US firm Nabi Biopharmaceuticals pulled the plug on two experimental polysaccharide vaccines against staphylococcal infections yesterday, sending its share price down the drain.

Nabi said its StaphVAX vaccine failed to achieve its primary objectives in a Phase III trial to treat Staphylococcus aureus-caused infections in patients with end-stage renal disease, and that all further studies would be halted until it had a thorough analysis of the data. It has also withdrawn a marketing application for the product in the European Union.

This is the second Phase III trial conducted by Nabi on StaphVAX. An earlier study showed that the drug was effective in reducing the incidence of S aureus infections compared to placebo.

The company said it would investigate the reasons behind the disappointing results, including an investigation of the vaccine itself to see if there are any differences between the batches used in the two studies, the quality of the antibody generated by the vaccine, and a look at whether S aureus itself has changed character in the years between the trials. These studies will take a few months to complete, it said.

Meanwhile, Nabi also said it would halt the development of Altastaph (S aureus immune globulin intravenous [Human]), designed for the prevention and treatment of S aureus infections, as it is based on the same capsular polysaccharide technology used in StaphVAX.

The news weighed heavily on Nabi’s share price, which buckled under the strain and fell more than 70% to close trading yesterday at $3.63.

Nabi insisted that its vaccine was highly immunogenic, but this did not provide comfort to some analysts. Banc of America Securities said in a research note that the failure of StaphVAX ‘calls into question Nabi's ability to develop vaccines’, as it downgraded Nabi to ‘neutral’ from ‘buy’.

Nabi’s CEO, Thomas McLain, said the company would now concentrate its efforts on two other programmes: NicVAX for smoking cessation in Phase IIb testing; and Civacir (hepatitis C immune globulin [Human]), an antibody to prevent hepatitis C virus infection in transplant patients, in Phase I/II. He stressed that Nabi still has $137 million dollars in liquid funds to support the ongoing development of its pipeline.

The company also has an ongoing revenue stream from PhosLo (calcium acetate), used to treat high blood phosphate levels in renal failure patients, which brought in $8 million in the third quarter, and Nabi-HB (hepatitis B immune globulin Human]), which added $10 million to Nabi’s total third quarter revenues of $31 million. It posted a net loss of $16 million in the period.

- Meanwhile. the news is also a blow to contract manufacturer Cambrex, which had been producing StaphVAX for Nabi. Cambrex said the termination of the programmes would not affect its 2005 financial guidance, but would not speculate on any impact next year.