Ipsen has placed a partial clinical hold on all global sites of the Phase II PVO-1A-202/204, PVO-2A-201, and Phase III PVO-1A-301 clinical trials assessing palovarotene.

The clinical hold is for paediatric patients aged below 14 years and comes after discussions with the US Food and Drug Administration (FDA).

Palovarotene is an investigational retinoic acid receptor gamma (RARγ) agonist. Ipsen added the drug to its portfolio with the acquisition of Clementia Pharmaceuticals.

In these Phase II and Phase III trials, the drug is being assessed for the chronic treatment of fibrodysplasia ossificans progressiva (FOP) and multiple osteochondromas (MO).

The clinical hold was placed after safety reports revealed early growth plate closure in paediatric FOP patients treated with the drug. Ipsen recently submitted the reports to the FDA.

This hold is contingent on a pending review of further information about the serious adverse events. The US regulator intends to request additional details within the coming 30 days.

While no such events were observed in the MO data reported to date, the study has also been put on hold because the events were associated with chronic dosing in the FOP programme.

The MO study mainly consists of paediatric patients, leading to a temporary halt of treatment for all participants, along with further enrolment.

The company said in a statement: “Ipsen is committed to researching and developing therapies for children and adults living with FOP and MO, two rare and devastating bone diseases with no current therapeutic treatment options.

“Ipsen is committed to working diligently with the FDA to provide all requested information with the goal of resolving the partial clinical hold.”

The company is currently working to submit a new drug application (NDA) to the FDA for palovarotene in acute/flare-up FOP.