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1. Introduction
Viagra, a drug to treat impotence, may interfere with the ability to distinguish between blue and green, the two colours used at airports and in cockpit. Until Rules and Regulations for the use of Viagra by airmen have been issued, the Director: Civil Aviation advises pilots not to fly within 6 hours after using Viagra (sildenafil). The article: “Dangers of Viagra Use in Pilots” was published in the US Federal Air Surgeon’s Medical Bulletin-Fall 1998 and, is attached for information and further clarification. 2. Dangers of Viagra Use in Pilots
AMEs Should Become Familiar With the Detrimental Side-Effects of Sildenafil By Donalto J. Borrillo, MD, JD
Viagra(sildenafil citrate)
has recently received the Food and Drug Administration(FDA) seal of approval for
the treatment of male erectile dysfunction. The recent popularity of this medication and its availability to the
general aviation pilot, warrants a closer look by the aviation medical examiner(AME). With the pilot in mind,
the AME should become familiar with certain detrimental side effects of sildenafil.
To date, no written guidelines exist for the use of sildenafil and flying. Pursuant to the Guidelines for Aviation
Medical Examiners,
all medication use must be reported. However, the “as needed” use of sildenafil may
result in confusion for pilots. It is certainly conceivable, given “as needed” dosing and stigmata, that pilots
would not report sildenafil use. For the reasons outlined below, it is the author’s view that a minimum of 6
hours should pass from “as needed” dosing and flying. Furthermore, the continued (daily) use of Sildenafil is
incompatible with safe flight.
The AME should understand the mechanism of action for sildenafil. During sexual stimulation, nitric
oxide(NO) is released into the corpus cavernosum. Nitric oxide activates the enzyme guanylate cyclase,
thereby increasing the levels of cyclic guanosine monophosphate(cGMP). The cGMP produces smooth
muscle relaxation and the inflow of blood into the corpus cavernosum. Sildenafil enhances the effect of NO
by inhibiting phosphodiesterase Type 5(PDE5), which is responsible for degradation of cGMP in the corpus
When sexual stimulation releases NO, the inhibition of PDE5 by sildenafil increases levels of cGMP in the
corpus cavernosum This results in smooth muscle relaxation, inflow of blood to the corpus cavernosum and
sustained penile erection. Sildenafil at recommended doses has no effect in the absence of sexual
stimulation and has no direct relaxant effect on isolated human corpus cavernosum.
Index Page 2
Given the above mechanism of action, potential side effects include:
 Changes in colour vision
 Potentiation of nitrate medication
 Cockpit distraction
Sildenafil inhibits phosphodiesterae Type 5(PDE5), however, it also has an affinity and effect on
Phosphodiesterase Type 6(PDE6). PDE6 is a retinal enzyme involved in phototransduction. The inhibition of
PDE6 results in a mild transient dose related impairment of blue-green colour discrimination. Although only
3% of all patients report visual disturbances, this blue-green impairment could be dangerous during
Instrument Meteorological Conditions or night flying. The correct identification by the pilot of blue(1) and
green(2) is necessary for the safe flight. In addition, the use of colour video terminal displays has increased
in aviation and may present a problem in colour deficient pilot(3).
The AME should also be aware of sildenafil use in the “mile high club”(4). Sildenafil use by a pilot with
cardiac disease during sexual intercourse at 5,000 feet, could be deadly. Cardiac decease and nitrate use
are risk factors for sudden death during sexual intercourse, not to mention being medically disqualifying. The
hypotensive effect of nitrate(Isordil, SLNTG, etc.) is potentiated(5) by sildenafil, constant with its effect on the
NO/cGMP pathway. Recent deaths related to nitrates and sildenafil have made the combination an FDA
Finally, the initial dose of sidenafil is 50mg by mouth 1 hour prior to sexual activity. This dose can be
increased to 100mg and the drug is rapidly absorbed within 30 to 120 minutes(median 60 minutes).
Priapism is not a side effect; however, an early morning flight may be distracting. Full attention to instrument
scan and task at hand may be compromised by the 4-hour half-life of sildenafil. Metabolism of sidenafil by
the liver further decreases by 40% at age 65.
For the above reasons, “6 hours from Viagra to throttle” is recommended.
(1) Taxiway
(2) Tower
(3) The continued debate regarding “colour blindness” and the aviator is beyond the scope of this paper
(4) An activity not condoned by FAA, but known to occur
(5) A specific cause and effect has not been shown regarding sudden death
NOTE : Dr Borillo is the Commander, Flight Medicine at Wright-Patterson Air Force Base, Ohio.
The views expressed in this article are those of the author and not necessarily represent the official policy of
the Federal Aviation Administration Office of Aviation Medicine

The Federal Air Surgeon’s Medical Bul etin • Fall 1998


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