How do you counsel patients on the use of topical nitroglycerin for Raynaud's?

I am actually not a big fan of topical NTG for Raynaud phenomenon. We know that there is some significant systemic absorption and patients may have high rates of side effects (such as headache). These rates were as high as 30% in some of the studies, which I think is higher than we see with use of other vasodilators. When we do use it, we use 2% ointment and start low (like 1/2 inch) and divide amongst affected digits 2 times a day. Recall that patients cannot take this if they are on PDE5 inhibitors due to hypotension risk and you still need to be cautious with patients with low BP.