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GPs advised to extend antibiotics in patients with emerging STI

Doctors should reduce the use of the single dose azithromycin 1g for Mycoplasma gentialium infection as it may be driving treatment failure and antibiotic resistance, according to a new review.

Single dose azithromycin 1g regimens in patients who tested positive for M. gentialium were associated with increased treatment failure rates and increased antibiotic resistance when compared with an extended regimen, taken as several doses over five days.

M. genitalium is an emerging STI that can cause non-gonococcal urethritis, cervicitis and pelvic inflammatory disease. A single dose of azithromycin 1g is currently one of the first-line treatment options for M. genitalium in the UK.

The review, led by researchers at the University of Bristol, looked at eight studies, including 435 M. genitalium-positive individuals who had received either azithromycin 1g as a single dose or as an extended regimen taken over five days.

When the results of the studies were pooled, there was a treatment failure rate of just under 14% in those who took the single dose, compared to just under 4% in those who took the extended regimen. All of the 4% who remained M. genitalium positive in the extended dose group had a mutation consistent with azithromycin resistance, as did 12% of the single dose group, corresponding to just under a 10% difference in resistance rate between the extended and single dose.

Consultant senior lecturer at University of Bristol Dr Paddy Horner, the lead author of the study, said: ‘A number of experts believe the rapid increase in drug-resistant M. genitalium is a consequence of the extensive use of azithromycin 1g for the treatment of STIs. This paper quantifies that risk for the first time, suggesting that one in eight (12 per cent) of individuals with M. genitalium will develop macrolide resistance when treated with azithromycin 1g.

‘It would therefore seem sensible to reduce the use of azithromycin 1g for treating STIs, unless M. genitalium can be excluded by nucleic acid testing, as used for chlamydia, before treatment.’

The authors suggest that single dose azithromycin 1g given is associated with higher treatment failure and resistance rates, but acknowledge that the evidence for the extended dose regimen being more effective is ‘moderate.’

They said in the paper: ‘Although fewer treatment failures were observed with the 5-day regimen… data from only three studies was available. When combining the data in a crude way, this equates to a difference in failure rate of 9.7% and a difference in resistance rate of 8.5%, which provides moderate evidence of a difference.’

Sex. Trans. Infect. 2017; available online 17th July

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