title: Iloprost-containing liposomes for aerosol application in pulmonary arterial hypertension: formulation aspects and stability.
abstract: OBJECTIVE
  Pulmonary arterial hypertension (PAH) is a severe and progressive disease. The prostacyclin analogue iloprost is effective against PAH, but requires six to nine inhalations per day. The feasibility of liposomes to provide a sustained release formulation to reduce inhalation frequency is evaluated from a technological point of view.
  
  
  METHODS
  Liposomal formulations consisting of di-palmitoyl-phosphatidyl-choline (DPPC), cholesterol (CH) and polyethyleneglycol-di-palmitoyl-phosphatidyl-ethanolamine (DPPE-PEG) were prepared. Their physico-chemical properties were investigated using dynamic light scattering, atomic force microscopy and differential scanning calorimetry. Stability of liposomes during aerosolization using three different nebulizers (air-jet, ultrasonic and vibrating mesh) was investigated with respect to drug loading and liposome size, pre- and post-nebulization.
  
  
  RESULTS
  The phospholipid composition affected the diameters of liposomes only slightly in the range of 200-400 nm. The highest iloprost loading (12 microg/ml) and sufficient liposome stability (70% drug encapsulation post-nebulization) was observed for the DPPC/CH (70:30 molar ratio) liposomes. The formulation's stability was confirmed by the relatively high phase transition temperature (53 degrees C) and unchanged particle sizes. The incorporation of DPPE-PEG in the liposomes (DPPC/CH/DPPE-PEG, 50:45:5 molar ratio) resulted in decreased stability (20-50% drug encapsulation post-nebulization) and a phase transition temperature of 35 degrees C. The vibrating mesh nebulizer offered a number of significant advantages over the other nebulizers, including the production of small aerosol droplets, high output, and the lowest deleterious physical influence upon all investigated liposomes.
  
  
  CONCLUSIONS
  Iloprost-loaded liposomes containing DPPC and CH components yield formulations which are well suited to aerosolization by the vibrating mesh nebulizer. The investigation of sustained release effects for the treatment of PAH in ex vivo and in vivo models is under way.
authors.affiliation: Department of Pharmaceutics and Biopharmacy, Philipps-University, D-35037 Marburg, Germany. elke_kleemann@gmx.de
authors.forename: Elke
authors.initials: E
authors.lastname: Kleemann
authors.forename: Thomas
authors.initials: T
authors.lastname: Schmehl
authors.forename: Tobias
authors.initials: T
authors.lastname: Gessler
authors.forename: Udo
authors.initials: U
authors.lastname: Bakowsky
authors.forename: Thomas
authors.initials: T
authors.lastname: Kissel
authors.forename: Werner
authors.initials: W
authors.lastname: Seeger
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine; D000280:Administration, Inhalation; D000336:Aerosols; D002152:Calorimetry, Differential Scanning; D002626:Chemistry, Pharmaceutical; D002784:Cholesterol; D004337:Drug Carriers; D004339:Drug Compounding; D004355:Drug Stability; D005079:Excipients; D006976:Hypertension, Pulmonary / Q000188:drug therapy*; D016285:Iloprost / Q000008:administration & dosage* / Q000627:therapeutic use*; D008081:Liposomes; D018625:Microscopy, Atomic Force; D009330:Nebulizers and Vaporizers; D010316:Particle Size; D011092:Polyethylene Glycols; D011650:Pulmonary Alveoli / Q000378:metabolism; D014465:Ultrasonics; D014665:Vasodilator Agents / Q000008:administration & dosage* / Q000627:therapeutic use*
chemical_list: D000336:Aerosols; D004337:Drug Carriers; D005079:Excipients; D008081:Liposomes; D014665:Vasodilator Agents; D015060:1,2-Dipalmitoylphosphatidylcholine; D011092:Polyethylene Glycols; D002784:Cholesterol; D016285:Iloprost