Thermal characteristics of poly (DL-lactic acid) microspheres containing neurotensin analogue.
The thermal characteristics of poly (DL-lactic acid) (DL-PLA) microspheres containing a hexapeptide (NA: H(CH3)-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 (Tg) of the polymer was observed in DL-PLA microspheres containing NA. The Tg of DL-PLA (PLA2000 bulk) was 307.8 K, while Tg of microspheres containing NA (content 6.0%) shifted to 321.2 K. The Tg 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 degrees C and 40 degrees C 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 degrees C for 1 month. This may be attributed mainly to a decrease in surface area caused by the formation of agglomerates of PLA2000 microspheres under conditions near Tg.
Yamakawa
I
I
Tsukuba Research Laboratories, Eisai Co., Ltd., Ibaraki, Japan.
Ashizawa
K
K
Tsuda
T
T
Watanabe
S
S
Hayashi
M
M
Awazu
S
S
D004356:Drug Storage; D007773:Lactates / Q000737:chemistry*; D019344:Lactic Acid; D008863:Microspheres; D009496:Neurotensin / Q000031:analogs & derivatives* / Q000737:chemistry*; D011091:Polyesters; D011108:Polymers / Q000737:chemistry*; D013696:Temperature
D007773:Lactates; D011091:Polyesters; D011108:Polymers; D019344:Lactic Acid; D009496:Neurotensin; C033616:poly(lactide)