Pilot Speak: The Silent Killer

Runny nose, irritated and watery eyes, sneezing and general stuffiness are symptoms we all experience from time to time. These symptoms result from the release of a chemical called histamine from specific cells of our immune systems as a response to an external irritant or allergen. Histamine has many physiologic effects, including dilating blood vessels, making the walls of capillaries more permeable and being generally responsible for most of the symptoms associated with inflammation. Significantly, histamine is also found in the brain, and among other things, inhibits sleepiness. Because these symptoms are so common, it is not surprising that many of us routinely use a class of medications, antihistamines, to relieve our misery when those symptoms appear. So what does any of this have to do with pilots? As you’ll see, plenty. A few years ago, I was part of a group that assisted in analyzing all the fatal accidents of a specific aircraft model, with the aim of finding “root causes.” We weren’t interested in, for example, that a pilot lost control on approach, but rather, what factors may have made a loss of control more likely.

One of the interesting and disconcerting findings of our study was that a surprising number of accident pilots, 21 percent, had a variety of unauthorized drugs in their system – legal, illegal, prescription and over the counter (OTC). We wondered whether these specific pilots were unique, or whether there was an already known association with fatal accidents and the presence of drugs in the blood of the accident pilots. A literature search led me to a series of articles from the Civil Aerospace Medical Institute – a branch of the FAA. These articles analyzed the results of toxicology studies on pilots killed in aircraft accidents over several five-year periods. The most recent study analyzed fatalities from 2004-2008 and compared the findings with those of the prior studies.¹ All pilots killed in aviation accidents during that time period had their blood analyzed for the presence of Controlled Dangerous Substances (CDS), Schedules I-II (these include heroin, LSD, marijuana, ecstasy codeine cocaine, morphine, Demerol, Dexedrine, Ritalin and hydrocodone); Controlled Dangerous Substances, Schedules III-V, (including pain killers with less than 90 mg of codeine per tablet, cough medications with less than 200 mg of codeine/100 ml, Xanax, Darvocet, Valium, Ambien and Lomotil); Prescription Drugs, Nonprescription Drugs and alcohol (which was considered positive only if it was found above the FAA limit of 0.04 percent). The results were compared with the results of the previous studies. The breakdown of the percentage of pilots with positive toxicology findings is shown in Table 1.

As you can see, the percentage of pilots who died in aviation accidents and were found to have Controlled Dangerous Substances or alcohol in their system remained fairly constant over the series of studies. The number of pilots found to have prescription medications rose continually. There was no information presented in this study to suggest that the presence of these drugs was in any way related to the accident sequence. It may simply be that as pilots age and require medication for conditions like hypertension, blood lipid control, etc., more of them are on prescription medications. There was no effort made to distinguish between prescription medications that were authorized (the drugs were approved by the FAA and listed on the pilot’s FAA medical application) and those that were not. Interestingly, the most common drug found on the toxicology screens was diphenhydramine (Benadryl) which was found in 6.1 percent of the dead pilots. Diphenhydramine is available as a prescription medication, as well as over the counter, and in the FAA study was listed as a prescription medication. This listing of diphenhydramine as a prescription drug can also, at least partially, explain the apparent significant percentage of accident pilots on prescription medications versus nonprescription OTC preparations.

Table 1: A breakdown of the percentage of pilots with positive toxicology findings in fatal accidents.

The finding of diphenhydramine in the blood of accident pilots is of very real concern. Diphenhydramine is a first generation antihistamine – a drug that counters the effects of histamine. Of significance is that diphenhydramine crosses the blood brain barrier and therefore counteracts the effects of histamine in the brain. Remember that in the brain, histamine impairs sleep and in doing so promotes alertness. Diphenhydramine therefore, in addition to calming the symptoms of colds and allergies, is also a fairly potent sedative, and, in fact, is used in a significant number of OTC sleep medications. What’s worse is that the effects of diphenhydramine last longer than most pilots might think. In an interesting study done at the University of Iowa’s driving simulator,² driving abilities under the influence of different medications were monitored in four similar groups of drivers. One group, the placebo group, was medicated with a nonpharmacologically active agent, the second group was given alcohol sufficient to raise the blood alcohol concentration to 0.1 percent (legally impaired in all states), the third group was given 50 mg of diphenhydramine and the fourth group got a second generation antihistamine (fexofenadine, trade name Allegra™) which does not cross the blood brain barrier and therefore is non-sedating. The results of this study should give pause to all pilots who think OTC medications are safe to use when flying. The groups taking fexofenadine or placebo performed similarly and performed all driving tasks satisfactorily. The alcohol group performed significantly worse in tasks such as lane keeping, maintaining a specified distance from a preceding automobile and response time to avoiding a lane blocking vehicle. The diphenhydramine treated drivers performed uniformly worse than the alcohol impaired drivers, indicating that even relatively small doses of diphenhydramine affects driving ability more than an alcohol level consistent with the legal definition of drunk driving. Also of note is that there was no correlation between a feeling of drowsiness and driving ability in the diphenhydramine group. Meaning the diphenhydramine drivers performed poorly regardless of whether they felt drowsy or fully alert.

Diphenhydramine can be a silent killer. It is important for pilots to be very careful about any medications they take. For prescription drugs, check with your doctor and AME to ensure they are compatible with safe flying. For OTC medications, consider that if you feel poorly enough to take something, you probably shouldn’t be flying at all. If you do choose to fly when taking OTC medications, read the list of ingredients and be especially aware of drugs with sedating effects including pain killers, first generation antihistamines, sleep aids or anything with codeine or hydrocodone (many cough preparations). If there is any question, consult your physician or AME. If an OTC preparation contains a caution not to use the drug while operating dangerous machinery, consider that an airplane is potentially a very dangerous machine. Also note that the FAA recommends you wait until at least five times the interval between the recommended dosing interval has passed after you stop taking an OTC medication until you fly. For example, if the recommended dose is one tablet every 12 hours, wait 60 (12  5) hours from your last dose until you advance the throttle. This issue is real. Many OTC (and prescription) medications can significantly impair your ability to fly your aircraft safely. The accident statistics speak for themselves. For an excellent overview of the issue of drugs and aviation safety, the NTSB has produced a document that I encourage all pilots to review.³ As they say, the life you save may be your own.

NOTES:

1) Canfield, Dennis V., et.al. Drugs and Alcohol in Civil Aviation Accident Pilot Fatalities From 2004-2008. FAA Aeromedical Institute. 2011. https://www.faa.gov/data_research/research/med_humanfacs/ oamtechreports/2010s/media/201113.pdf

2) Weiler, JM et.al. Effects of fexofenadine, diphenhydramine, and alcohol on driving performance. A randomized, placebo-controlled trial in the Iowa driving simulator. Annals of Internal Medicine; 2000 Mar 7;132(5):35463. Abstract available at: http://www.ncbi.nlm.nih.gov/pubmed/10691585

3) Drug Use Trends in Aviation: Assessing the Risk of Pilot Impairment: NTSB Safety Study 14/01. http://www.ntsb.gov/safety/safety-studies/ Documents/SS1401.pdf