Development and Optimization of a Co-Spray-Dried Dry Powder Inhaler Co-Delivering the AntimicrobialPeptide KAMP-18 and Theophylline for Multifunctional Management of Bacterial Pulmonary Infections: Formulation Design, Physicochemical Characterization, Aerosol Performance, Molecular Modeling, Pharmacological Evaluation, and Preclinical Assessment

Every year, millions of people around the world struggle with severe lung infections caused by bacteria that have learned to resist standard antibiotics. These infections are particularly dangerous for those with chronic breathing conditions, where the airways become inflamed and narrowed, trapping bacteria in thick mucus and allowing them to form tough, protective communities called biofilms. Treating these cases requires a two-pronged approach: killing the bacteria and opening the airways so the medicine can reach them. However, delivering powerful new drugs directly to the deep lungs without them breaking down or causing harm has remained a difficult engineering challenge.

In this context, researchers at Cairo University have developed a new type of dry powder inhaler designed to tackle both problems at once. The device delivers a combination of two distinct substances: a specialized peptide, which is a small chain of amino acids that acts like a natural antibiotic, and a well-known medication called theophylline, which relaxes the muscles around the airways and calms inflammation. By using a process that sprays a liquid mixture into hot air to create tiny, dry particles, the team created a powder that can travel deep into the lungs, stay there longer, and work effectively against stubborn bacterial infections.

The journey began with the design of the powder itself. The researchers needed to ensure the particles were small enough to bypass the throat and settle in the deepest parts of the lungs, yet large enough to avoid being exhaled immediately. They used a computer-guided experimental method to test different temperatures and flow rates, eventually finding the perfect recipe. The resulting powder consists of microscopic spheres with a bumpy, wrinkled surface. This texture is not accidental; it was engineered by adding a specific amino acid that rises to the surface of the drying droplets, creating a rough exterior that prevents the particles from sticking together. This roughness allows the powder to flow smoothly out of the inhaler and disperse easily when the patient breathes in.

Once the powder was created, the team put it through a rigorous series of tests to see if the heat and pressure of the manufacturing process had damaged the delicate ingredients. They found that the antimicrobial peptide remained intact and fully active, retaining its ability to recognize and attack bacterial cells. Similarly, the theophylline survived the process without losing its ability to relax airway muscles. When tested in a lab setting that mimics human breathing, the powder performed exceptionally well. More than 90 percent of the medicine was released from the inhaler, and nearly 80 percent of that dose consisted of particles small enough to reach the deep lung tissue where infections often hide.

The effectiveness of the treatment was then measured against some of the most difficult-to-treat bacteria, including strains of Pseudomonas aeruginosa, Klebsiella pneumoniae, and methicillin-resistant Staphylococcus aureus. The results showed that the powder killed these bacteria just as effectively as the raw peptide did on its own. Perhaps even more impressively, the formulation was able to break down mature bacterial biofilms, reducing the total amount of bacterial mass by nearly 90 percent in some cases. This is a significant finding because biofilms often act as shields, protecting bacteria from conventional antibiotics and allowing infections to persist for years.

Beyond killing bacteria, the treatment demonstrated a powerful ability to soothe the inflamed lung tissue. In laboratory studies using lung cells, the combination of the two drugs worked together to restore the activity of a specific enzyme that helps turn off the body's inflammatory response. This led to a sharp decrease in the chemicals that cause swelling and damage in the lungs. The researchers also observed a synergistic effect on the airways: when the two drugs were delivered together in the powder, they relaxed the airway muscles much more effectively than either drug could alone, suggesting that the combination offers a greater therapeutic benefit than the sum of its parts.

Safety was a primary concern throughout the development. The researchers tested the powder on human lung cells and found that it was well-tolerated, causing no significant damage even at high concentrations. They also checked how the body handles the drugs after inhalation. The antimicrobial peptide stayed in the lungs for a prolonged period, maintaining a level high enough to kill bacteria for up to twelve hours, while the theophylline was absorbed into the bloodstream quickly to provide immediate relief for breathing. Crucially, the peptide did not cause damage to red blood cells, and repeated exposure to the powder in animal studies did not lead to inflammation or scarring in the lung tissue.

The study concludes that this co-spray-dried powder represents a promising new strategy for managing severe respiratory infections. By combining a potent, biofilm-breaking antibiotic with an anti-inflammatory bronchodilator in a single, stable, and deep-reaching powder, the researchers have created a tool that addresses the complexity of chronic lung disease. While further testing in infected animals and eventually in humans is needed to confirm these results, the work provides a strong foundation for a treatment that could help patients breathe easier while clearing infections that have long resisted standard care.