title: Aminolevulinic acid-loaded Witepsol microparticles manufactured using a spray congealing procedure: implications for topical photodynamic therapy.
abstract: OBJECTIVE
  The aim was to enhance aminolevulinic acid (ALA) stability by incorporation into low-melting microparticles prepared using a spray congealing procedure and to evaluate temperature-triggered release, allowing topical bioavailability following melting at skin temperature.
  
  
  METHODS
  ALA-loaded Witepsol microparticles were prepared using a novel spray congealing technique. Entrapment efficiency was compared with conventional emulsion-based methods and modelled drug release profiles determined using a membrane separation technique. Raised receiver medium temperature was used to determine triggered release. Bioavailability and lipid-mediated enhancement of ALA penetration were determined in excised murine skin.
  
  
  RESULTS
  ALA-loaded Witepsol microparticles were spherical, with a mean diameter of 20 mum. Loading and stability studies demonstrated effective encapsulation, ranging from 91% to 100%, with no evidence of degradation to pyrazine derivatives. ALA release correlated with dissolution medium temperature, triggered at temperatures close to that of skin. Results suggested that molten Witepsol enhanced cutaneous permeation, whereas incorporation of microparticles in a semi-solid vehicle attenuated ALA penetration. Optimal use was direct application under occlusion.
  
  
  CONCLUSIONS
  Spray congealing is superior to the emulsion-based procedures with respect to encapsulation efficiency of ALA in Witepsol matrices, providing temperature-triggered release, enhanced stability and improved penetration of ALA through keratinised skin. These features could improve ALA delivery to superficial lesions as part of photodynamic therapy.
authors.affiliation: School of Pharmacy, Queen's University Belfast, Medical Biology Centre, Belfast, UK.
authors.forename: Rasil
authors.initials: R
authors.lastname: Al-Kassas
authors.forename: Ryan F
authors.initials: RF
authors.lastname: Donnelly
authors.forename: Paul A
authors.initials: PA
authors.lastname: McCarron
mesh_terms: D000287:Administration, Topical; D000622:Aminolevulinic Acid / Q000008:administration & dosage / Q000493:pharmacokinetics*; D000818:Animals; D004337:Drug Carriers / Q000138:chemical synthesis*; D004339:Drug Compounding / Q000379:methods*; D004355:Drug Stability; D004655:Emulsions / Q000008:administration & dosage; D005260:Female; D008055:Lipids / Q000008:administration & dosage; D051379:Mice; D008812:Mice, Hairless; D010316:Particle Size; D010539:Permeability; D010778:Photochemotherapy / Q000379:methods*; D012869:Skin Absorption; D013696:Temperature; D014280:Triglycerides / Q000008:administration & dosage* / Q000737:chemistry
chemical_list: D004337:Drug Carriers; D004655:Emulsions; D008055:Lipids; D014280:Triglycerides; C009683:witepsol; D000622:Aminolevulinic Acid