Concomitant administration of saxagliptin with the potent inhibitor of CYP3A4/5 ketoconazole, increased the Cmax and AUC of saxagliptin by 62% and 2.5‑fold, respectively, and the corresponding values for the active metabolite were decreased by 95% and 88%, respectively. Concomitant administration of saxagliptin with the potent CYP3A4/5 inducer rifampicin, reduced Cmax and AUC of saxagliptin by 53% and 76%, respectively. The exposure of the active metabolite and the plasma DPP4 activity inhibition over a dose interval were not influenced by rifampicin. The co‑administration of saxagliptin and CYP3A4/5 inducers, other than rifampicin have not been studied and may result in decreased plasma concentration of saxagliptin and increased concentration of its major metabolite. Glycaemic control should be carefully assessed when saxagliptin is used concomitantly with a potent CYP3A4 inducer.
Onglyza Summary of Product Characteristics, Bristol Myers Squibb – Astra Zeneca, December 2011.

Coadministration of ketoconazole (200 mg twice daily) and saxagliptin (20 mg or 100 mg single dose) increased saxagliptin AUC by ~2.5-3.7 fold and increased Cmax by ~1.6-2.4 fold. The AUC and Cmax of the active metabolite (5-hydroxy saxagliptin) decreased by 88% and 95% respectively when a single 100 mg dose of saxagliptin was coadministered with ketoconazole.  Similar significant increases in plasma concentrations of saxagliptin are anticipated with other strong CYP3A4/5 inhibitors (e.g., atazanavir, indinavir, nelfinavir, ritonavir, saquinavir). The dose of saxagliptin is 2.5 mg once daily when coadministered with strong cytochrome P450 3A4/5 (CYP3A4/5) inhibitors.
Onglyza US Prescribing Information, Bristol-Myers Squibb Co, December 2011.