Around 20 per cent of those taking the antibiotic ciprofloxacin to prevent anthrax infection will experience adverse reactions to the drug, say the US Centers for Disease Control and Prevention (CDC).

These data come from an analysis of adverse events seen in 1132 individuals in Boca Raton, Florida, who received antimicrobial prophylaxis after their presumed exposure to Bacillus anthracis following the first case of inhalation anthrax reported there. Of these, 970 were given ciprofloxacin.

To assess the adverse effects, those still taking the antibiotics on or around day 7 or day 14 (80 per cent) filled in a questionnaire. The responses indicated that 95 (19 per cent) of 490 respondents had experienced one or more adverse reactions in the form of itching, breathing problems, or swelling of the face, neck or throat.

Further communications and a review of the medical records indicated that six patients had sought medical attention and had discontinued taking their original medication, possibly due to the adverse side-effects.

As widespread use of ciprofloxacin and other anti-anthrax antibiotics has been rare until only recently, the side-effects are not well documented. Now, with an estimated 32,000 people taking these drugs preventatively (and about 5000 advised to take a 60-day course), their adverse effects are becoming more evident (MMWR, 2001; 50: 973-6).