Investigations into the stabilization of drugs by sugar glasses: III. The influence of various high-pH buffers.
OBJECTIVE
To study the effect of the high-pH buffers ammediol, borax, CHES, TRIS, and Tricine on the glass transition temperature of the freeze concentrated fraction (Tg') of trehalose/buffer and inulin/buffer solutions at pH 6.0 and pH 9.8. Also, the glass transition temperature (Tg) of sugar glasses obtained after freeze drying of these solutions was elucidated. Additionally, the effect occurring during the freezing process on the pH of the various buffers was investigated. Furthermore, the stability of alkaline phosphatase (AP) incorporated in these sugar glasses prepared from solutions at pH 9.8 was evaluated.


METHODS
The Tg' and Tg were measured using differential scanning calorimetry (DSC), and the change of pH during freezing was estimated by using an indicator solution added to the respective solutions. The enzymatic activity of AP after freeze drying and storage at 60 degrees C was evaluated by an enzymatic activity assay.


RESULTS
It was found that the Tg' and Tg of the samples investigated are strongly influenced by the presence of the buffer. On freezing, only minor changes of the pH were observed. The samples with the lowest Tg and the samples containing buffers that formed complexes with the sugars showed the poorest stability of the AP.


CONCLUSIONS
The stabilizing capacities of sugars that are currently recognized as excellent stabilizers for proteins during drying and storage can be completely lost if certain high-pH buffers such as ammediol, borax, and TRIS are used at high concentrations. Loss of stabilizing capacities can be ascribed to strong depression of the Tg' and Tg or to complex formation.
Department of Pharmaceutical Technology and Biopharmacy, University of Groningen, 9713 AV Groningen, The Netherlands.
Jonas H C
JH
Eriksson
Wouter L J
WL
Hinrichs
Gerhardus J
GJ
de Jong
Govert W
GW
Somsen
Henderik W
HW
Frijlink
D000469:Alkaline Phosphatase / Q000737:chemistry; D000818:Animals; D002021:Buffers; D002152:Calorimetry, Differential Scanning; D002241:Carbohydrates / Q000737:chemistry*; D002417:Cattle; D003460:Crystallization; D004355:Drug Stability; D004795:Enzyme Stability; D005612:Freeze Drying; D006863:Hydrogen-Ion Concentration; D007444:Inulin / Q000737:chemistry; D019999:Pharmaceutical Solutions / Q000737:chemistry; D044367:Phase Transition; D014199:Trehalose / Q000737:chemistry
D002021:Buffers; D002241:Carbohydrates; D019999:Pharmaceutical Solutions; D007444:Inulin; D014199:Trehalose; D000469:Alkaline Phosphatase