A Phase 2 interventional study of THB335 Lower Dose and THB335 Higher Dose in Chronic Spontaneous Urticaria (CSU) and Chronic Idiopathic Urticaria, sponsored by Calixis Inc.. Recruiting at 15 sites in United States. Open to participants aged 18 Years to 85 Years. Per ClinicalTrials.gov, last updated 2026-11-02.
Sponsored by Calixis Inc. · Phase 2, Interventional, and Treatment
THB335-201 is a Phase 2, randomized, double-blind, placebo-controlled, parallel-group, multicenter study in adults with CSU who remain symptomatic despite standard-of-care treatment. The study includes a Screening Period of up to 4 weeks, a 12-week Treatment Period, and a 4-week Follow-Up Period, for a total participant duration of approximately 20 weeks.
This study will evaluate the efficacy and safety of THB335 in adults with chronic spontaneous urticaria (CSU) who continue to have hives and itching despite treatment with a second-generation H1 antihistamine. Approximately 81 participants will be randomly assigned to receive 1 of 2 doses of THB335 or matching placebo orally once daily for 12 weeks, in addition to their stable antihistamine treatment. Neither participants nor study personnel will know the assigned treatment. Participants will then be followed for 4 weeks. The main assessment is the change in weekly Urticaria Activity Score (UAS7) from baseline to Week 12.
This study will have approximately 40 locations.
194 studies on the registry are indexed under Chronic Urticaria; 46 are open to participants now.
This study's planned enrollment of 81 is close to the median of 80 across 145 interventional studies indexed under Chronic Urticaria.
Browse Chronic Urticaria studies →This is the only study on the registry with Calixis Inc. as lead sponsor.
Counted across the registry records on this site, refreshed daily.
Key Inclusion Criteria:
Key Exclusion Criteria:
Additional eligibility criteria are outlined in the full protocol. The study investigator will review all requirements with potential participants to determine whether they are eligible to participate.
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.
Weight in kilograms divided by height in metres squared. Example: 70 kg and 1.75 m gives 70 ÷ (1.75 × 1.75) ≈ 22.9.
What counts as overweight or obesity differs between countries (some use lower cut-offs), so go by the range the study states.
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.
A weakened immune system. It can come from an illness, such as HIV or some blood cancers, or from medicines that turn the immune system down, for example after an organ transplant or for an autoimmune disease; steroids at higher doses count.
Read whether the line is about a condition or about medicines, and which medicines and doses it means.
A drug or device being studied in a clinical trial.
It may be new, or already approved and being studied for another use, dose or form. Criteria often leave out people who took part in another study of one within a recent period, commonly 30 days or five half-lives.
Judged by the study doctor to matter for your health or for the study. It is a doctor’s decision, so ask the study team if you are unsure whether something counts.
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.
A recording of the heart’s electrical activity, taken with stickers on the chest, arms and legs. It takes a few minutes and does not hurt.
On an ECG, the QT interval is the time the heart’s lower chambers take to activate electrically and recover in each beat. QTc is that time adjusted for heart rate (QTcF by Fridericia’s formula, QTcB by Bazett’s). Some medicines lengthen it, and a long QTc can raise the risk of a dangerous heart rhythm.
The study may name a correction formula and a limit in milliseconds, often around 450–480.
An allergy, or another reaction of the immune system, to a substance. “Hypersensitivity to the study drug” means a known allergic reaction to it — not every side effect a medicine can have.
Malignancy means cancer. Criteria about another or earlier malignancy ask whether you have had a different cancer, usually within a set number of years.
Some are commonly allowed, such as treated skin cancers other than melanoma and early cancers removed completely — check the exceptions this study lists.
BMI (body mass index)
Weight in kilograms divided by height in metres squared. Example: 70 kg and 1.75 m gives 70 ÷ (1.75 × 1.75) ≈ 22.9.
What counts as overweight or obesity differs between countries (some use lower cut-offs), so go by the range the study states.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
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.
Immunosuppression
A weakened immune system. It can come from an illness, such as HIV or some blood cancers, or from medicines that turn the immune system down, for example after an organ transplant or for an autoimmune disease; steroids at higher doses count.
Read whether the line is about a condition or about medicines, and which medicines and doses it means.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Investigational drug or device
A drug or device being studied in a clinical trial.
