The objective of this study was to evaluate the efficacy and safety of cetirizine hydrochloride injection in the treatment of acute urticaria.The participants were randomized to receive cetirizine hydrochloride or diphenhydramine hydrochloride.

Inclusion Criteria:

1. Age range: 18 - 65 years old (inclusive of the threshold value), gender not limited;
2. Diagnosed with acute urticaria (the definition of acute urticaria: spontaneous wheals and/or angioedema attacks ≤ 6 weeks);
3. At screening，the severity score of pruritus of the patient was ≥ 1 point ;
4. At screening，the degree score of wheals/erythema of the patient assessed by the investigator was ≥ 1 point ;
5. Be willing and able to give informed consent.

Exclusion Criteria:

1. Patients in whom an antihistamine are contraindicated (such as those with angle-closure glaucoma, symptomatic benign prostatic hyperplasia, etc.);
2. Patients who used H1 antagonists (such as diphenhydramine, cetirizine, loratadine, fexofenadine, levocetirizine, desloratadine, etc.) within 2 hours before randomization;
3. Patients who used H2 antagonists (such as cimetidine, ranitidine, famotidine, roxatidine, etc.) within 2 hours before randomization;
4. Patients who used doxepin within 2 hours before randomization;
5. Patients who received steroid hormone treatment for acute allergic reactions within 4 hours before randomization;
6. Patients who used epinephrine within 20 minutes before randomization;
7. Patients who are known to be allergic to hydroxyzine, cetirizine, levocetirizine, diphenhydramine;
8. Pregnant or lactating women; or those who have a pregnancy plan or plan to donate sperm/eggs from the screening day to the end of medication within 1 month; or those who are unwilling to take one or more contraceptive measures from the screening day to the end of medication within 1 month;
9. Patients with urticarial drug eruption;
10. Patients with acute urticaria who have concurrent symptoms such as laryngeal edema, allergic asthma, anaphylactic shock during screening;
11. Patients with urticarial vasculitis, hereditary angioedema, antihistamine-resistant urticaria or skin diseases that interfere with the evaluation of treatment efficacy during screening;
12. Patients with a history of immunodeficiency;
13. Patients with other major medical conditions (such as blood diseases, cardiovascular and cerebrovascular diseases, liver diseases, kidney diseases, etc.) or mental disorders and judged by the investigator to be unsuitable to participate in this study;
14. Patients who are concurrently using P-glycoprotein inhibitors (such as cyclosporine, itraconazole, dronedarone, amiodarone, quinidine, verapamil, etc.) during screening;
15. Patients who participated in other clinical trials within 3 months before screening (excluding those who only participated in the screening of the clinical trial but did not use the trial drugs or devices);
16. Patients with acute urticaria accompanied by fever during screening;
17. Patients engaged in dangerous jobs such as driving, high-altitude work, mechanical operation, etc., and cannot stop within 48 hours after medication;
18. Other various situations.