To obtain the pharmacokinetics of cetirizine in Chinese children with allergic disease.

Inclusion Criteria:

1. The informed consent form was voluntarily signed by the legal guardians of the subjects (children aged ≥8 years should participate in the informed consent process and sign the informed consent form).
2. Pediatric patients, whether they are outpatients or inpatients, who require oral cetirizine therapy.
3. The children was clinically diagnosed with allergic diseases such as eczema, urticaria, asthma, and allergic rhinitis.
4. Pediatric patients had not taken other antiallergic drugs 72 hours before screening.

Exclusion Criteria:

1. Abnormal liver function (ALT or AST > 2 times the upper limit of normal).
2. Abnormal renal function (serum creatinine above the upper limit of normal or GFR < 10 mL/min)
3. Electrolyte abnormalities (potassium or magnesium < 0.8 times lower limit of normal, > 1.2 times upper limit of normal)
4. Children who were allergic to cetirizine or had a history of serious adverse reactions.
5. Pediatric patients with unstable vital signs.