AstraZeneca said today that the FDA has held off approval of its NDA for a fixed-dose combination of two marketed drugs—Onglyza (saxagliptin) and FARXIGA™ (dapagliflozin)—for adults with type 2 diabetes, with the agency instead requesting more clinical data.

The FDA’s request came in a Complete Response Letter (CRL), AstraZeneca said in a statement that announced the agency’s action without detailing what sort of additional data is being sought.

“The CRL states that more clinical data are required to support the application. This includes clinical trial data from ongoing or completed studies and may require information from new studies,” the pharma giant stated. “AstraZeneca will work closely with the FDA to determine the appropriate next steps for the NDA and remains committed to the development of the saxagliptin/dapagliflozin fixed-dose combination.”

The company added that the CRL is not expected to affect individual components of saxagliptin or dapagliflozin.

Last year, AstraZeneca reported positive results from a Phase III trial of the combination as a dual add-on therapy in adults with type 2 diabetes who were inadequately controlled on metformin. Patients treated with the combination achieved significantly greater reductions in HbA1c versus either agent alone plus metformin at 24 weeks, the company reported. The adjusted mean change from baseline HbA1c of -1.47% in the saxagliptin/dapagliflozin combination group compared to -0.88% in the saxagliptin group and -1.20% in the dapagliflozin group.

AstraZeneca also said at the time that more patients in the combination group (41%) achieved goal HbA1c levels of less than 7% compared to patients treated with saxagliptin alone (18%) and dapagliflozin alone (22%).

The FDA’s request for data delays the agency’s ultimate decision on the diabetes combination. “It’s not clear how long they will have to wait,” Sam Fazeli, an analyst with Bloomberg Intelligence, told Bloomberg News.

A best-case scenario for the length of the delay is eight to 10 months, but this could extend to a few years if new clinical trials are needed, according to Morgan Stanley analysts cited by Reuters.

Deutsche Bank analyst Richard Parkes told the wire service he foresaw a longer delay that probably reflected lack of data on the new formulation rather than safety or efficacy concerns—and that a product launch would be delayed by between 12 and 24 months.

Saxagliptin, first approved by the FDA in 2009, is a dipeptidyl peptidase-4 (DPP4) inhibitor, while dapagliflozin, approved by the agency last year, is a sodium-glucose cotransporter 2 (SGLT2) inhibitor. Both drugs are indicated as an adjunct to diet and exercise in adults with type 2 diabetes.

AstraZeneca collaborated with Bristol-Myers Squibb (BMS) in the development of both drugs and other diabetes treatments. In 2014, BMS completed the up-to-$4.3 billion sale of its global diabetes business to partner AstraZeneca.

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