Magazine article Drug Topics

Assessing Risk to QT Interval

Magazine article Drug Topics

Assessing Risk to QT Interval

Article excerpt

A 70-year-old woman, T.R., has been transferred from an extended care nursing facility to your hospital with symptoms of fever, dyspnea with respiratory difficulty, cough, and sputum production. Her current medications include methadone 200 mg/ day (pain syndrome), risperidone (Risperdal, fanssen) 2 mg twice daily, digoxin 0.125 mg daily, and furosemide 20 mg twice daily. T.R.'s chest X-ray shows a pulmonary infiltrate in the right middle and upper lobes of the right lung with lobar consolidation. She is diagnosed with pneumonia, and her physician prescribes moxifloxacin (Avclox, Bayer) 400 mg IV/24 hours. Your student calls this order to your attention; her journal club recently discussed the problem of QT prolongation and this regimen concerns her. What do you recommend?

The medications T.R. is already taking may indicate a significant underlying dysrhythmia. She is receiving a high dose of methadone, which according to the literature, can contribute to QT prolongation and torsades de pointes. She is taking digoxin and furosemide without potassium supplementation (T.R. could be hypokalemic), and she is elderly. Studies show individuals with underlying cardiac anomalies, advanced age, female sex, concurrent QT-prolonging agents, hypokalemia, or hypomagnesemia have an increased incidence of QT prolongation and torsades de pointes. These factors should be considered in antibiotic choice.

According to recent pneumonia guidelines, individuals presenting from long-term care facilities with pneumonia should receive a respiratory fluoroquinolone (levofloxacin, moxifloxacin) as inpatients. The QT prolongation potential associated with fluoroquinolones differs among individual agents: Sparfloxacin (Zagam, Mylan) and grepafloxacin (Raxar, Otsuka) show the greatest incidence; other agents, e.g., moxifloxacin and levofloxacin (Levoquin, Ortho-McNeil), show lesser incidence. These conclusions are drawn from multiple trials of more than 200 patients and adverse reporting through the FDA. We do not know how well T.R. is rate/rhythm controlled, so to err on the side of caution, it is best to proceed with the secondary guideline recommendation, a beta-lactam and an advanced macrolide.

My recommendation would be amoxicillin/clavulanate extended-release 2,000 mg every 12 hours (renally adjusted) and azithromycin 500 mg IV for two days, followed by 500 mg orally for seven days. This was based on the possibility that moxifloxacin and methadone may additively contribute to QT prolongation and possible torsades, as well as the patient's other risk factors for QT prolongation. …

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