Shares in AcelRx Pharmaceuticals (NSDQ:ACRX) fell more than -50% this morning after the company announced that it received a complete response letter from the FDA for its Dsuvia sufentanil sublingual tablet.

The FDA told the company that it can’t approve the new drug application in its present form, saying that AcelRx needs to collect additional data for at least 50 patients to assess the safety of the painkiller’s maximum dose described in its proposed labeling.

The regulatory watchdog added that AcelRx should make changes to the single-dose applicator’s directions to address use-related errors, including dropped tablets. These changes need to be validated through a human factors study, the FDA said.

“We believe the recommendations stated in the CRL are manageable and plan to fully cooperate with the FDA.  We remain focused on the NDA resubmission and our mission to provide physicians and patients with precise and efficient non-invasive pain management options for moderate-to-severe acute pain within medically supervised settings,” CEO Vincent Angotti said in prepared remarks.

ACRX shares were trading at $2.35 apiece in mid-morning activity today, down -56%.

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