By Jonathan Amos BBC News Online science staff in Leicester

The gross misuse of the antibiotic Cipro following last year's anthrax attacks in the United States could have serious consequences in the war against resistant bacteria, says an expert on the drug.

In the weeks following the discovery of contaminated letters in the American postal system, about 30,000 official prescriptions for Cipro were handed out, but thousands more panic-struck people obtained it over the net or over the border in Mexico.

Dr Chris Willmott, from Leicester University, UK, who has studied how the drug works, believes the widespread abuse could result in many more patients in US hospitals experiencing antibiotic-resistant complications in future.

"The more you use an antibiotic, the more bacteria become exposed to it and the more likely it is that resistance will develop."

Real risk

Cipro (ciprofloxacin) is what is known as a fluoroquinolone antibiotic. It is a man-made drug that acts against a wide range of pathogens and has, as a consequence, become a major weapon in the fight against infection.

Because of its importance, Dr Willmott questions whether it should have been recommended for use as a preventative measure, especially when less important classes of drugs could have done the job equally well.

"Resistance may not only develop in Bacillus anthracis, the causative agent of anthrax, which is not in fact passed from person to person and is thus not contagious, but also in other bacteria such as Staphylococcus aureus and Streptococcus pneumoniae.

"This was a massive use of a drug and there is a very real risk that more people will develop drug-resistant complications, which lead on to death, than died in the initial anthrax attacks.

Right decision

Ultimately, there were 22 confirmed cases of the disease in its different manifestations, including five deaths resulting from the respiratory form of anthrax.

Dr Willmott said a mathematical model in the US had suggested that 5,000 legal prescriptions given to potentially exposed workers in Florida, New Jersey and Washington had probably caught just nine cases of the disease.

"Set this against the situation where about two people an hour in American hospitals are dying because of complications related to drug-resistant bacteria - that's 17,000 people a year. In which case, you do wonder whether this was an appropriate use of ciprofloxacin."

It was totally right, Dr Willmott said, that the Centers for Disease Control and Prevention in the US eventually switched their recommendation for precautionary treatment of anthrax from Cipro to a less important antibiotic, Doxycycline.

Dr Willmott made his comments at the British Association's science festival in Leicester.