Whole finger iontophoresis of sodium nitroprusside to increase blood flow in patients with systemic sclerosis: Influence of concentration.

Iontophoresis of sodium nitroprusside increases finger blood flow in patients with systemic sclerosis, a multisystem connective tissue disease. Our aim was to examine the influence of dose, as a first step in exploring a possible new therapeutic approach. Ten patients with SSc and nine healthy controls were recruited. Blood flow in a single finger was assessed using laser Doppler imaging following iontophoresis of sodium nitroprusside at 'doses' of 2, 1, 0.5 and 0%. Graphs of perfusion over time (30min) were produced for each dose and from these curves, summary measures of response were calculated (area under curve/baseline and maximum perfusion/baseline. These measures were subject to regression analysis to investigate the effect of dose on response and to consider whether response differed between patients and healthy controls. Individual responses to altering the dose of iontophoresed sodium nitroprusside were highly variable but there was evidence to suggest increased response at doses of 0.5 and 1% (but not at 2%) compared to 0% for both area under curve/baseline (p=0.028 and p=0.011 respectively) and maximum perfusion/baseline (p=0.001 and p=0.002 respectively). There was no evidence that responses differed between patients and controls. Therefore the optimal dose for sodium nitroprusside iontophoresis is likely to be around 1%.