Thermal Characteristics of Poly (DL-Lactic Acid) Microspheres Containing Neurotensin Analogue

概要

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The thermal characteristics of poly (DL-lactic acid) (DL-PLA) microspheres containing a hexapeptide (NA : H(CH_3(Arg-Lys-Pro-Trp-tert-Leu-Leu-OEt) with neurotensin activity were investigated. PLA microspheres with a drug content of 1.5-11.0% were prepared by a novel o/w (oil-in-water) solvent evaporation method. Both DL-PLA and NA were amorphous in form, and an increase in heat capacity at glass transition temperature (T_g) of the polymer was observed in DL-PLA microspheres containing NA. The T_g of DL-PLA (PLA2000 bulk) was 307.8 K, while T_g of microspheres containing NA (content 6.0%) shifted to 321.2 K. The T_g of PLA2000 microspheres was found to increase with an increase in the content of NA, and its increasing tendency reached a plateau at an NA content of greater than 6%. The apparent activation energy of glass transition of PLA2000 bulk and the microspheres was calculated to be 86.3 and 99.3 kcal/mol, respectively. As a result of the release test after storage at 4℃ and 40℃ for 1 month, nearly the same release profiles of NA from PLA2000 microspheres were found. The release rate of NA after the initial release became slow after storage at 45℃ for 1 month. This may be attributed mainly to a decrease in surface area caused by the formation of agglomerates of PLA 2000 microspheres under conditions near T_g.
公益社団法人日本薬学会の論文
1992-10-25