Evaluation of Utility of Pharmacokinetic Studies in Phase I Trials of Two Oncology Drugs

Purpose: There are many phase I trials of oncology drug combinations, very few of which report clinically significant pharmacokinetic interactions. We hypothesized that the utility of such pharmacokinetic drug–drug interaction (DDI) studies is low in the absence of a mechanistic hypothesis. Experimental Design: We retrospectively reviewed 152 phase I (two drug) combination studies published between 2007 and 2011. Results: Only 28 (18%) studies had an implicit or explicit rationale, either inhibition/induction of a drug-metabolizing enzyme or transporter, cosubstrates for the same enzyme or transporter, potential for end-organ toxicity, or protein binding. Only 12 (8%) studies demonstrated a statistically significant DDI, on the basis of change in clearance (or area under the curve) of parent drug and/or active metabolite. There was a strong association between a rationale and a demonstrable drug interaction, as only 2% of studies without a rationale demonstrated a DDI, compared with 32% of studies with a rationale (Fisher exact test; P < 10−6). Conclusion: DDI studies should not be routinely performed as part of phase I trials of oncology combinations. Clin Cancer Res; 19(21); 6039–43. ©2013 AACR.