The pharmacokinetics of oral, single-dose, immediate-release riociguat 2.5 mg were characterized in two open-label, randomized, crossover studies in healthy males. In the first study, subjects pretreated for 4 days with once-daily omeprazole 40 mg received co-treatment with omeprazole + riociguat or riociguat alone (no pretreatment) on Day 5 (n=12). In the second study, subjects received co-treatment with 10 mL AlOH/MgOH + riociguat or riociguat alone (n=12). Pharmacokinetic characteristics were analyzed assuming log-normally distributed data. Safety and tolerability were also assessed.