Patients who are receiving concomitant medications should not systematically be excluded from phase I studies.

This retrospective study was designed to evaluate possible relationships between the number and types of concomitant medications administered to patients on the first day of therapy in phase I trials and demographic characteristics, outcome measures and toxicities. Concomitant medications received by 690 patients enrolled on 28 phase I trials between August 1985 and January 1996 were grouped into 31 categories based on the American Hospital Formulary Service 1993. These patients received 1650 cycles of treatment with investigational agents (median 2 cycles per patient). Median duration on-study was 49 days (range 1-776 days). Clinical response rate (complete, partial, minor) was 3.8%. Only three toxic deaths occurred (0.4%). Nearly all patients (90.9%) received at least one concomitant medication on the first day of therapy. The number of concomitant medications directly correlated with poor performance status (rSp = 0.27, p < 0.0001) and indirectly with duration on-study (rSp = -0.18, p < 0.0001). The dose of the investigational agent administered during the first course of therapy was not related to concomitant medications on the first day of therapy. Most importantly, no relationships were observed between concomitant medications and either toxicities or clinical response to therapy. We conclude that patients who are receiving concomitant medications should not systematically be excluded from phase I studies.