Remarkably, with the exception of anaesthetic gases, the ancient human practice of inhaling substances into the lungs for systemic effect has only just begun to be adopted by modern medicine. Treatment of asthma by inhaled drugs began in earnest in the 1950s, and now such 'topical' or targeted treatment with inhaled drugs is considered for treating many other lung diseases. More recently, major advances have led to increasing interest in systemic delivery of drugs by inhalation. Small molecules can be delivered with very rapid action, low metabolism and high bioavailability; and macromolecules can be delivered without injections, as highlighted by the recent approval of the first inhaled insulin product. Here, we review these advances, and discuss aspects of lung physiology and formulation composition that influence the systemic delivery of inhaled therapeutics.

Inhaling medicines: delivering drugs to the body through the lungs

Particles incorporating a surfactant and/or a hydrophilic or hydrophobic complex of a positively or negatively charged therapeutic agent and a charged molecule of opposite charge for drug delivery to the pulmonary system, and methods for their synthesis and administration are provided. In a preferred embodiment, the particles are made of a biodegradable material and have a tap density less than 0.4 g/cm3 and a mass mean diameter between 5 νm and 30 νm, which together yield an aerodynamic diameter of the particles of between approximately one and three microns. The particles may be formed of biodegradable materials such as biodegradable polymers. For example, the particles may be formed of poly(lactic acid) or poly(glycolic acid) or copolymers thereof. Alternatively, the particles may be formed solely of a therapeutic or diagnostic agent and a surfactant. Surfactants can be incorporated on the particule surface for example by coating the particle after particle formation, or by incorporating the surfactant in the material forming the particle prior to formation of the particle. Exemplary surfactants include phosphoglycerides such as dipalmitoyl phosphatidylcholine (DPPC). The particles can be effectively aerosolized for administration to the respiratory tract to permit systemic or local delivery of wide a variety of therapeutic agents. Formation of complexes of positively or negatively charged therapeutic agents with molecules of opposite charge can allow control of the release rate of the agents into the blood stream following administration.

Preparation of particles for inhalation

Improved aerodynamically light particles for delivery to the pulmonary system, and methods for their preparation and administration are provided. In a preferred embodiment, the aerodynamically light particles are made of a biodegradable material and have a tap density less than 0.4 g/cm3 and a mass mean diameter between 5 µm and 30 µm. The particles may be formed of biodegradable materials such as biodegradable polymers. For example, the particles may be formed of a functionalized polyester graft copolymer consisting of a linear .alpha.-hydroxy-acid polyester backbone having at least one amino acid group incorporated therein and at least one poly(amino acid) side chain extending from an amino acid group in the polyester backbone. In one embodiment, aerodynamically light particles having a large mean diameter for example greater than 5 µm, can be used for enhanced delivery of a therapeutic or diagnostic agent to the alveolar region of the lung. The aerodynamically light particles optionally can incorporate a therapeutic or diagnostic agent, and may be effectively aerosolized for administration to the respiratory tract to permit systemic or local delivery of wide variety of incrorporated agents.

Aerodynamically light particles for pulmonary drug delivery

Aerodynamically light particles incorporating a surfactant on the surface thereof for drug delivery to the pulmonary system, and methods for their synthesis and administration are provided. In a preferred embodiment, the aerodynamically light particles are made of a biodegradable material and have a tap density less than 0.4 g/cm 3 and a mass mean diameter between 5 μm and 30 μm. The particles may be formed of biodegradable materials such as biodegradable polymers. For example, the particles may be formed of poly(lactic acid) or poly(glycolic acid) or copolymers thereof. Alternatively, the particles may be formed solely of the drug or diagnostic agent and a surfactant. Surfactants can be incorporated on the particle surface for example by coating the particle after particle formation, or by incorporating the surfactant in the material forming the particle prior to formation of the particle. Exemplary surfactants include phosphoglycerides such as L-α-phosphatidylcholine dipalmitoyl. The aerodynamically light particles incorporating a therapeutic or diagnostic agent and a surfactant may be effectively aerosolized for administration to the respiratory tract to permit systemic or local delivery of wide a variety of therapeutic agents.

Particles incorporating surfactants for pulmonary drug delivery

(D) Routes of delivery: Case studies

Inhaled therapeutic and diagnostic aerosols are examples of targeted delivery systems: they achieve high concentration in the respiratory tract (the usual target organ with these systems) while appearing in low concentrations in other parts of the human body. Development and use of inhalation aerosols requires an appreciation of the properties of these dynamic systems and the ways in which they interact with the anatomically and pathophysiologically complex human respiratory tract. The amounts of aerosol particles, or droplets, initially deposited at various sites in the respiratory tract will determine the intensity of local effects as well as the rate of clearance of these materials from the respiratory lumen. This activity can be modulated by suitable formulation intervention, such as presentation of the active agent in a slow releasing form carrier. Extension of duration of action of inhaled drugs by such means could be possible. As more discriminating methods for location of receptors and for the following of the fate of inhaled drugs and their carriers are becoming available, the ultimate potential for improvement of selective toxicity of agents used in pulmonary therapy by direct delivery into the respiratory tract can be critically evaluated.

Aerosols for delivery of therapeutic and diagnostic agents to the respiratory tract.

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Aerosols for delivery of therapeutic and diagnostic agents to the respiratory tract.