In a randomized placebo-controlled study in 160 healthy volunteers, inhaled doses of iloprost solution were given either with a fixed dose of 2.5 micrograms iloprost 6 times daily (total daily dose of 15 micrograms), or beginning with 5.0 microgram and increasing up to 20 micrograms, or the highest tolerated dose for a total of 6 dose inhalations (total daily dose of 70 micrograms).