Thioguanine for refractory psoriasis: A 4-year experience

Background: A variety of systemically administered drugs are used to treat psoriasis, including methotrexate, cyclosporine, acitretin, and hydroxyurea . Unfortunately some patients are unresponsive to these agents. For others, side effects and cumulative toxicity prevent continued use. Objective: Our purpose is to report the results of thioguanine (6-thioguani ne) treatment of 21 patients with refractory psoriasis. Methods: We conducted a retrospective review of the treatment courses of 21 patients with psoriasis who were treated with thioguanine. Daily dosing an d pulse dosing were both used, from 20 mg two times a week to 120 mg daily. All patients had been treated with other systemic therapies, and the major ity (86%) had been treated with methotrexate. Results: Patient outcome (response to treatment relative to baseline) was c lassified into 3 groups: those with more than 90% improvement, those with b etween 50% and 90% improvement, and those with less than 50% improvement. O utcome data were based on the patient's subjective rating of disease severi ty before the start of thioguanine therapy and during the entire treatment course. Of the 18 patients able to be evaluated, 14 of 18 (78%) had dramati c improvement (>90%); 3 of 18 (17%) had lesser improvement (50%-90%); and o nly 14 of 18 had less than 50% improvement. The mean duration of treatment was 15.5 months. The primary side effect was myelosuppression, mild in 9 of 18 (white blood cell counts ranging from 1600-3700/muL; platelet counts ra nging from 90,000-122,000/muL, and hematocrit values ranging from 24%-31%), and severe in 1 of 18 (white blood cell count of 1300/muL, platelet count of 17,000/muL, and hematocrit of 20%). Conclusion: Thioguanine appears to be an effective treatment for patients w ith severe recalcitrant psoriasis. Myelosuppression is a significant, but e asily monitored side effect that can now be more accurately predicted by de termining thiopurine methyltransferase levels before starting thioguanine. Further prospective studies are needed to establish criteria, which will ma ximize efficacy of this drug in the treatment of psoriasis and minimize tox icity.