Shares in Basilea have collapsed this morning on the news that US regulators have delayed a decision on the firm’s superbug antibiotic ceftobiprole, which is partnered with Johnson & Johnson.

The US Food and Drug Administration has issued J&J with a complete response letter for ceftobiprole which has been filed for the treatment of complicated skin and skin structure infections including diabetic foot infections. In the letter, the agency says that an inspection has revealed that there was “a failure to ensure proper monitoring of the studies” filed to accompany the New Drug Application.

The FDA has requested information on J&J's clinical quality assurance programmes and asked for a new audit plan that also addresses “deficiencies in contract research organisation monitoring” As a result of this problem, the agency says it is unable to review the clinical data included in the submission “until issues of data integrity have been resolved”. J&J has to fully respond to this action letter within one year.

The effect on Basilea shares has been considerable and at 10.30 this morning, UK time, the stock was down almost 29% to 108.40 Swiss francs. The firm’s chief executive Anthony Man said “we are deeply disappointed with the further delay in the review of the US NDA application”.

He claimed that ceftobiprole addresses “the very serious medical need related to resistant bacterial infections including MRSA”, noting that the drug has been approved or recommended for approval in a number of countries including the European Union “based on two large independent and well designed trials”. He added that Basilea will be working with J&J and the FDA to address the outstanding issues as soon as possible, saying “these events have not altered in any way our confidence in the efficacy and safety profile of ceftobiprole".

Ceftobiprole is approved in Canada and Switzerland, where it will be marketed as Zevtera, and has been recommended for approval in the EU. However, US regulators have proved to be much tougher to convince and the FDA had already issued an approvable letter for the antibiotic in March, indicating that further assessment of clinical data was needed.