Cyclopharm (ASX:CYC) shares are down by more than 40 per cent in early trading after the US Food and Drug Administration declined to immediately approve its nuclear lung imaging agent, Technegas.

The FDA issued what’s known as a complete response letter, raising questions about the characteristics, production and delivery of Technegas particles, which patients breathe in before a CT scan so doctors can better detect a pulmonary embolism — a life-threatening condition that occurs when a blood clot blocks an artery in the lungs.

Cyclopharm in January raised $30 million in a share placement to fund its expansion into the US market in advance of FDA approval, which the Sydney company expects will now be delayed by nine months.

“While the elements in the US FDA’s CRL (complete response letter) are attainable within the required timeframe, we are disappointed with this news of the additional technical information requests,” Cyclopharm managing director and chief executive James McBrayer said.

The company had been working closely with the FDA since lodging its new drug application for Techegas in March 2020, it said.

The FDA asked for information not raised by the 60 other jurisdictions, where Technegas has been used on over 4.4 million patients, Cyclopharm said.

Cyclopharm now expects FDA approval in the second half of 2022, rather than the second half of this year.

At 11.04am AEST, Cyclopharm shares were down 41.2 per cent to $1.61, their lowest level since September 2020.

With the plunge coming just before the end of the financial year, it may inspire some shareholders to sell for tax reasons.