Eli Lilly has suffered a setback with the news that US regulators have delayed a decision on whether to approve a long-acting version of the blockbuster schizophrenia drug Zyprexa.

Lilly said that it has received a complete response letter from the US Food and Drug Administration (FDA) for Zyprexa (olanzapine) long-acting injection (LAI) for acute and maintenance treatment of schizophrenia in adults. The firm noted that the agency does not require any additional clinical trials for the continued review of the New Drug Application.

However the FDA has requested that Lilly is preparing a proposed risk evaluation and mitigation strategy, which will be submitted in the near future. Todd Durell, associate medical director for US neuroscience for Lilly, said that “we cannot speculate on the timing of a potential decision, but remain confident that, if approved, the long-acting depot formulation of olanzapine will offer an important option for treating this devastating and chronic illness".

In February, the FDA issued a not-approvable letter for the long-acting version of Zyprexa, saying it required additional information about the risk and cause of excessive sedation observed in some patients. In December, the new version received approval in Europe, where it is marketed as Zypadhera and analysts have predicted annual sales for the long-acting formulation of around $125 million by 2011, when the basic form comes off-patent.