Viagra and Cialis, the drugs used to treat impotency, may be associated with an increased risk of optic nerve damage in men with a history of heart attack or high blood pressure, suggests a small study in the British Journal of Ophthalmology.
Healthcare professionals prescribing these drugs should warn patients of the potential risk, say the authors.
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).
NAION is the most common form of optic nerve damage in older US adults, with up to 6000 people developing the condition every year. One in four will go on to develop it in both eyes.
The other half, who were randomly selected and did not have the condition, were used as a comparison group.
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.
The two groups were similar in terms of age, race, and lifestyle, and 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.
The authors led by Dr Gerald McGwin, Department of Ophthalmology, University of Alabama at Birmingham School of Medicine 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. The drugs may heighten the risk of NAION in those with vascular disease, who are already more susceptible, they explain. Non-arteritic anterior ischaemic optic neuropathy
(NAION) is the most common acute optic neuropathy
among older adults in the United States. An estimated 1500–6000 people develop NAION annually. It manifests as acute painless monocular vision loss, optic disc oedema, and a relative afferent pupillary defect. Presenting visual acuity is worse than 20/64
in about 50% of patients and may subsequently improve (in 30%–40% of patients), worsen (in 12%–22% of patients), or remain unchanged (in about 45% of patients).
Any patient who has endured a sudden severe loss of vision, and is prescribed Viagra or Cialis, should inform their healthcare practitioner first, say the authors. In fact there have been several case reports suggesting a link between certain phosphodiesterase inhibitor erectile dysfunction (ED) medications (Viagra (sildenafil) and Cialis (tadalafil)) and NAION. It is possible Viagra and Cialis may cause damage to the optic nerve head via its ability to increase nitric oxide levels
that in turn cause reduced perfusion. “However, this does not satisfactorily explain why we observed the strongest effect among those with a history of myocardial infarction or
hypertension,” say the authors. Insight regarding this issue can be gleaned
from the fact that certain chronic medical conditions such as hypertension, diabetes, heart disease, are thought to be risk factors for optic nerve head vascular insufficiency. The US FDA in a separate statement has this to say: while no link has been established between these medications and the occurrence of
NAION, it advises patients ‘‘…to stop taking these medicines, and call a doctor or healthcare provider right away if they experience sudden or decreased vision loss in one or both eyes. Further, patients taking or considering taking
these products should inform their health care professionals if they have ever had severe loss of vision, which might reflect a prior episode of NAION. Such patients are at an increased
risk of developing NAION again.’’
An accompanying editorial points out that some patients with impaired eyesight as a result of NAION have reportedly decided to sue Pfizer, the manufacturers of Viagra.
The editorial goes on to say that Pfizer have stated that there were no reports of NAION in the trials of the drug carried out before it was licensed, and 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.
But the editorial says that doctors may not be asking patients diagnosed with NAION whether they take Viagra or Cialis. ” While only a
small percentage of patients over 40 years
of age who have small cup to disc ratios
will ultimately develop NAION (regardless
of EDD use), eye care providers could
easily screen patients who are concerned
about this optic nerve anatomical risk
factor. The report by McGwin et al
suggests that vascular risk factors, such
as history of myocardial infraction or
ischaemic heart disease, are also important
issues to consider in assessing
possible risk for NAION in association.”
In his editorial comment,Dr Gerald McGwin,
Jr,University of Alabama at Birmingham Department of Ophthalmology advises, “given the results of the current study, patients with a history of myocardial infarction or hypertension who are prescribed Viagra or Cialis should be warned about the elevated risk of NAION associated with the use of these medications.”
