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The report, published Feb. 7 in The Journal for Nurse Practitioners, included two middle-age women with long COVID, a condition also known by the medical term "post-acute sequelae of COVID-19" (PASC). After catching COVID-19 in 2020, the women developed a slew of symptoms that lingered for many months after their initial infections had cleared; these long-lasting symptoms included cognitive impairment, skin rashes and bruising, chest pain and profound fatigue.
At some point, many months after first developing these symptoms, both individuals took antihistamines for unrelated allergies. They found that, unexpectedly, their long COVID symptoms improved after they took the drugs.
Both individuals now take a daily regimen of antihistamines and have said they've nearly regained their pre-PASC level of functioning, according to the case report.These two anecdotal reports align with the results of a larger study, published Oct. 5, 2021 in The Journal of Investigative Medicine, which included 49 long COVID patients.
Of these patients, 26 were given antihistamines. Of these, 19 reported complete or partial resolution of their symptoms. By comparison, only six of the other 23 patients, who were not given antihistamines, reported improved symptoms in the same time period.
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Overall, between mid-March 2020 and mid-July 2021, Survivor Corps members mentioned using antihistamines on the group's Facebook page more than 900 times, Lambert and her colleagues calculated. To gain more insight into these anecdotal reports, the team decided to zoom in on two Survivors' accounts.
The first patient likely became infected with COVID-19 in early January 2020, before diagnostic tests would have been available, the researchers reported. During her initial illness, she developed profound fatigue, fever, dry cough, chest pain, ulcers in her mouth and skin rashes on her torso, among other symptoms. Most of these symptoms resolved within 24 days, but some, like the rashes and chest pain, persisted.
Over the following weeks and months, new symptoms began to emerge, including cognitive impairment and pinpoint bruising on the arms, legs and trunk. In addition, various symptoms that had previously disappeared returned in waves as the months wore on. In June 2020, about six months after her initial illness, the patient ate cheese, to which she has a known allergy. She promptly took the over-the-counter antihistamine Benadryl (diphenhydramine) to stave off an allergic reaction.
"So she did not take this thinking, 'Oh, I'm taking this for long COVID symptoms.' Like she was never expecting to wake up and feel better," said Melissa Pinto, first author of the new case report and an associate professor of nursing at University of California, Irvine. However, the next day, the patient noticed she felt significantly less fatigued and better able to focus than the day before. These positive effects wore off over the following three days, so she tried taking Benadryl again. Again, her symptoms improved, and she continued taking the drug daily for the next six months.
One of her medical providers then prescribed Vistaril (hydroxyzine pamoate), a more potent antihistamine that's also used as an anti-anxiety medication. On a daily dose of the drug, "the patient had a nearly complete resolution of exercise intolerance, chest pain, fatigue, and brain fog," and her bruises, headaches and rashes steadily improved over time, the case report notes.
After nine months of treatment, she'd regained about 90% of her pre-PASC functioning, and she was able to fully return to work and regularly exercise, as she had prior to her infection.The second patient in the case report shared a similar story. She'd likely caught COVID-19 in March 2020, Pinto said. At the time, she tested negative for SARS-CoV-2 on a PCR test, but she then developed chills, shortness of breath and chest pain, and she received a clinical diagnosis of COVID-19 based on these symptoms. The patient went on to develop fever, joint pain and shortness of breath, as well as rapid heart rate, difficulty concentrating, abdominal pain, taste and smell loss and distinct rashes on her feet, known as "COVID toes."
Prior to catching COVID-19, the patient had seasonal allergies that she treated with Allegra (fexofenadine), a non-drowsy antihistamine. One day, she ran out of Allegra and used Benadryl instead. As an older, first-generation antihistamine, Benadryl can block histamines from plugging into receptors in the the brain; histamines help to regulate sleep and wakefulness, and by blocking this activity, Benadryl can cause drowsiness, Live Science previously reported.
However, after taking the drug, the patient noticed a marked improvement in her brain fog and overall fatigue. She began taking Benadryl daily and noted continued improvement in these symptoms; her abdominal pain also subsided and her senses of taste and smell returned.
She now takes Benadryl in the evening and Allegra in the morning, and on this regimen, she's regained about 95% of her pre-PASC functioning, the case report notes.