Flu Advisory Accompanied by
a Drug Warning

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The popular analgesic and fever-reducer is not an NSAID—i.e., it does not have anti-inflammatory properties. It is the most commonly available pain-relieving and fever-reducing medication in part because it doesn't cause the stomach upset (or worse, bleeding risk) that NSAIDs occasionally can. But too much acetaminophen puts people at risk for a serious complication nonetheless: acetaminophen-induced liver toxicity.

It's worth noting that the dose at which potential toxicity occurs (8,400 mg) is dramatically higher than the amount that most adults need to effectively treat their symptoms (650 to 1,000 mg).

The real trouble lies in the fact that it's not always easy to notice that acetaminophen is an active ingredient in a combination medication unless you read the label carefully. For example, NyQuil, Theraflu, and Percocet (oxycodone with acetaminophen) all contain it. Unwittingly using multiple products that contain acetaminophen, then, can result in potential liver damage.

This is because acetaminophen is primarily processed in the liver. The liver breaks down most of the acetaminophen in a normal dose and eliminates it in the urine. But a small portion of the drug is converted to a byproduct that is toxic to the liver cells. If you take too much acetaminophen, whether all at once or over several days, the product can build up and cause liver damage.

In addition, there is some evidence that people with dehydration from vomiting or diarrhea, persistent fevers or underlying liver problems may be at slightly increased risk of liver damage when taking normally safe doses of acetaminophen. The resulting symptoms can be mistaken for a worsening flu illness instead of properly recognized as warning signs of liver damage.

This is one of the reasons the recommended maximum daily dose of acetaminophen in adults has decreased from 4,000 mg (two extra-strength tablets four times daily) to 3,000 mg since the original preparation became available. Taking two pills more than three times in one day is no longer advisable.

Still, 2015 research suggests that the safety margin may be even narrower. One study, using chip technology to produce a device that mimics a human liver, found that acetaminophen stops cellular respiration even at therapeutic doses, below the threshold of acetaminophen toxicity. Cellular respiration is the critical process by which cells convert nutrients into energy and also release waste.

Acetaminophen as a flu remedy?
While acetaminophen is a safe and effective analgesic generally, viral illnesses such as the common cold and flu generally get better on their own with rest, fluids and time. One recent randomized, controlled trial found that acetaminophen is not effective in treating influenza. There was no difference in symptom scores, body temperature, time to illness resolution or overall health status between subjects who took the drug and those who did not. In any case, be sure to always read the label of any cough, cold or pain medication carefully for the amount of acetaminophen in the drug so that you don’t inadvertently take too much.

Acetaminophen aside, the CDC reports that this season's vaccine is offering significant protection against circulating viruses. They recommend an annual flu vaccine for everyone six months of age and older.

2016 flu vaccine nearly 60% effective
According to data presented at the CDC's Advisory Committee on Immunization Practices, the 2015-16 influenza vaccine is 59% effective so far. When broken down by virus type, the estimated effectiveness is 51% against the H1N1 viruses causing most influenza this season, 76% against all influenza B viruses, and 79% against the B/Yamagata lineage of B viruses.

Flu activity started slowly this year, not becoming elevated until mid-January. Activity has continued to rise and the upswing is likely to continue for a month or more. If you have not already been vaccinated, it might be worth it given this season's surprisingly debilitating flu strains making their rounds among American schools, offices, malls, churches, theaters, public transportation systems and everywhere else people gather in groups.

Harvard Health Blog, Jan. 2016, Cold and Flu Warning by Susan Farrell, MD, http://tinyurl.com/zdf5ot5 with comments from Dr. Ann Bauer

FDA, Acetaminophen Overdose and Liver Injury,
Materials/Drugs/ DrugSafetyandRiskManagementAdvisoryCommittee/UCM164897.pdf

Respirology, 2016, Vol. 21 No. 2, pp. 370-377, http://www.ncbi.nlm.nih.gov/pubmed/26638130

CDC Health Advisory, 2016, Flu Season Begins: Severe Influenza Illness Reported, http://emergency.cdc.gov/han/han00387.asp

CDC Situation Update, Summary of Weekly FluView Report, Feb. 2016, http://www.cdc.gov/flu/weekly/summary.htm

CDC, Feb. 2016, Flu Vaccine Nearly 60 Percent Effective, http://www.cdc.gov/media/releases/2016/flu-vaccine-60-percent.html

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