I have heard that trimethoprim / sulfamethoxazole (Septra, Bactrim) causes QT prolongation so is not a good alternative to fluoroquinolones in at-risk patients. Is this true?
Many who are worried about QT prolongation and Torsades des Pointes steer clear of cipro. A natural alternative antibiotic option tends to be septra, however the word on the street is that septra is also QT prolonging. I have investigated this issue thoroughly and wanted to share my bottom line.
In the Septra monograph it is written that Septra prolongs the QT with a stated incidence of <1%. As you are aware, the way that monographs are written is not conducive to reliably identify adverse effects. If ANY side effect was observed in a clinical trial, regardless of how it compared to the placebo arm, the manufacturer lists it in the monograph. Statistical comparisons are not performed, and clinical implications of abnormalities of surrogate markers and not interpreted, especially for older drugs. All we know from the monograph that a very small proportion of people on Septra experienced an increased in their QT. How this was found, the magnitude of the increase, how many people it affected or if this differed from placebo is not stated. We also know for a fact that the QT is highly sensitive and varies throughout the day, and it is unlikely if the manufacturer took this into consideration. All it could have been is an incidental finding in one or two people, unrelated to septra and not clinically significant. Torsades de Pointes has NEVER been observed with Septra and is not listed in the monograph. I have searched extensively for any case report or clinical evidence that Septra prolongs the QT and could not find ANY. If I search QT prolongation and fluoroquinolones many publications emerge. There is also NO study, not even a case report that links Septra with TdP. In fact, in one study of HIV patients treated with pentamidine or Septra, it was shown that Septra did not prolong the QT (and neither did pentamidine). Septra can be linked to dysrhythmias because it can cause hyperkalemia, but this is different. If you ever have anyone ask you if Septra prolongs the QT or is linked to TpD, please tell them there is no evidence that supports this.