It may be new, or already approved and being studied for another use, dose or form. Criteria often leave out people who took part in another study of one within a recent period, commonly 30 days or five half-lives.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Clinically significant
Judged by the study doctor to matter for your health or for the study. It is a doctor’s decision, so ask the study team if you are unsure whether something counts.
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.
ECG (electrocardiogram)
A recording of the heart’s electrical activity, taken with stickers on the chest, arms and legs. It takes a few minutes and does not hurt.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
QT and QTc
On an ECG, the QT interval is the time the heart’s lower chambers take to activate electrically and recover in each beat. QTc is that time adjusted for heart rate (QTcF by Fridericia’s formula, QTcB by Bazett’s). Some medicines lengthen it, and a long QTc can raise the risk of a dangerous heart rhythm.
The study may name a correction formula and a limit in milliseconds, often around 450–480.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Hypersensitivity
An allergy, or another reaction of the immune system, to a substance. “Hypersensitivity to the study drug” means a known allergic reaction to it — not every side effect a medicine can have.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Cancer (malignancy)
Malignancy means cancer. Criteria about another or earlier malignancy ask whether you have had a different cancer, usually within a set number of years.
Some are commonly allowed, such as treated skin cancers other than melanoma and early cancers removed completely — check the exceptions this study lists.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Orally-administered THB335 higher dose.
Drug: THB335 Higher Dose
Orally-administered THB335 lower dose.
Drug: THB335 Lower Dose
Orally-administered matching placebo.
Drug: Placebo
THB335 is an orally administered capsule added to a stable background regimen of a second generation H1 antihistamine.
THB335 is an orally administered capsule added to a stable background regimen of a second generation H1 antihistamine.
Placebo is an orally administered capsule added to a stable background regimen of a second generation H1 antihistamine.
Change From Baseline in Weekly Urticaria Activity Score (UAS7) at Week 12
UAS7 is the sum of daily Urticaria Activity Scores over 7 days. The daily score combines the Hives Severity Score and Itch Severity Score, each scored from 0 to 3. UAS7 ranges from 0 to 42; higher scores indicate greater disease activity.
Time frame: Baseline and Week 12
Percentage of Participants With UAS7 ≤ 6
UAS7 ranges from 0 to 42. UAS7 ≤ 6 represents well-controlled urticaria.
Time frame: Through Week 12
Percentage of Participants With UAS7 = 0
UAS7 = 0 indicates no reported hives or itching during the 7-day scoring period.
Time frame: Week 12
Change From Baseline in UAS7
UAS7 ranges from 0 to 42.
Time frame: Baseline to Week 8
Change From Baseline in Weekly Itch Severity Score (ISS7)
ISS7 is the sum of daily itch-severity scores over 7 days. Daily itch severity is scored from 0 (no itch) to 3 (severe itch); ISS7 ranges from 0 to 21.
Time frame: Baseline to Week 12
Change From Baseline in Weekly Hives Severity Score (HSS7)
HSS7 is the sum of daily hives-severity scores over 7 days. Daily hives severity is scored from 0 (no hives) to 3 (many hives); HSS7 ranges from 0 to 21.
Time frame: Baseline to Week 12
Change From Baseline in Urticaria Control Test (UCT) Score
The UCT contains 4 questions scored from 0 to 4. Total scores range from 0 to 16.
Time frame: Baseline and Week 12
Incidence and Severity of Treatment-Emergent Adverse Events (TEAEs) and Serious Adverse Events (SAEs)
Number and percentage of participants with TEAEs, treatment-related TEAEs, SAEs, AEs leading to discontinuation, and AEs by severity.
Time frame: Through Week 16
Number of Participants With Clinically Significant Changes in Vital Signs
Clinically significant changes or abnormalities in blood pressure, heart rate, respiratory rate, pulse oximetry, and body temperature will be assessed.
Time frame: Through Week 16
Number of Participants With Clinically Significant Changes in Clinical Laboratory Test Results
Clinically significant changes or abnormalities in hematology, chemistry, coagulation, and urinalysis results will be assessed.
Time frame: Through Week 16
Plan to share: No
No publications or documents are linked to this record.
Started Sep 2026 (actual). Primary completion is estimated for Dec 2027, 15 months after the start.
Of 31 phase 2 interventional studies under Chronic Urticaria, half reached primary completion within 19 months of starting (the median), counting those still running; a quarter within 16 and three quarters within 31. This study's planned 15 months is below that.
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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