• Male or female patients 15 to 75 years old (both inclusive).

• Diagnosis of CSU refractory to H1AH, as defined by all of the following:

‣ Diagnosis of CSU at the time of screening, urticaria history ≥ 6 months at the time of randomization

⁃ The presence of itch and hives for ≥ 6 consecutive weeks within half year prior to randomization despite use of H1AH treatment during this time period;

⁃ UAS7 score (range 0-42) ≥ 16 and itch component of UAS7 (range 0-21) ≥ 8 during 7 days prior to randomization (Day 1);

⁃ In-clinic UAS ≥ 4 on at least one of the screening visit days;

⁃ Patients must have been on an approved dose of an H1AH for CSU for at least the 3 consecutive days immediately prior to the screening visit and must have documented current use on the day of the initial screening visit.

• Voluntarily sign the informed consent form. Willing and able to complete a daily symptom diary for the duration of the study, and comply with the protocol requirements.

• Patients must not have had any missing diary entries in the 7 days prior to randomization.

• Women of childbearing age have negative pregnancy tests and are not in the lactation period at the time of screening. Both male and female patients must agree to practice contraception from the signing of informed consent to 6 months after the last dose of study drugs.