SOURCE: Maley A, Swerlick RA. Azathioprine treatment of intractable pruritus: A retrospective review. J Am Acad Dermatol 2015;73:439-443.
When we can identify and remove the source of pruritus, we would like to do so. Unfortunately, sometimes the cause cannot be identified, as in recurrent urticaria, for which an inciting agent remains unconfirmed as often as half of the time. Additionally, there are times when a necessary or preferred treatment must be continued despite pruritus, as is sometimes the case with opioid analgesics. While traditional antihistamines often effectively relieve pruritus, the tricyclic antidepressant doxepin is actually many times more potent than other antihistamines and also effectively treats pruritus. However, since it is highly sedating at doses effective for pruritus, it generally is not used as a first line-treatment. Although systemic steroids are often effective, their side effect profile limits chronic use.
Based on the theory that pruritus may be an immunologically mediated phenomenon — corroborated by the frequency of pruritus relief through systemic steroid administration — Maley and Swerlick administered azathioprine to patients (n = 96) with intractable pruritus. Azathioprine inhibits T-cell and B-cell proliferation, leading to its role in prevention of organ transplantation rejection. Each of these patients had suffered long-term pruritus (mean = 53 months), and the mean pruritus score was 9.25 on a 10 point scale. Azathioprine was found to be highly effective: The post-treatment pruritus score came down from 9.25/10 to 1.63/10. Advantages of azathioprine include that it is once daily, inexpensive, and drug levels can be monitored. Disadvantages include consequences of immune suppression, including malignancy. While probably not a treatment to be commonly employed in the primary care setting, this retrospective study supports consideration of azathioprine when other efficacious treatments have been exhausted.