Tiotropium bromide step-up therapy for adults with uncontrolled asthma. - Peters SP; Kunselman SJ; Icitovic N; Moore WC; Pascual R; Ameredes BT; Boushey HA; Calhoun WJ; Castro M; Cherniack RM; Craig T; Denlinger L; et al. (The New England journal of medicine, 2010)