09:17 AM

415 - Antivirals for Influenza, Electronic Interference with Cardiac Devices

Take 3 – Practical Practice Pointers©

From the Literature

1) A Comparison of Antivirals for Influenza

As we start flu season in the midst of another COVID-19 surge, it’s time review our influenza antiviral choices. To compare the available antivirals on the market, a research team has published a new systematic review with network meta-analysis, which estimates the comparative effectiveness of several drugs using placebo-controlled trials. Data about four drugs [oseltamivir (oral), baloxavir (oral), zanamivir (inhaled), and peramivir (intravenous)] were pulled from 26 trials (almost 11,900 participants). The search for trials did not include unpublished studies beyond clinicaltrials.gov but was otherwise acceptable. The overall risk of bias was moderate for the trials – mostly due to issues of blinding and outcome assessment. The authors employed several techniques (sensitivity analyses, etc.) to ensure their analysis was conservative. The authors focused on the outcomes of TTAS (time to alleviation of symptoms) and influenza complications for the meta-analysis and looked at total adverse events, nausea, and vomiting as safety concerns.

The results are available only as relative changes in the outcomes compared to placebo and each other, so they are only summarized below.

Overall, for the oral/inhaled agents (easiest to implement in outpatient care):

  • Zanamivir (Relenza) was found to have the lowest TTAS (2/3 of that of placebo) of all the choices, but this was limited by a relatively high rate of adverse events and nausea.
    • It should be noted that zanamivir use can lead to bronchospasm, and so should be used with caution in asthma or COPD.
  • Oseltamavir (Tamiflu) was moderately effective (better against complications than at reducing TTAS) and had a low-moderate side effect profile.
  • Baloxavir (Xofluza, the newest agent available) does well to prevent complications of influenza but has only a small effect on TTAS and has a moderate rate of nausea and vomiting. Baloxavir is a single-dose treatment.

The authors did find evidence of publication bias in this review, a common problem in reviews of influenza therapies.

John’s Comments:

This reasonably well-done systematic review only tells us which of the available agents works better than the other. What they don’t tell us is how much benefit each medication provides for our patients. The best estimates of the effect of oseltamivir find that it reduces influenza TTAS by almost a single day. Zanamavir improves this by about 10%. Baloxavir seems to reduce influenza complications by about 30% over other agents and 60% over zanamivir, but a baseline rate of complication reduction by these agents is difficult to pin down between studies. The 2014 Cochrane review (Link) of oseltamivir and zanamivir characterizes these as small. All in all, there seems to be a limited magnitude of benefit for these agents. Consider them for patients who are at higher risk for complications from influenza, and make sure patients are aware of their side effects.


  • Liu J-W, Lin S-H, Wang L-C, Chiu H-Y, Lee J-A. Comparison of Antiviral Agents for Seasonal Influenza Outcomes in Healthy Adults and Children: A Systematic Review and Network Meta-analysis. JAMA Network Open. 2021 Aug 13;4(8):e2119151–e2119151. Link


From the FDA and the Literature

2) Smartphone Interference with Cardiac Devices

Many implanted medical devices are designed with a “magnet mode” to allow for safe operation during certain medical procedures such as undergoing an MRI scan. These safety features are typically engaged by physicians with the use of a high field strength magnet that is placed near the implanted device placing it into a “magnet mode.” Removal of the magnetic field causes the device to return to normal operation.

Some consumer electronic devices, such as certain cell phones and smart watches, include high field strength magnets. Recent studies have shown that consumer electronic devices with high field strength magnets may cause certain implanted medical devices to switch to “magnet mode” and suspend normal operations until the magnet is moved away from the medical device.

Because of this possibility, the FDA published a recommendation in May that consumer electronic devices that may create magnetic interference, including cell phones and smart watches, should be kept at least six inches away from implanted medical devices, in particular cardiac defibrillators.

People with implanted medical devices are advised to take some additional simple precautions, including:

  • Not carrying consumer electronics in a pocket over the medical device. 
  • Checking the device using a home monitoring system, if they have one.
  • Talking to their health care clinician if they are experiencing any symptoms or have questions regarding magnets in consumer electronics and the impact they may have on their implanted medical devices.

A newly published study by scientists at the FDA supports the agency's recommendation. The investigators tested the magnetic field output of all iPhone 12 and Apple Watch 6 models at varying distances from the devices. They found that all the devices have static magnetic fields significantly greater than 10 G in close proximity, high enough to place implanted cardiac devices into magnet mode. They also found that when a separation distance of 6 inches or more is maintained, the phones and watches will not trigger magnet mode.

Mark’s Comments:

This should qualify as a nominee for the “you just can’t make this stuff up” category. Not sure if we now have to designate the “smart phone” as a medical device, a potentially lethal weapon, or both. In any case, it is important to be sure your patients who have an implanted device or have a family member who does are aware of this, particularly as many who have been physically distancing start to regather.


  • FDA. Magnets in Cell Phones and Smart Watches May Affect Pacemakers and Other Implanted Medical Devices. 13 May, 2021. Link
  • Seidman S, et al. Static magnetic field measurements of smart phones and watches and applicability to triggering magnet modes in implantable pacemakers and implantable cardioverter-defibrillators. Heart Rhythm. Published online 25 August, 2021. Link


Mark and John

Carilion Clinic Department of Family and Community Medicine

Feel free to forward Take 3 to your colleagues. Glad to add them to the distribution list.

Email: mhgreenawald@carilionclinic.org