A Study of Single Doses of Frespaciguat (MK-5475) on Pulmonary Vascular Resistance (MK-5475-002)

In Part 1, one panel (Panel A) of up to 8 participants will dose in up to 3 dosing periods, with a minimum washout of 7 days between dosing periods. In each dosing period, 6 participants will receive frespaciguat and 2 will receive placebo, with 2 different participants receiving placebo in each of the dosing periods. Review of available safety data will occur prior to escalating to the next dose level. Participants from Part 1 may continue into Part 2, which will assess safety, tolerability, pharmacokinetics (PK) and pharmacodynamics (PD) of single-dose inhaled frespaciguat. Three additional panels of participants (Panels B, C and D) will be enrolled into Part 2. Participants in Panel A will participate in 2 open-label dosing periods to assess PD measures associated with right heart catherization (RHC) \[Period 2\] and functional respiratory imaging (FRI) \[Period 3\]. Participants in Panels B, C, and D will participate in 3 dosing periods: Period 1 (open-label assessment of safety/tolerability and PK), Period 2 (FRI period) and Period 3 (RHC period).