Increase in droxidopa intra-HD MAP were not significantly different from placebo , although droxidopa groups showed significant improvements in mean SBP after HD of +4.8 11.6 mm Hg ( 600-mg ) and +3.4 13.1 ( 400-mg ) compared with -4.4 17.9 mm Hg in placebo , and the drop seen in mean nadir SBP pre - to intra-HD was also reduced .