Aiming at the inhaled treatment of pulmonary diseases, the optimization process of the previously reported MAPI compound 92a is herein described. The project was focused on overcoming the chemical stability issue and achieving a balanced bronchodilator/anti-inflammatory profile in rats in order to be confident in a clinical effect without having to overdose at one of the biological targets. The chemical strategy was based on fine-tuning of the substitution pattern in the muscarinic and PDE4 structural portions of the dual pharmacology compounds, also making use of the analysis of a proprietary crystal structure in the PDE4 catalytic site. Compound 10f was identified as a chemically stable, potent, and in vivo balanced MAPI lead compound, as assessed in bronchoconstriction and inflammation assays in rats after intratracheal administration. After the in-depth investigation of the pharmacological and solid-state profile, 10f proved to be safe and suitable for development.