Pulmonary delivery administers medication directly into the lungs through inhalation. This method uses the respiratory system as a pathway for drugs to reach the body, allowing them to exert either localized effects within the lungs or systemic effects after absorption into the bloodstream. Medicines are converted into an inhalable form, such as aerosols or fine powders, which patients then breathe in.
Understanding Pulmonary Delivery
The lungs are well-suited for drug administration due to their vast internal surface area, estimated at 100 to 140 square meters. This large surface comes from hundreds of millions of tiny air sacs, called alveoli. These alveoli are surrounded by a dense network of capillaries, and the barrier between air and blood is remarkably thin, about 0.2 to 0.7 micrometers.
After inhalation, drugs interact with this lung environment. Medications can act locally within the respiratory system to treat airway conditions, or they can be absorbed rapidly into the bloodstream for systemic distribution. Drug deposition in the lung depends on particle size. Particles 1 to 5 micrometers in diameter deposit in the small airways and alveoli. Those smaller than 0.1 micrometers are exhaled, while particles between 0.1 and 1 micrometer deposit in the alveoli and narrow conducting airways.
Advantages of Lung-Based Drug Delivery
Pulmonary drug administration offers several benefits. A primary advantage is the rapid onset of action, especially for systemic drugs. This quick effect occurs because the lungs’ rich blood supply allows direct absorption into the bloodstream, bypassing the digestive system and the liver’s first-pass metabolism, which can reduce drug effectiveness.
For local medications, such as those for asthma, pulmonary delivery can reduce systemic side effects. Delivering the drug directly to the affected airways achieves higher concentrations at the target site with lower overall body exposure, minimizing unwanted reactions. Pulmonary delivery is also a non-invasive method, meaning less patient discomfort and improved adherence to treatment compared to injections.
Devices and How They Work
Pulmonary drug delivery relies on specialized devices to convert medication into an inhalable form.
Metered-Dose Inhalers (MDIs)
Metered-dose inhalers (MDIs) are common devices that contain a pressurized canister of medicine. When the patient presses the canister, a pre-set amount of medicine is sprayed as an aerosol mist. Proper technique involves shaking the inhaler, exhaling completely, placing the mouthpiece, and pressing while slowly inhaling for 3 to 5 seconds, then holding the breath for about 10 seconds. Spacers, or holding chambers, can be attached to MDIs to improve drug delivery by holding the mist, making coordination easier and reducing deposition in the mouth and throat.
Dry Powder Inhalers (DPIs)
Dry powder inhalers (DPIs) deliver medication as a fine, dry powder. These devices are breath-actuated, meaning the patient’s forceful and deep inhalation releases the medicine. DPIs often require a specific procedure to load or prepare a dose. After exhaling fully away from the device, the patient inhales quickly and deeply for 2 to 3 seconds, holding their breath for approximately 10 seconds afterward. Unlike MDIs, DPIs do not use propellants and do not require a spacer.
Nebulizers
Nebulizers are machines that convert liquid medicine into a fine mist, allowing patients to breathe in the medication over a period of 5 to 20 minutes. The device consists of a compressor, tubing, a medicine cup, and a mouthpiece or mask. The compressor forces air into the liquid medicine, breaking it into an aerosol. Patients breathe normally through the mouthpiece or mask until the medicine cup is empty. Nebulizers are suitable for individuals who have difficulty using inhalers, such as young children or those with severe breathing issues, as they do not require specific inhalation coordination.
What Conditions Benefit from Pulmonary Delivery?
Pulmonary delivery is widely used for managing various respiratory conditions. Asthma, a chronic inflammatory respiratory disease, is commonly treated with inhaled medications that directly target affected airways to reduce inflammation and open air passages. Chronic obstructive pulmonary disease (COPD), involving persistent airflow limitation, also benefits from inhaled bronchodilators and corticosteroids to improve breathing and reduce flare-ups. Cystic fibrosis, a genetic disorder causing thick mucus buildup, utilizes inhaled medications like mucolytics and antibiotics to manage symptoms and infections.
Beyond respiratory diseases, pulmonary delivery has been explored for systemic drug effects, leveraging the lungs’ absorption efficiency. Inhaled insulin for diabetes management, though less common now, demonstrated rapid action. Some pain management and psychiatric medications have also been investigated for pulmonary delivery, aiming for rapid systemic entry and effect.