What is it?
Hydroxychloroquine is an antiinflammatory drug and antimalarial agent. The relative safety of the low doses, and the low cost of hydroxychloroquine makes it a reasonable agent in the treatment of refractory chronic urticaria (CU). One of the disadvantages is the relatively slow onset of action.
How does it work?
The mechanism of action includes suppression of T lymphocyte activation and antigen processing.
Paucity of research data
Apparently, there is only one published study in PubMed, from 10 years ago, which included only 18 patients with chronic urticaria (http://www.ncbi.nlm.nih.gov/pubmed/15086698). The patients were treated with a combination of therapies for CU (H1 antihistamines, H2 antihistamines, glucocorticoids, and doxepin) and randomized to receive either:
- hydroxychloroquine (5 mg/kg daily)
- or no additional drug
After 3 months of treatment, patients in the hydroxychloroquine arm had improved quality of life. Hydroxychloroquine was well tolerated for 12 weeks (200 mg of hydroxychloroquine twice daily). However, because of small size and 3 dropouts (from 21 to 18), the study was underpowered to detect significant differences.
The 2014 edition of UpToDate includes the expert recommendation to start hydroxychloroquine with a dose of 200 mg twice a day. A 3-month trial is usually required to determine effectiveness. Hydroxychloroquine rarely causes serious side effects. The most common adverse reactions are related to the gastrointestinal tract (nausea), skin (various macular lesions), and central nervous system (headache).
Ophthalmologic problems, including corneal deposits (reversible) and retinopathy (potentially vision threatening) are possible, but rare with the low daily doses of hydroxychloroquine used in CU.
No studies have evaluated the ideal length of treatment.
The risk of retinopathy is low in the first 5 years of use, but after 5 years of use it increases to approximately 1%.
Recent recommendations from the American Academy of Ophthalmology (http://www.ncbi.nlm.nih.gov/pubmed/21292109) are:
- baseline ophthalmologic examination within the first year of starting hydroxychloroquine
- annual examinations after 5 years of therapy
Chronic Urticaria Treatment Options in 6 Steps (click to enlarge the image).
Impact of hydroxychloroquine therapy on chronic urticaria: chronic autoimmune urticaria study and evaluation. Intern Med J. 2004 Apr;34(4):182-6.
PubMed search for "hydroxychloroquine chronic urticaria" shows the lack of research on the topic, most results are from review articles http://buff.ly/1zEUBxo
Chronic urticaria: Treatment of refractory symptoms. UpToDate, 2014.
Alternative agents in refractory chronic urticaria: evidence and considerations on their selection and use. J Allergy Clin Immunol Pract. 2013 Sep-Oct;1(5):433-440.e1. doi: 10.1016/j.jaip.2013.06.003. Epub 2013 Aug 2.
Image source: Urticaria, Wikipedia, public domain.