Can Droxidopa be used for augmenting orthostatic hypotension treatment in patients who are already on midodrine and/or fludrocortisone?

I routinely combine droxidopa with fludrocortisone just as I would midodrine and fludrocortisone when orthostatic hypotension is refractory to tolerated doses of monotherapy. 

The use of droxidopa and midodrine is something I do less commonly, or frankly just rarely. They compete for the same receptors, after all. There is utility to combining them when a patient is generally refractory to midodrine, but benefits from droxidopa. Because droxidopa peaks at 2 hours after taking, some patients are really dragging until it kicks in. In a patient who is struggling for a significant period before it kicks in, sometimes taking midodrine with it (or an hour before it, even) may be helpful. It is trial and error, but it is an option in some patients. Usually, we only do this with the morning dose because BP rises throughout the day in patients with nOH. 

Strattera is an alternative adjunct with droxidopa as it blocks the reuptake of the NE generated from droxiodopa at the synapse.