Thank you for your inquiry.
In general, my experience with Plaquenil is similar to yours. There is, however, a sense that hydroxychloroquine is an effective agent in patients with urticarial vasculitis, especially associated with collagen vascular diseases, in particular systemic lupus erythematosus (1). Also it can be helpful in patients who have a primary leukocytic urticarial vasculitis. However, except for these particular instances, I know of no specific feature of urticaria which would make a patient particularly responsive to hydroxychloroquine. In most instances, we do not know why some patients respond to specific alternative therapies whereas others do not.
For your interest, there is an excellent review on alternative therapies for difficult to treat urticarial patients (2).
Thank you again for your inquiry and we hope this response is helpful to you.
1. Van der Horst JC and Bronsvel D. Urticarial vasculitis in a patient with systemic lupus erythematosus: A case report. Clinical and Experimental Dermatology, Volume 6 (5), 489-494, 1981.
2. Khan DA. Alternative agents in refractory chronic idiopathic urticaria: Evidence and considerations in their selection and use. J Allergy Clin Immunol: In Practice 2013; 1:433-440.
Phil Lieberman, M.D.