US regulators have issued a safety alert about Pfizer's antibiotic Zyvox after a recent trial found a higher chance of death in patients treated with the drug than other comparable antibiotics.

The US Food and Drug Administration published the alert after “new emerging safety concerns” about Zyvox (linezolid) emerged from a recent clinical study. The agency noted that this open-label, randomised trial compared the drug to vancomycin, oxacillin, or dicloxacillin in the treatment of seriously ill patients with intravascular catheter-related bloodstream infections.

The FDA said that in this study, patients treated with linezolid had a higher chance of death than did patients treated with any comparator antibiotic, and this was related to the type of organism causing the infection. Patients with Gram positive infections had no difference in mortality according to their antibiotic treatment but in contrast, Zyvox patients infected with gram-negative bacteria, both gram-positive and gram-negative bacteria, or who were infection-free when they entered the study saw a greater risk of death.

The FDA’s warning came as the UK’s Medicines and Healthcare products Regulatory Agency (MHRA) told Pfizer to suspend all advertising containing claims that Zyvox had superior cure rates compared with vancomycin after one such ad appeared in the British Medical Journal.

The MHRA said the move followed discussions with the company about concerns relating to the safety and efficacy of Zyvox compared with vancomycin in the aforementioned clinical trial involving patients with catheter-related infections.