An Open Label, Dose Finding Trial of Viagra for the Treatment of Neuropathic Pain (in Diabetes Mellitus)

Neuropathic pain is a common problem resulting from a diverse group of disorders including nerve injuries and neuropathies related to diabetes and other disorders. Pharmacologic agents are available such as gabapentin, which can successfully treat many patients. For many however there is inadequate treatment available, due to lack of efficacy and poor tolerability and the need for new pharmacologic agents is recognized. We propose to study if sildenafil is effective in improving neuropathic pain, in patients with diabetes mellitus. Our primary outcome will be a reduction in the weekly average 11 point Likert pain scale (0 - no pain, 10 - worst possible pain) at 8 weeks. Secondary outcomes will include the Rand-36 quality of life scale, McGill visual analogue scale (VAS) and a sleep interference scale. This will be an open label study at 3 doses of sildenafil (25 mg, 50 mg and 100 mg). Patients will begin at 25 mg at night for 1 week. If pain continues, the dose will be increased to 50 mg at night for 1 week. If pain continues the dose will be increased to 100 mg at night. Subjects will be on the medication for 8 weeks. If this study suggests efficacy, the information will be used to plan a placebo controlled, double-blind study in the future. We propose to study if sildenafil is effective in improving neuropathic pain. Our primary outcome will be a reduction in the weekly average 11 point Likert pain scale (0 - no pain, 10 - worst possible pain) at 8 weeks. Secondary outcomes will include the Rand-36 quality of life scale, McGill visual analogue scale (VAS) and a sleep interference scale. This will be an open label study at 3 doses of sildenafil (25 mg, 50 mg and 100 mg). Patients will begin at 25 mg at night for 1 week. If pain continues, the dose will be increased to 50 mg at night for 1 week. If pain continues the dose will be increased to 100 mg at night. Subjects will be on the medication for 8 weeks. If this study suggests efficacy, the information will be used to plan a placebo controlled, double-blind study in the future.