A phase I, randomized, proof‐of‐clinical‐mechanism study assessing the pharmacokinetics and pharmacodynamics of the oral <scp>PDE9A</scp> inhibitor <scp>BI</scp> 409306 in healthy male volunteers

BI 409306 increased rapidly in plasma and was subsequently detected in CSF, resulting in dose-dependent increases in cGMP levels in CSF. Results indicate BI 409306 efficiently crosses the blood-CSF barrier, with an acceptable level of AEs.