Scientists advance mechanism for Viagra-induced stroke and heart attack

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http://www.drugintel.com/news/a30113/viagra_causation.htm

 

 

Scientists advance mechanism for Viagra-induced stroke and heart attack

 

STRAFFORD Jan 13 2003 (DrugIntel) - The epidemiology of Viagra-(sildenafil-)

induced strokes has been controversial, and so far Pfizer has successfully

prevented cases from coming to trial. An additional mechanism to those already

identified emerged with the discovery that cyclic-GMP dependent protein kinase

(PKG) is required for the initiation of platelet aggregation by thrombin or von

Willebrand (vWF)factor. Sildenafil amplifies this effect through its well

known, universally accepted inhibition of phosphodiesterase (PDE) that normally

degrades CGMP: it is observed that platelets are supersensitive to thrombin and

vWF. This means that thrombus (clot) formation would begin in a patient on

Viagra. If the patient is at risk due to atherosclerosis or another condition,

a stroke or heart attack could well develop.

 

A press release was issued from University of Illinois at Chicago with the title

Viagra Deaths Explained By New Understanding Of Platelet Clumping, a similar

title run by Science Daily. BBC ran the item with somewhat more conservative

tone, Clue to mystery Viagra deaths.

 

Pfizer did not include on the Viagra label the 8 cardiovascular deaths in the

Viagra group (vs. 1 cancer death in the placebo group) that occurred in clinical

trials. The major rationale for FDA not requiring this information to be

reported appears to have been that the clinical investigators' believed there

was no mechanism to explain how sildenafil might cause such effects and thus the

investigational drug could not have been responsible. [CDER Viagra (sildenafil)

Joint Clinical Review NDA 20-895 Section 8, pp. 40-56, January 22, 1998]

 

Other mechanisms of action of sildenafil previously have been invoked to explain

the drug's ability to cause cardiovascular calamities:

opposing vasomotor actions through vasodilatation and its sympathetically-driven

vasoconstriction, opposing forces tending to rupture atherosclerotic plaques;

formation of thrombus on the newly exposed surface of plaqueswatershed effects

in the brain as demonstrated by 12% occurrence of headaches'cross-talk' by

inhibition of PDE 3 and causing heart attack by the same mechanism as milrinone

Concerning epidemiology -

 

More than half the deaths, or first symptoms leading to death, occur within 4

hours of using Viagra.

 

89% of deaths due to Viagra occur in individuals using the drug for the first

time, suggesting that some individuals are highly susceptible.

 

The death rate to users of other ED medications such as alprostadil is 20 times

lower than that of Viagra.

 

Lehmann J, 2001

 

 

 

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