A Phase 1 interventional study of REGN20423 and Placebo in Healthy Volunteer and Atopic Dermatitis, sponsored by Regeneron Pharmaceuticals. Recruiting at 9 sites in 2 countries. Open to participants aged 18 Years to 65 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-11-06.
Sponsored by Regeneron Pharmaceuticals · Phase 1, Interventional, and Treatment
This study will test an experimental study medicine called REGN20423 to see how effective it is in healthy participants (in Part A) and participants with atopic dermatitis (eczema) (in Part B). REGN20423 is a study medicine that is only used in clinical studies. REGN20423 has not previously been studied in humans.
The study is looking at:
1,591 studies on the registry are indexed under Dermatitis, Atopic; 286 are open to participants now.
This study's planned enrollment of 160 is above the median of 82 across 1,246 interventional studies indexed under Dermatitis, Atopic.
Browse Dermatitis, Atopic studies →Regeneron Pharmaceuticals is the lead sponsor of 411 studies on the registry; 90 are open to participants now.
Of its 125 completed or terminated interventional studies of FDA-regulated products, 79 (63%) have results posted.
Counted across the registry records on this site, refreshed daily.
The criteria were revised on the registry on Nov 6, 2026. See what changed
Part A: Enrolls healthy participants Part B: Enrolls participants with atopic dermatitis
Key Inclusion Criteria:
Part A:
Has a within 18 to 31 kg/m² (inclusive) at the screening visit
Part B:
Key Exclusion Criteria
Part A:
History of alcohol or drug abuse as determined by the investigator
Part B:
Note: Other protocol defined Inclusion/ Exclusion criteria apply
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.
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.
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.
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.
The other ingredients in a medicine besides the active drug, such as fillers, colours or preservatives.
Vaccines made with a weakened form of the germ, such as measles–mumps–rubella (MMR), chickenpox and yellow fever. They can be risky when the immune system is weakened. Flu injections are not live; the nasal flu spray is.
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.
Anti-inflammatory medicines such as prednisone, prednisolone and dexamethasone — not the anabolic steroids used for muscle.
Studies differ in what they allow: check which steroid medicines, routes (tablets, injections, creams, inhalers, eye drops) and doses this study accepts.
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.
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.
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.
Excipients
The other ingredients in a medicine besides the active drug, such as fillers, colours or preservatives.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Live vaccines
Vaccines made with a weakened form of the germ, such as measles–mumps–rubella (MMR), chickenpox and yellow fever. They can be risky when the immune system is weakened. Flu injections are not live; the nasal flu spray is.
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.
Corticosteroids (steroids)
Anti-inflammatory medicines such as prednisone, prednisolone and dexamethasone — not the anabolic steroids used for muscle.
Studies differ in what they allow: check which steroid medicines, routes (tablets, injections, creams, inhalers, eye drops) and doses this study accepts.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Drug: REGN20423 · Other: Placebo
Drug: REGN20423 · Other: Placebo
Administered per the protocol
Administered per the protocol
Occurrence of Treatment Emergent Adverse Events (TEAEs)
Time frame: Up to 69 weeks
Severity of TEAEs
Time frame: Up to 69 weeks
Concentrations of REGN20423 in serum
Time frame: Up to 57 weeks
Absolute values from baseline of total Interleukin 13 (IL-13)
Time frame: Up to 52 weeks
Absolute values from baseline of total Immunoglobulin E (IgE)
Time frame: Up to 52 weeks
Absolute values from baseline of total eosinophil counts in blood
Time frame: Up to 52 weeks
Absolute values from baseline of total periostin
Time frame: Up to 52 weeks
Absolute values from baseline of total Thymus and Activation-Regulated Chemokine (TARC)
Time frame: Up to 52 weeks
Percent change from baseline of total IL-13
Time frame: Up to 52 weeks
Percent change from baseline of total IgE
Time frame: Up to 52 weeks
Percent change from baseline of total eosinophil counts in blood
Time frame: Up to 52 weeks
Percent change from baseline of total periostin
Time frame: Up to 52 weeks
Percent change from baseline of total TARC
Time frame: Up to 52 weeks
Occurrence of Anti-Drug Antibodies (ADA) to REGN20423
Time frame: Up to 57 weeks
Magnitude of ADA to REGN20423
Time frame: Up to 57 weeks
Absolute change from baseline in Eczema Area and Severity Index (EASI) score
Part B EASI is a validated measure used to assess the severity and extent as a percentage by body area of head, trunk, arms and legs, and converted to a score of 0 to 6. Higher scores indicate higher improvement. Also, AD disease characteristics will be assessed for severity by the investigator or designee on a scale of "0" (absent) through "3" (severe)
Time frame: Up to 52 weeks
Percent change from baseline in EASI score
Part B
Time frame: Up to 52 weeks
Achievement of EASI-50
Part B
Time frame: Up to 52 weeks
Achievement of EASI-75
Part B
Time frame: Up to 52 weeks
Achievement of EASI-90
Part B
Time frame: Up to 52 weeks
Achievement of Investigator's Global Assessment (IGA) 0-1
Part B IGA is a frequently used clinician-reported instrument in clinical studies for rapid and easy assessment of disease severity of AD globally. It is based on a 5-point scale with range from "0" (clear) to "4" (severe), with higher scores indicating more severe disease
Time frame: Up to 52 weeks
Achievement of IGA 0-1 with reduction in IGA score by ≥2
Part B
Time frame: Up to 52 weeks
Achievement of a reduction in IGA score by ≥2
Part B
Time frame: Up to 52 weeks
Absolute change from baseline in % Body Surface Area (BSA)
Part B
Time frame: Up to 52 weeks
Absolute change from baseline in EASI
Part B
Time frame: Up to 52 weeks
Percent change from baseline in % BSA
Part B
Time frame: Up to 52 weeks
Percent change from baseline in EASI
Part B
Time frame: Up to 52 weeks
Plan to share: Yes — All Individual Patient Data (IPD) that underlie publicly available results will be considered for sharing
Supporting information: Study protocol, Statistical analysis plan, Informed consent form, Clinical study report, Analytic code
Time frame: When Regeneron has: received marketing authorization from major health authorities (e.g., FDA, European Medicines Agency (EMA), Pharmaceuticals and Medical Devices Agency (PMDA), etc.) for the product and indication or has globally discontinued development of the product for all indications on or after April 2020 and has no plans for future development made the study results publicly available (e.g., scientific publication, scientific conference, clinical trial registry) the legal authority to share the data, and ensured the ability to protect participant privacy
Access criteria: Qualified researchers can submit a proposal for access to individual patient or aggregate level data from a Regeneron-sponsored clinical trial through Vivli. Regeneron's Independent Research Request Evaluation Criteria can be found at: https://www.regeneron.com/sites/default/files/Regeneron-External-Data-Sharing-Policy-and-Independent-Research-Request-Evaluation-Criteria.pdf
Data sharing details ↗ · vivli.org
No publications or documents are linked to this record.
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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