The activities of drug inactive ingredients on biological targets

Inactive ingredients may not be inert Most drug formulations comprise mainly inactive ingredients known as excipients. Excipients are tested in animal studies and do not display toxicity at allowed concentrations, but their interaction with molecular targets has not been systematically explored. Pottel et al. examined excipient activity by combining large-scale computational screening with targeted experimental testing. They identified 38 excipients with activities against 44 targets. Several excipients were active in cell panels that predict tissue-level toxicity, and two are suggested to reach concentrations in vivo that overlap with their in vitro activities. Although most excipients are inert, some have activity that deserves further consideration. Science , this issue p. 403