Friday, May 3, 2013

Azithromycin & Cardiovascular Risk, Belabored


Last year, I noted a study concerning a report of excess deaths associated with azithromycin use.  This study, a retrospective, observational cohort from Tennessee Medicaid data suggested a death rate double that of other antibiotics.  This led to the FDA issuing a warning regarding azithromycin use.

I thought all this fuss was absurd – the data quality was one step above junk and the absolute magnitude of the proposed harms was trivial.

Now, we have the counterpoint – a retrospective, observational cohort from Denmark, using their national health system database to compare prescriptions for azithromycin to penicillin V over the last 13 years.  In their cohort, there's an obvious increase in risk of death from cardiovascular causes simply from being prescribed any antibiotics – but no difference between azithromycin and penicillin V.  This seems to indicate either the systemic infectious process contributes to excess cardiovascular risk, or that respiratory symptoms are being misdiagnosed as infectious rather than cardiovascular.  The absolute effect in their propensity matched cohorts is also tiny – a handful of patients or fewer spread across a million prescription events.

The accompanying opinion seems to attempt to justify the FDA review based on the wide confidence intervals in the Danish study – the OR for death from cardiovascular causes vs. penicillin V is 1.06 (0.54 – 2.10) and doesn't statistically contradict the Tennessee study.  However, yet again, I would point to the reason behind the wide confidence intervals – the nearly trivial absolute magnitude of the harms, which amount to fractions of a patient per 1000 patient-years.

Again, plenty of reasons to responsibly reduce azithromycin prescriptions – but this cardiovascular hullabaloo probably isn't one of them.

"Use of Azithromycin and Death from Cardiovascular Causes"
http://www.nejm.org/doi/full/10.1056/NEJMoa1300799

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