Scientists map a decision framework for designing inhalable liposome medicines

Inhaled liposomal medicines have long promised a way to send drugs directly into the lungs while limiting the systemic exposure that plagues oral and injected therapies. Yet despite decades of work, only one inhaled liposomal product has reached patients: amikacin liposome inhalation suspension, approved for treatment-refractory Mycobacterium avium complex lung disease. A new structured narrative review, published in Pharmacia, argues that the field’s slow translation reflects a fragmented evidence base and proposes a remedy in the form of an eight-step decision framework that links every formulation choice to the pulmonary barrier it must overcome, the aerosol device that must deliver it, and the quality attributes needed to prove it works.

The review, which searched PubMed for English-language publications from 2021 to September 2026 and supplemented the results with targeted hand-searching of publisher and regulatory sources, ultimately drew on 62 cited sources. The authors were explicit about the limits of their approach: screening was performed by a single reviewer, exact counts of excluded records were not prospectively logged, and no formal risk-of-bias assessment was carried out. Instead, each of 18 illustrative experimental studies was graded on a four-level translational hierarchy, ranging from clinical evidence at Level 1 down to conventional in vitro characterization at Level 4. Fourteen of those studies provided direct conventional-liposome evidence; four were classified only as indirect mechanistic evidence drawn from related carriers.

That distinction matters, because the review’s central analytical move is to separate what can be transferred from lipid nanoparticles, lipoplexes, nanoemulsions, and cubosomes to conventional phospholipid-bilayer liposomes, and what cannot. Findings on aerosol generation, lipid-airway interactions, and general surface-chemistry effects may generalize across lipid-based carriers. But intracellular delivery, endosomal escape, ionizable-lipid chemistry, and nucleic acid encapsulation efficiency cannot be extrapolated directly, because lipid nanoparticles rely on internal architectures that differ fundamentally from liposomes. Observations derived exclusively from non-liposomal carriers were therefore retained only as indirect mechanistic evidence requiring direct confirmation in the intended liposomal system.

The framework itself is a sequential, hypothesis-generating process rather than an algorithm that predicts an optimal formulation. It begins with the therapeutic objective and payload, moves to the intended deposition site, then identifies the dominant pulmonary barrier—mucus, surfactant, epithelial transport, macrophage clearance, or intracellular trafficking. Only then are candidate formulation variables selected, followed by a compatible aerosol platform, the critical quality attributes and biological endpoints needed for verification, and finally experimental confirmation or reformulation. A key structural insight is that the aerodynamic diameter of the emitted droplet or particle, not the hydrodynamic diameter of the vesicle, governs regional deposition, so the intended site of action must be translated into a target aerodynamic size distribution before formulation variables are fixed.

Disease context determines whether a given pulmonary interaction helps or hurts. For intracellular infections, macrophage uptake may be part of the therapeutic objective rather than an unwanted clearance mechanism, so formulations that reduce cellular recognition—including strongly shielding PEGylation strategies—should not automatically be preferred. For extracellular targets or prolonged tissue residence, the same uptake may accelerate clearance or sequestration. Vesicle size, surface charge, PEGylation, and lipid composition are therefore disease- and objective-specific variables rather than universally beneficial characteristics, a conclusion the authors emphasize throughout their disease-specific applications to mucus-rich airway disease, pulmonary fibrosis, lung cancer, and respiratory infection.

The evidence on individual design variables is nuanced. In pulmonary cell models and artificial mucus, liposomes of approximately 100 nanometers showed greater colloidal stability, lower cytotoxicity, and more prolonged migration through artificial mucus than 600-nanometer vesicles, which showed greater mucus retention. But retention may also promote mucociliary clearance, and because artificial mucus may not reproduce the viscoelastic properties and biochemical heterogeneity of native mucus, the in vivo significance remains uncertain. The 100–200 nanometer range is described as a model-derived candidate requiring confirmation in disease-relevant or patient-derived mucus, not an established optimum.

