Impotency drugs such as Viagra
and Cialis may be associated with increased risk of damage
to the optic nerve in some men, research suggests.
US researchers found an increased risk
in men with a history of heart attack or high blood pressure.
The University of Alabama team said healthcare
professionals should warn patients of the potential risk.
The British Journal of Ophthalmology
study follows several reports linking the drugs to eyesight
problems.
The findings are based on 76 men attending
one US specialist eye clinic.
Half the men had optic nerve damage,
diagnosed as non-arteritic anterior ischaemic optic neuropathy
(NAION), the rest were free of the problem.
All the patients were asked about their
lifestyle, including smoking and alcohol intake, whether
they had been diagnosed with heart disease, diabetes,
or high blood pressure and prescribed treatment for these
conditions.
They were also asked if they had been
prescribed Viagra and Cialis for erectile difficulties.
Men with optic nerve damage were no more
likely to have taken the impotency drugs than men in the
comparison group.
But men who had had a heart attack were
10 times more likely to have optic nerve damage if they
had taken Viagra or Cialis before their diagnosis.
Men with high blood pressure were also
more likely to have optic nerve damage if they had taken
these drugs, although this was not statistically significant.
Blood flow
The authors caution that their study
is small, but suggest that the drugs may reduce the blood
flow to the anterior optic nerve, resulting in tissue
damage.
They believe the drugs may heighten the
risk of NAION in those with vascular disease, who are
already more susceptible.
The researchers urge any patient who
has endured a sudden severe loss of vision, and has been
prescribed Viagra or Cialis, to contact a doctor.
Writing in the journal, they said: "Though
NAION is a rare condition, the large number of men using
Viagra or Cialis suggests that, should an association
truly exist, the incidence of NAION could rise dramatically."
An editorial in the same journal points
out that some patients with impaired eyesight as a result
of NAION have reportedly decided to sue Pfizer, the manufacturers
of Viagra.
However, Pfizer has said there were no
reports of NAION in the trials of the drug carried out
before it was licensed.
The company also argued that a greater
number of cases related to this type of drug would have
been reported by now if the association was anything other
than coincidental.
Lilly ICOS, which manufactures Cialis,
said there had been a small number of cases of NAION in
people taking the drug.
This was now flagged up in the prescribing
information.
In a statement, the company said it was
difficult to establish a firm link as most patients taking
impotency drug had other risk factors which rendered them
potentially vulnerable to NAION.
