Secondary treatment of polycythemia rubra vera with 6-thioguanine

6-thioguanine, an antimetabolite not potentiated by allopurinol, has been used in the treatment of 29 patients with polycythemia vera. All but two of the patients had been treated previously by venesection and/or radioactive phosphorus (32p) and/or alkylating agents. The usual dose was 40-160 mg daily alternate weeks according to individual response. The treatment period varied from 6-66 months (mean, 31 months). Of 27 evaluable patients 24 (89%) responded to treatment and at one year there was a significant fall in all blood count parameters. Seven patients relapsed while on treatment and four were withdrawn because of side effects. 6-thioguanine merits further evaluation in the management of polycythemia vera, particularly in those patients who have received large cumulative doses of 32p and/or alkylating agents and in whom an alternative mode of therapy is desirable.