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Viagra causes significant retinal blood vessel dilation, study finds
A drug that opens up blood vessels could theoretically be used to treat patients with ischemic lesions or ischemic optic neuropathy.
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BASEL, Switzerland — Viagra causes significant dilation of retinal arteries and veins in healthy patients, according to the findings of a small study conducted here by researchers with the University Eye Clinic Basel. The clinical implications of the drug’s effect for ophthalmology are not yet known, the study authors said.
“What we have shown is that healthy vessels dilate. We do not know yet how diseased vessels would behave. Therefore, we do not know whether this increase in ocular perfusion is of benefit for some patients or even dangerous for others. For us, it was important to show that this drug has an effect on the eye and it needs further steps to see whether this is beneficial or even dangerous in some other conditions,” Josef Flammer, MD, one of the study investigators, told Ocular Surgery News.
The study
The researchers evaluated the diameter response of retinal vessels to a single 50-mg dose of sildenafil (Viagra, Pfizer) in 10 healthy subjects.
Baseline measurements of the retinal vessels were taken with the Retinal Vessel Analyzer (Imedos) 20 minutes after pupil dilation with tropicamide. Blood pressure and heart rate measurements were also taken.
Evaluations were done at 30, 60, 90 and 120 minutes following sildenafil administration.
The researchers found that the single dose of sildenafil caused a significant increase of 5.8% in retinal artery diameters above baseline value 30 minutes after administration (P < .001). At 60 minutes, this declined only slightly to 5.1%. However, artery diameter values did not differ significantly from baseline values at 90 and 120 minutes.
Vein diameters also significantly in creased by 5.8% above baseline values after 30 minutes and were maintained at 60 minutes. The vein diameters decreased to 3.7% at 90 minutes, and normalized back to baseline after 120 minutes.
The researchers also observed a mild but significant decrease in mean arterial blood pressure (P < .0015) as well as a statistically significant increase in heart rate (P < .0004).
IOPs did not change significantly from baseline.
Implications
According to the report, the 5.8% increase in vessel diameter should lead to a considerable increase in retinal blood flow if blood velocity is assumed constant. However, the authors wrote, it is completely unclear whether the vasodilatation of the large retinal arteries and veins leads to an increase of blood flow and whether it interferes with retinal autoregulation. The authors noted that an increase in blood velocity has been observed by other researchers.
Because the study included only young, healthy individuals with assumed intact retinal autoregulation, it is not clear whether sildenafil exerts a comparable effect in elderly patients with concomitant cardiovascular disease, the authors wrote.
Dr. Flammer said the drug needs to be evaluated to see what happens in older patients who do have some circulatory problems in their eyes.
“For example, what happens with glaucoma patients? What happens in patients who have venous thrombus in the eye? What happens in diabetes patients? What happens in all these different situations? This needs to be clarified. What we have shown is that it has an effect. But when it is dangerous and when it might even be beneficial in some conditions, we don’t yet know,” he said.
According to the report, there was a mild drop in systemic blood pressure and a slight increase in heart rate that accompanied the vasodilation of the retinal vessels. The authors wrote that dilation of the retinal vessels could be expected when a drop in systemic blood pressure occurs. However, they wrote, it is unlikely that the dilation observed can be attributed to the mild decrease in blood pressure.
Theoretical applications
Dr. Flammer said any drug that dilates vessels can theoretically be useful in situations where there is reduced circulation.
“For example, if you have an ischemic lesion or an ischemic optic neuropathy, something like that, if you would have a drug that opens up these vessels, theoretically it would be of benefit. But it could also be the other way around,” he said.
He said it is doubtful the drug in its current form could be used to treat any conditions anyway.
“The drug is not designed for that.” He said. “One problem, for example, is the half-life. If you would have a drug that is beneficial in the long term, you would need a drug that has a long half-life. But theoretically, it’s an interesting observation if you develop a drug from this class, at least [we know] it has an effect.”
In future studies, Dr. Flammer said he would like to evaluate whether blood flow is influenced, as well as what happens in older patients and those who have different diseases, such as systemic hypertension or diabetes.
“You see, a lot of diabetes patients take the drug because they have impotence more often. And so it’s very important to see what happens with blood flow in diabetes patients,” he said.
“At the moment we just can say [sildenafil] has a significant influence, but we don’t know the clinical relevance of it,” he added.
For Your Information:
- Josef Flammer, MD, can be reached at the University Eye Clinic Basel, Mittlere Strasse 91, PO Box CH4012, Basel, Switzerland; (41) 61-265-8651; fax: (41) 61-265-8652; e-mail: josef.flammer@uhbs.ch. Dr. Flammer has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.
- Pfizer Inc., makers of sildenafil (Viagra), can be reached at 235 East 42nd St., New York, NY 10017; (212) 573-2323; Web site: www.pfizer.com. Imedos, makers of the Retinal Vessel Analyzer, can be reached at Schwanseestrasse 48, D-99423 Weimar, Germany; (49) 3643-59519; fax: (49) 3643-59518; Web site: www.imedos.de.
Reference:
- Pache M, Meyer P, et. al. Sildenafil induces retinal vasodilation in healthy subjects. Br J Ophthalmol. 2002;86:156-158.