Surface charge carries its own tolerability risks. In one study, RAW264.7 macrophage viability fell from 95.2 percent at a zeta potential of −2.5 millivolts to 69.3 percent at +21.5 millivolts, while hemolysis rose from 4.2 percent to 35.2 percent across the same span. Cationic surfaces should therefore be treated as a tolerability risk requiring explicit local pulmonary safety evaluation, with any targeting or pH-responsive strategy tested against a charge-matched non-targeted control. PEGylation presents a different trade-off: it may increase mucus transport and colloidal stability while reducing cellular uptake and even payload loading. In pirfenidone liposomes, adding 4 mole percent of a PEG-lipid shifted the surface charge sharply negative and lowered encapsulation efficiency from 45 percent to 27 percent and loading capacity from 8.9 percent to 6.6 percent, at an essentially unchanged particle diameter.

Aerosolization itself is a stress test. Nebulization and drying can compromise vesicle integrity, causing aggregation, leakage, or loss of drug activity, so size, polydispersity, encapsulation efficiency, and release must be measured both before and after actuation. Vibrating-mesh nebulizers may impose less mechanical stress than some jet nebulizers, but the review insists they remain a candidate platform to be selected by direct formulation–device comparison rather than assumed preferable. Dry powders and lyophilized liposomes improve stability and portability but can disrupt bilayers and increase drug leakage, requiring protective excipients and careful processing. The review’s quality-attribute tables also caution that commonly quoted development targets—such as a mass median aerodynamic diameter of roughly 1 to 5 micrometers or a fine particle fraction of at least 40 percent—appear in no regulatory or compendial guidance as cross-product acceptance criteria, and the only approved inhaled liposomal product reports an aerosol diameter of approximately 4.7 micrometers, above the range most often cited in the preclinical literature.

The clinical benchmark remains sobering. In the pivotal CONVERT trial, 65 of 224 patients receiving amikacin liposome inhalation suspension with guideline-based therapy achieved culture conversion by month 6, compared with 10 of 112 patients on guideline-based therapy alone, an odds ratio of 4.22, while respiratory adverse events were reported in 87.4 percent versus 50.0 percent of patients. The approved product pairs amikacin in dipalmitoylphosphatidylcholine and cholesterol liposomes with a dedicated vibrating-mesh nebulizer, demonstrating the feasibility of an integrated liposome–device product without predicting success for other formulations. Beyond this single precedent, evidence for pulmonary fibrosis, lung cancer, inflammatory disease, and nucleic acid delivery remains predominantly preclinical and model-dependent, with route differences often confounding comparisons between formulations.

The authors are candid that their decision chain is a literature-derived conceptual framework that has not been prospectively validated, and they propose a concrete test: applying it to three to five independent inhalable-liposome case studies spanning different payloads, indications, and aerosol platforms, documenting formulation choices and expected outcomes before experiments and comparing them with observed quality attributes. Agreement between predicted and observed profiles would indicate predictive accuracy and guide refinement. Until then, the framework’s value lies less in prescribing answers than in forcing developers to state, at every step, which barrier they are targeting, which device will carry the dose, and which measurements will confirm that the finished product behaves as designed—a discipline the review argues has been missing from a field rich in preclinical promise but thin on clinical delivery.

Subject of Research: A decision framework for designing inhalable liposomal drug formulations against pulmonary barriers

Article Title: Inhalable liposomes: a formulation decision framework linking design variables to pulmonary barriers, aerosol platforms, and critical quality attributes

Article References: Lupçi, V., Loshaj Shala, A., Lupçi, A., Bağcı, U., Basholli Salihu, M., & Kryeziu, T. (2026). Inhalable liposomes: a formulation decision framework linking design variables to pulmonary barriers, aerosol platforms, and critical quality attributes. Pharmacia, 73, Article e210129. https://doi.org/10.3897/pharmacia.73.e210129

Image Credits: AI Generated

DOI: 10.3897/pharmacia.73.e210129

Keywords: inhalable liposomes, pulmonary drug delivery, PEGylation, aerosolization, nebulization, critical quality attributes, amikacin liposome inhalation suspension, mucus penetration, lipid nanoparticles, dry powder inhaler, pulmonary fibrosis, narrative review