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Metformin + Viagra More Effective Treatment for Erectile Function

Posted: Wednesday, June 24, 2009

Insulin-resistant men had significant improvement in erectile function when metformin was added to sildenafil (Viagra), according to data from a small clinical study.  Metformin increases the activity of sildenafil.

Pablo Knoblovits, M.D., of Hospital Italiano de Buenos Aires in Argentina, reported at the Endocrine Society meeting that, sildenafil alone had failed to improve erectile function, and men who received a placebo in addition to the phosphodiesterase-5 (PDE5) inhibitor continued to have erectile problems,  "We think metformin potentiates the activity of sildenafil by improving insulin resistance and nitric oxide activity in the vascular endothelium of the penis."  

Dr. Knoblovits noted that, erectile function depends in large part on the release of nitric oxide by the vascular endothelium. Sildenafil and other PDE5 inhibitors improve erectile function by inhibiting the breakdown to nitric oxide.

Obesity, metabolic syndrome, and Type 2 diabetes all interfere with nitric oxide-mediated endothelial function. The three conditions are characterized by insulin resistance, which can interfere with PDE5 inhibitors' ability to prolong the effects of nitric oxide on penile vascular endothelium, Dr. Knoblovits continued.

In animal models of erectile dysfunction, the diabetes drug metformin improved erectile function.

To determine whether the drug has similar activity in humans, investigators studied 30 insulin-resistant men who had significant erectile dysfunction despite treatment with sildenafil. Dr. Knoblovits reported that 17 men used sildenafil on demand plus metformin 1,700 mg/day, and the remaining 13 used sildenafil and placebo.

Evaluations at baseline and after two and four months of treatment included calculation of body mass index and waist circumference; measurement of insulin and glucose; calculation of insulin resistance by homeostatic model assessment (HOMA); evaluation of adverse events; and evaluation of erectile function by means of the International Index of Erectile Function 5 (IIEF-5).

Baseline IIEF-5 score averaged 14.3 in the metformin group and 15.2 in the placebo group. At two months, the mean score had increased to 17 in the metformin group compared with a decline to 14.8 in the placebo group (P=0.01). After four months the mean IIEF-5 scores were 19.8 in the metformin group and 15.8 in the placebo group (P=0.001).

The improvement in erectile function in the metformin group coincided with significant improvement in HOMA compared with the placebo group at two and four months (P=0.01, P=0.04, respectively).

BMI and waist circumference also declined significantly at two and four months in the metformin group versus placebo (P=0.03 to P=0.003).

Practice Pearls:

Explain to patients that the diabetes drug improved erectile function in men who had not improved with sildenafil.

The study involved a small number of patients.

Note that this study was published as an abstract and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.

Source: Diabetes In Control: Knoblovits P, et al "Metformin improves erectile function in nondiabetic patients with insulin resistance and erectile dysfunction" J Clin Endocrinol Metab 2009; 94(6 suppl): Abstract P2-347.

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