Shares in NiCox have taken a battering this morning after staffers at the US Food and Drug Administration staff questioned the blood pressure benefits of the French group’s investigational pain drug naproxcinod.

The FDA has released documents ahead of a meeting of its Arthritis Advisory Committee and the Drug Safety and Risk Management Advisory Committee on May 12 to evaluate naproxcinod, the first in a new class of drugs known as CINODs (COX-inhibiting nitric oxide-donators). NiCox hopes the panelists will recommend the treatment for the relief of the signs and symptoms of osteoarthritis.

Naproxcinod is an improved version of naproxen, a non-steroidal anti-inflammatory drug that can increase blood pressure and cause stomach problems. NiCox believes that the data it has submitted shows that the drug can reduce these problems but some analysts fear that in terms of pain reduction, the levels are similar to naproxen.

Now, in the briefing documents, an FDA staffer is quoted as saying that naproxcinod’s effect on blood pressure is variable. The reviewer states that “typically, drugs with meaningful effects on cardiac outcomes” have an effect on blood pressure that “persists through the dosing interval. In this case, the potential impact on cardiac outcomes is unclear”. Staffers do believe, however, that the drug appears to be safe and effective.

NiCox remains confident and says naproxcinod is less likely to increase blood pressure than NSAIDs, which may be of particular importance to osteoarthritis patients with pre-existing hypertension, Analysts are concerned though and Sam Fazeli at Piper Jaffray issued a research note saying that “we believe the documents raise too many questions for the product to receive a favourable label," said Piper Jaffray analyst Sam Fazeli, who downgraded the stock to "underweight".

Investors are also worried and at 10.40am (UK time), NiCox shares were down 23.8% to 5.44 euros. The company has asked for trading in its stock to be suspended during the FDA panel meeting on Wednesday.