Cetirizine hydrochloride is a white, crystalline powder and is water soluble. Cetirizine hydrochloride syrup is a colorless to slightly yellow syrup containing Cetirizine hydrochloride at a concentration of 1 mg/mL (5 mg/5 mL) for oral administration. OTHER NON-ANTIHISTAMINES THAT MAY INTERFERE WITH SKIN TESTING (hold 1 day prior to appointment) Montelukast (Singulair) STEROIDS. Prednisone at 20 mg per day and methylprednisolone (Medrol) at 16 mg per day may interfere with skin testing.