The purpose of this study is to assess the clinical activity on refractory moderate-to-severe pruritus of a single intravenous (IV) dose of REGN846 in adult patients with moderate-to-severe atopic dermatitis (AD).

Inclusion Criteria:

Inclusion criteria include, but are not limited to the following:

1. Men and women between the ages of 18 and 65; women must be postmenopausal or surgically sterile
2. Patients must have applied a stable dose of an additive-free, basic, bland emollient twice daily for at least 7 days before the baseline visit
3. Chronic Atopic Dermatitis (AD)
4. Body mass index (BMI) between 18.0 and 30.0 kg/m2, inclusive.
5. Refractory pruritus for ≥ 6 weeks before screening. Pruritus should be associated only with AD and not with any other condition(s).
6. Itching associated with AD

Exclusion Criteria:

Exclusion criteria include, but are not limited to the following:

1. A history of listeriosis.

2. Presence of any 1 of the following tuberculosis (TB) criteria:

   1. A history of active TB
   2. A positive QuantiFERON TB test at the screening visit
   3. Chest radiograph (posterior-anterior and lateral views) at screening or within 3 months before the screening visit (radiology report must be available) with results consistent with prior TB infection (including but not limited to apical scarring, apical fibrosis, or multiple calcified granuloma). This does not include non-caseating granulomata.

3. Persistent chronic or active recurring infection requiring treatment with antibiotics, antivirals, or antifungals within 4 weeks prior to the screening visit.

4. Any clinically significant physical abnormalities observed during the screening visit.

5. Diabetic, hypertensive, or any known atherosclerotic vascular disease.

6. Hospitalization for any reason within 60 days of the screening visit.

7. History of or positive human immunodeficiency virus (HIV) screen result at the screening visit.

8. History of positive blood test for hepatitis B/hepatitis C or positive hepatitis screen result at the screening visit.

9. Known sensitivity to doxycycline or tetracycline.

10. Known sensitivity to any of the components or excipients of the investigational product formulation or history of hypersensitivity to any biologic agent.

11. Participation in any clinical research study evaluating another investigational drug or therapy within 30 days or at least 5 half-lives (whichever is longer), of the investigational drug prior to the screening visit.

12. Any medical or psychiatric condition that in the opinion of the investigator or Regeneron, would place the patient at risk, interfere with participation in the study or interfere with the interpretation of study results.