http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2851459/Quote:
Suggested doses in various clinical studies (15,25) that exhibit beneficial activity of PDE inhibitors include sildenafil (Viagra) 50 mg twice daily, vardenafil (Levitra) 10 mg twice daily, and tadalafil (Cialis) 20 mg every two to three days, although further studies are needed to delineate optimal dosing suggestions.
So for the full dose, it might be taken every 2 - 3 days and you'd get the benefits of having it in your system.
http://www.ncbi.nlm.nih.gov/pubmed/16835313Quote:
Available evidence suggests that sildenafil may be associated with improved microcirculation, symptomatic relief, and ulcer healing in patients with secondary Raynaud's phenomenon. Limited information suggests similar effects with tadalafil and vardenafil. Improved blood flow and clinical improvements have also been observed in some patients with primary Raynaud's phenomenon treated with PDE5 inhibitors; however, studies have yielded conflicting results.
There has been research on the use of sildenafil for patients with Raynaud's phenomenon, which is sometimes secondary to MS, so something to consider for anyone who has Raynaud's as well.