The Effect of Crystallizing and Non-crystallizing Cosolutes
on Succinate Buffer Crystallization and the Consequent pH Shift
in Frozen Solutions
Received: 23 July 2010 /Accepted: 13 September 2010 /Published online: 7 October 2010
Springer Science+Business Media, LLC 2010
Purpose To effectively inhibit succinate buffer crystallization
and the consequent pH changes in frozen solutions.
Methods Using differential scanning calorimetry (DSC) and X-
raydiffractometry(XRD),thecrystallization behavior of
succinate buffer in the presence of either (i) a crystallizing
(glycine, mannitol, trehalose) or (ii) a non-crystallizing cosolute
(sucrose) was evaluated. Aqueous succinate buffer solutions,
50 or 200 mM, at pH values 4.0 or 6.0 were cooled from
room temperature to −25°C at 0.5°C/min. The pH of the
solution was measured as a function of temperature using a
probe designed to function at low temperatures. The final
lyophiles prepared from these solutions were characterized
using synchrotron radiation.
Results When the succinic acid solution buffered to pH 4.0, in
the absence of a cosolute, was cooled, there was a
pronounced shift in the freeze-concentrate pH. Glycine and
mannitol, which have a tendency to crystallize in frozen
solutions, remained amorphous when the initial pH was 6.0.
Under this condition, they also inhibited buffer crystallization
and prevented pH change. At pH 4.0 (50 mM initial
concentration), glycine and mannitol crystallized and did not
prevent pH change in frozen solutions. While sucrose, a non-
crystallizing cosolute, did not completely prevent buffer
crystallization, the extent of crystallization was reduced.
Sucrose decomposition, based on XRD peaks attributable to
β-D-glucose, was observed in frozen buffer solutions with an
initial pH of 4.0. Trehalose completely inhibited crystallization
of the buffer components when the initial pH was 6.0 but not
at pH 4.0. At the lower pH, the crystallization of both trehalose
dihydrate and buffer components was evident.
Conclusion When retained amorphous, sucrose and treha-
lose effectively inhibited succinate buffer component crystalli-
zation and the consequent pH shift. However, when trehalose
crystallized or sucrose degraded to yield a crystalline decom-
position product, crystallization of buffer was observed.
Similarly, glycine and mannitol, two widely used bulking agents,
inhibited buffer component crystallization only when retained
amorphous. In addition to stabilizing the active pharmaceutical
ingredient, lyoprotectants may prevent solution pH shift by
inhibiting buffer crystallization.
KEY WORDS buffer crystallization
Freeze-dried formulations are, typically, multi-component
systems containing excipients in addition to the active
pharmaceutical ingredient (API) (1–4). For example, a
freeze-dried protein formulation may contain a buffer,
bulking agent, lyoprotectant and surfactant (5). Since a
large fraction of APIs are stable only over a narrow pH
range, buffering the prelyo solution becomes necessary (6).
The selection of a buffer and its concentration are based on
desired pH and buffer capacity as well as the possibility of
buffer-specific catalysis (7,8). When the prelyo solution is
cooled, a potential complication is the pH shift brought
about by the selective crystallization of a buffer component.
R. Suryanarayanan (*)
Department of Pharmaceutics, College of Pharmacy
University of Minnesota
Minneapolis, MN 55455, USA
Scientific affairs, Teva Parenteral Medicines Inc.
Irvine, CA 92618, USA
Pharm Res (2011) 28:374–385