The complete response letter (CRL) received by Assertio Therapeutics Inc.'s development partner, West Therapeutic Development LLC, regarding its NDA for cosyntropin (synthetic adrenocorticotropic hormone, ACTH) knocked Assertio's stock back 28% on Monday.

Lake Forest, Ill.-based Assertio noted that the FDA, in its CRL, stated "that certain pharmacodynamic parameters were not adequately achieved."

Neither had much to say about the FDA letter beyond Assertio President and CEO Arthur Higgins' comment that the two "will work together to determine how best to address the CRL."

Assertio (NASDAQ:ASRT) has struggled the past year as shares closed at $5.71 a year ago on Oct. 22 but closed Monday at 84 cents each, an 85% drop.

West wants to use the diagnostic drug to screen patients who may have adrenocortical insufficiency. Cosyntropin is an alcohol-free formulation of a synthetic analogue of ACTH, a hormone secreted from the pituitary gland that is responsible for the stimulation of the adrenal cortex. Cosyntropin is composed of the first 24 of 39 amino acids of natural ACTH and retains the full steroidogenic activity of natural ACTH.

Assertio has the exclusive rights to market cosyntropin in the U.S. and Canada. In February, the FDA acknowledged receiving the NDA for the injectable formulation of cosyntropin. At the time, Higgins said the acceptance brought a potential U.S. launch to early 2020. Cosyntropin then had an Oct. 19 PDUFA date.

A large stock slide happened on Aug. 9 as the price dropped from $2.81 to $1.52. On that day, the company announced it had entered separate, privately negotiated exchange agreements with a limited number of Assertio's outstanding 2.5% convertible notes due 2021. At the time, Higgins said the company had worked hard to pay down its senior secured debt and that the new transaction reduced the company's overall leverage and "represents further progress in our transformation to become a leading diversified biopharmaceutical business." The agreement called for exchanging about $200 million aggregate principal amount of exchanged notes for a combination of its new 5% convertible senior notes due Aug. 15, 2024, cash payment plus accrued but unpaid interest on the exchanged notes, and an agreed number of shares of Assertio's common stock. Assertio was to issue approximately $120 million aggregate principal amount of new convertible notes, pay an aggregate of approximately $30 million in cash and issue an aggregate of approximately 15.8 million shares of its common stock in the transactions. Assertio did not receive any cash proceeds from issuing the convertible notes or from shares of its common stock.

Assertio markets three products in the U.S. They are Gralise (gabapentin), a once-daily product to manage postherpetic neuralgia, that was launched in October 2011; Cambia (diclofenac potassium for oral solution), acquired by the company in December 2013, is a nonsteroidal anti-inflammatory drug for the acute treatment of migraine attacks; and Zipsor (diclofenac potassium liquid filled capsules), acquired by the company in June 2012, is a nonsteroidal anti-inflammatory drug to treat mild to moderate acute pain.

Assertio (pronounced as-sér-tee-o) was formerly known as Depomed Inc. As Depomed began to focus more on neurology, orphan and specialty medicines, the company brand shifted. The name change happened on Aug. 14, 2018, and the headquarters were relocated from Newark, Calif., to Illinois in search of pharmaceutical talent in Chicago's metro area.

Two weeks later, Purdue Pharma LP settled a patent infringement lawsuit from Assertio. Purdue was to pay Assertio $62 million in cash with $30 million in cash paid on Aug. 29, 2018, and another $32 million to be paid on Feb. 1, 2019. The agreement resolved all pending claims between the two companies. On Aug. 27, 2018, the stock sold for $6.38 per share.