a year when used correctly — for example an IUD or an implant.
Criteria usually say which methods count and how long to keep using them after the last dose, sometimes for male participants too. Some studies accept a partner’s vasectomy if it was confirmed successful and that person is the participant’s only sexual partner.
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Chronic obstructive pulmonary disease: long-term lung disease that makes it hard to breathe out, including emphysema and chronic bronchitis.
The human immunodeficiency virus, which weakens the immune system.
Many studies now accept people whose HIV is controlled on treatment, judged by the viral load and the CD4 count. Check the limits this study sets.
Contraception
Ways of preventing pregnancy. “Highly effective” methods fail less than 1% of the time a year when used correctly — for example an IUD or an implant.
Criteria usually say which methods count and how long to keep using them after the last dose, sometimes for male participants too. Some studies accept a partner’s vasectomy if it was confirmed successful and that person is the participant’s only sexual partner.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Informed consent
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
COPD
Chronic obstructive pulmonary disease: long-term lung disease that makes it hard to breathe out, including emphysema and chronic bronchitis.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
HIV
The human immunodeficiency virus, which weakens the immune system.
Many studies now accept people whose HIV is controlled on treatment, judged by the viral load and the CD4 count. Check the limits this study sets.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
A single dose of diclofenac (25 mg capsule) will be administered by mouth to 5 participants (minimum 2 females) genotyped as extensive metabolizers (Arm 1A) and 5 participants (minimum 2 females) genotyped as poor metabolizers (Arm 1B). Plasma and urine will be collected from 0-12 hours. A washout of at least 3 days will elapse between Arm 1 and Arm 2.
Drug: Diclofenac
A single oral dose of diclofenac (25 mg capsule) and a single oral dose of curcumin (2,000 mg tablet) will be administered by mouth to the 5 participants genotyped as extensive metabolizers. Plasma and urine will be collected from 0-12 hours.
Drug: Diclofenac · Dietary Supplement: curcumin
25 mg capsule
Also known as: Voltaren
2,000 mg tablet
Diclofenac area under the concentration vs. time curve (AUC) in UGT2B17 extensive metabolizers (EMs)
Diclofenac AUC in UGT2B17 EMs
Time frame: 0-12 hours
Diclofenac AUC in poor metabolizers (PMs)
Diclofenac AUC in UGT2B17 PMs
Time frame: 0-12 hours
Diclofenac AUC in EMs in the presence of curcumin
Diclofenac AUC in UGT2B17 EMs in the presence of curcumin
Time frame: 0-12 hours
Diclofenac maximum concentration (Cmax) in EMs
Diclofenac Cmax in UGT2B17 EMs
Time frame: 0-12 hours
Diclofenac Cmax in PMs
Diclofenac Cmax in UGT2B17 PMs
Time frame: 0-12 hours
Diclofenac Cmax in EMs in the presence of curcumin
Diclofenac Cmax in UGT2B17 EMs in the presence of curcumin
Time frame: 0-12 hours
Diclofenac renal clearance (CLr) in EMs
Diclofenac CLr in UGT2B17 EMs
Time frame: 0-12 hours
Diclofenac CLr in PMs
Diclofenac CLr in UGT2B17 PMs
Time frame: 0-12 hours
Diclofenac CLr in EMs in the presence of curcumin
Diclofenac CLr in UGT2B17 EMs in the presence of curcumin
Time frame: 0-12 hours
Diclofenac half-life (t1/2) in EMs
Diclofenac t1/2 in UGT2B17 EMs
Time frame: 0-12 hours
Diclofenac half-life (t1/2) in PMs
Diclofenac t1/2 in UGT2B17 PMs
Time frame: 0-12 hours
Diclofenac half-life (t1/2) in EMs in the presence of curcumin
Diclofenac t1/2 in UGT2B17 EMs in the presence of curcumin
Time frame: 0-12 hours
Plan to share: No
Started Mar 2024 (actual). Primary completion is estimated for Aug 2027, 41 months after the start.
Since we started tracking on Sep 25, 2026, the dates moved once, on Oct 20, 2026: primary completion Aug 2026 → Aug 2027 and completion Dec 2026 → Dec 2027.
Earlier changes are on the record history on ClinicalTrials.gov ↗
How these figures are worked out, and which studies are left out of them.
From the registry record's own update history. This site started tracking changes on Sep 25, 2026; for anything earlier, see the record history on ClinicalTrials.gov ↗
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Studies of the drug tested here: Diclofenac
Washington State University