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Metformin appears to play a role in preventing long COVID when taken early during a COVID-19 infection, according to a new preprint study from The Lancet. The preprint hasn’t yet been peer-reviewed or published in a journal.
In particular, metformin led to a 42% drop in long COVID among people who had a mild to moderate COVID-19 infection.
“Long COVID affects millions of people, and preventing long COVID through a treatment like metformin could prevent significant disruptions in people’s lives,” says lead author Carolyn Bramante, MD, an assistant professor of internal medicine and pediatrics at the University of Minnesota.
Between January 2021 and February 2022, Bramante and colleagues tested three oral medications – metformin (typically used to treat type 2 diabetes), ivermectin (an antiparasitic), and fluvoxamine (an antidepressant) – in a clinical trial across the U.S. called COVID-OUT. The people being studied, investigators, care providers, and others involved in the study were blinded to the randomized treatments. The trial was decentralized, with no in-person contact with participants.
The researchers included patients who were ages 30-85 with overweight or obesity, had documentation of a confirmed COVID-19 infection, had fewer than 7 days of symptoms, had no known prior infection, and joined the study within 3 days of their positive test. The study included monthly follow-up for 300 days, and participants indicated whether they received a long COVID diagnosis from a medical doctor, which the researchers confirmed in medical records after participants gave consent.
The medications were pre-packaged into pill boxes for fast delivery to participants and to ensure they took the correct number of each type of pill. The packages were sent via same-day courier or overnight shipping.
The metformin doses were doled out over 14 days: with 500 milligrams on the first day, 500 milligrams twice a day for the next 4 days, and then 500 milligrams in the morning and 1,000 milligrams in the evening for the remaining 9 days.
Among the 1,323 people studied, 1,125 agreed to do long-term follow-up for long COVID, including 564 in the metformin group and 561 in the blinded placebo group. The average age was 45, and 56% were women, including 7% who were pregnant.
The average time from the start of symptoms to starting medication was 5 days, and 47% began taking the drug within 4 days or less. About 55% had received the primary COVID-19 vaccination series, including 5.1% who received an initial booster, before enrolling in the study.
Overall, 8.4% of participants reported that a medical provider diagnosed them with long COVID. Of those who took metformin, 6.3% developed long COVID, compared to 10.6% among those who took the identical-matched placebo.
The risk reduction for metformin was 42% versus the placebo, which was consistent across subgroups, including vaccination status and different COVID-19 variants.
When metformin was started less than 4 days after COVID-19 symptoms started, the effect was potentially even greater, with a 64% reduction, as compared with a 36% reduction among those who started metformin after 4 or more days after symptoms.
Neither ivermectin nor fluvoxamine showed any benefits for preventing long COVID.
At the same time, the study authors caution that more research is needed.
“The COVID-OUT trial does not indicate whether or not metformin would be effective at preventing long COVID if started at the time of emergency department visit or hospitalization for COVID-19, nor whether metformin would be effective as treatment in persons who already have long COVID,” they wrote. “With the burden of long COVID on society, confirmation is urgently needed in a trial that addresses our study’s limitations in order to translate these results into practice and policy.”
Several risk factors for long COVID emerged in the analysis. About 11.1% of the women had a long COVID diagnosis, as compared with 4.9% of the men. Also, those who had received at least the primary vaccine series had a lower risk of developing long COVID, at 6.6%, as compared with 10.5% among the unvaccinated. Only one of the 57 people who received a booster shot developed long COVID.
Notably, pregnant and lactating people were included in this study, which is important given that pregnant people face higher risks for poor COVID-19 outcomes and are excluded from most non-obstetric clinical trials, the study authors wrote. In this study, they were randomized to metformin or placebo but not ivermectin or fluvoxamine due to limited research about the safety of those drugs during pregnancy and lactation.
The results are now under journal review but show consistent findings from other recent studies. Also, in August 2022, the authors published results from COVID-OUT that showed metformin led to a 42% reduction in hospital visits, emergency department visits, and deaths related to severe COVID-19.
“Given the lack of side effects and cost for a 2-week course, I think these data support use of metformin now,” says Eric Topol, MD, founder and director of the Scripps Research Translational Institute and editor-in-chief of Medscape, WebMD’s sister site for health care professionals.
Topol, who wasn’t involved with this study, has been a leading voice on COVID-19 research throughout the pandemic. He noted the need for more studies, including a factorial design trial to test metformin and Paxlovid, which has shown promise in preventing long COVID. Topol also wrote about the preprint in Ground Truths, his online newsletter.
“As I’ve written in the past, I don’t use the term ‘breakthrough’ lightly,” he wrote. “But to see such a pronounced benefit in the current randomized trial of metformin, in the context of it being so safe and low cost, I’d give it a breakthrough categorization.”
Another way to put it, Topol wrote, is that based on this study, he himself would take metformin if he became infected with COVID-19.
Jeremy Faust, MD, an emergency medicine doctor at Brigham and Women’s Hospital in Boston, also wrote about the study in his newsletter, Inside Medicine. He noted that the 42% reduction in long COVID means that 23 COVID-19 patients need to be treated with metformin to prevent one long COVID diagnosis, which is an “important reduction.”
“Bottom line: If a person who meets criteria for obesity or overweight status were to ask me if they should take metformin (for 2 weeks) starting as soon as they learn they have COVID-19, I would say yes in many if not most cases, based on this new data,” he wrote. “This is starting to look like a real win.”
The Lancet (preprint): “Outpatient Treatment of COVID-19 and the Development of Long COVID Over 10 Months: A Multi-Center, Quadruple-Blind, Parallel Group Randomized Phase 3 Trial.”
Carolyn Bramante, MD, assistant professor of internal medicine and pediatrics, University of Minnesota.
Eric Topol, MD, founder and director, Scripps Research Translational Institute; editor-in-chief, Medscape.
Ground Truths: “A break from Covid waves and a breakthrough for preventing Long Covid.”
Inside Medicine: “Metformin found to reduce Long Covid in clinical trial.”
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