Non-clinical combination toxicology studies: strategy, examples and future perspective

Over the last decade, combination of drugs in all stages of pharmaceutical development has accelerated availability of promising new therapies for difficult to treat diseases. Safety assessment of combined drugs to be tested in humans can occur at a critical path prior to proceeding in clinical testing. A recent survey by The International Consortium for Innovation and Quality in Pharmaceutical Development (IQ DruSafe) summarized member companies' approaches to combination safety strategies. In addition, feedback from Health Authorities (HAs) support a case-by-case scientific approach in assessing combination products' safety in accordance with the International Council on Harmonization (ICH) guidelines. Here, we present Pfizer's drug combination safety approach for various therapeutic areas (TA) including inflammation and immunology, metabolic, and anti-cancer products. There is no one-size-fits-all approach; rather, our main considerations include: strength of the existing clinical safety data for the individual compounds, common target organs, the potential for a synergistic effect, potential drug-drug interaction, routes of administration of each product and disease indications. No formal toxicity studies are considered necessary for anti-cancer drugs, while safety endpoints may be collected in preclinical pharmacology studies especially when the combined drugs present a novel mechanism. Combination safety studies when conducted for non-cancer indications can range from 2 to 13-weeks in duration, conducted usually in rodents, with dosages of individual molecules within clinical pharmacologic ranges. A case-by-case strategy guided by scientific rationale and in close collaboration with HAs remains the best approach to decide on the design and conduct of combination safety studies.