The citrate salt form of ixazomib, an orally bioavailable second generation proteasome inhibitor (PI) with potential antineoplastic activity. Ixazomib inhibits the activity of the proteasome, blocking the targeted proteolysis normally performed by the proteasome, which results in an accumulation of unwanted or misfolded proteins; disruption of various cell signaling pathways may follow, resulting in the induction of apoptosis. Compared to first generation PIs, second generation PIs may have an improved pharmacokinetic profile with increased potency and less toxicity. Proteasomes are large protease complexes that degrade unneeded or damaged proteins that have been ubiquinated.