This document summarizes research on the anomalous behavior of mannitol during freeze drying. Mannitol exists in three polymorphic forms (α, β, δ) that have different solubilities and stabilities. The β form has low solubility and is crystalline in nature. Rapid transformation to the stable β form during freeze drying can result in a hazy or turbid solution. Process variables like freezing and annealing rates can affect the resulting polymorph. Approaches to prevent this issue include using a solvent mixture to promote the amorphous δ form, or combining mannitol with other excipients like trehalose that improve stability. Analytical tools like XRD and SEM were used to characterize the polymorphic forms.

1. YICC-2011 Solution
Anomalous behavior of Mannitol
Presented by-
Parth Shah,
YICC-2011,
ICT, Mumbai

2. INTRODUCTION
 MANNITOL : mainly used as bulking agent
and cryoprotectant.
 CRITERIA FOR USING BULKING AGENT: API<2%
 ADVANTAGE : When formulation frozen slowly produce
crystals which supports API and prevent loss of product
 USUALLY NON-REACTIVE WITH ACTIVE
CONSTITUENT
 Provides more stable cake of API as compared to lactose
 DISADVANTAGE: Mannitol interacts with proteins and
forms turbid and hazy solution on storage

3.  Selection of excipient depends on interaction with API .
 Mannitol is a hexahydric alcohol that has been
extensively used as an excipient for the freeze drying of
pharmaceuticals
 Mannitol differs from other cryo- or lyo-protectant in
that it tends to recrystallize on drying, supposedly via
eutectic formation with water in contrast to the behavior
of materials such as sucrose and trehalose that form
amorphous products after completion of the drying
process.

4. STRUCTURAL BEHAVIOUR
 Mannitol is believed to exist in three forms designated as
α, β, and δ
 δ polymorph has loose carbon
backbone but strong H-bond
 β polymorph has strong
C-backbone but weak H-bond
 Polar -OH group of water
breaks strong H-bonding of δ
polymorph and leads to
convert to stable β form.

5. MANNITOL
 Polymorph formation depends on protocol and conc. Of
mannitol used.
 Parameters:
 Ice crystal nucleation temp. and cooling rate
 Nucleation at higher temp gives stable compound Tn:
-2.6oC gives 60%wt stable β product
 Nucleation at lower temp. less stable compound Tn:
-7.8oC gives only 2% stable product
 Cooling rate plays crucial role
 Fast rate: low stability (-2oC/min)
 Slow rate: High stability(-0.5oC/min)

6. COOLING RATE EFFECT ON DISTRIBUTION

7. PROCESS VARIABLES
 Effect of conc. Variation: 1.5%, 3%w/w yields β form where
as higher conc. Like 7.5%,10% yields mix α,β form.This 10%
system after fast cooling gives δ form.
 Effect of Annealing temp.:annealing step i.e slow rate of
cooling temp. is essential for 100% crystalinity
 With increase in conc. From 1.5,3,5,7,10% w/v amount of
crystaline product increase
 Annamolus behaviour of mannitol: Unlike all other sugars in
thermodynamic graph of mannitol 3% solution through DSC
plot cooling from 10 o showed exotherm at -21o followed by
smaller isotherm at -29o.But degree of reproducibilty was -24o

8. Anomalous behavior of Mannitol

9. Effect of cooling Rate

10. Why could this problem have occurred?
 This problem could be due to formation of β
polymorph which has low solubility due to its
crystalline nature
 This problem may even divert to interaction between
mannitol and API if the anti cancer drug is
protenious in nature
 The other possibility is crystallization of buffer used
such as sodium acetate in our case which crystalise
during freeze drying but form complex which has low
probability of hydration

11. Do you think this problem is due to Mannitol?
 Yes this problem is mainly concentrated to dynamic
polymorphic nature of Mannitol
 Rapid transformation from meta stable α, δ
polymorphic form to stable β form which is
crystalline in nature and driven by moisture

12. X-ray diffraction patterns of mannitol samples; (a)
recrstalized sample, (b) commercial product.

13. Effect of Surface Area on transition
Hygroscopic of δ
polymorph is 2.2 times
greater than β polymorph

14. Lyophilizaion of Mannitol

15. PARAMETERS
 Process variables:
1. Freezing rate
2. Annealing temperature (for Mannitol is -29 o C)
3. Secondary drying temperature
 Product responses:
1. Ice crystalization temperature
2. Onset and duration of mannitol crystalization
3. Cooling rate
4. Duration of primary drying
5. Residual moisture content

16. Approaches for prevention of fibers
 Solvent used for mannitol freeze drying process is
mixture of acetone/ water
 Mannitol is not soluble in acetone and its stability is
6 months
 This approach will help to produce and preserve δ
polymorph which is amorphous in nature and hence
will resolve the fibre problem if it is due to crystaline
nature of β polymorph

17. 2nd Approach
 For the increase in stability of protein drugs using a mixture of
excipient like mannitol/sorbtol and mannitol/trehalose . In the
mannitol/sorbitol co-solute systems the spray dried samples
containing lysozyme and trypsin showed a decrease in
stability with an increase in sorbitol content of the initial sample.
The enzymatic assays revealed that addition of sorbitol to
the initial mixture caused a decrease in retained activity
immediately after production and after storage for four weeks at
75%
 RH and 40°C. Loss of structural integrity was confirmed from
Raman data. Co-spray drying the proteins with
 trehalose/mannitol gave a higher retained activity both before and
after exposure than the mannitol/sorbitol samples.

18. ANNALYTICAL APPROACH
SCANNING ELECTRON MICROSCOPY HELPS TO STUDY MORPHOLOGICAL
NATURE OF CRYSTALS
Scanning electron-micrographs of δ-crystal; (a) before, (b) after exposure to
97%RH for 20 h

19. XPRD
X-ray diffraction patterns of mannitol samples; (a) recrystallised
sample, (b) commercial product.
Referential X-ray diffraction patterns of polymorphic forms of
mannitol; (a) α form (b) β form, (c) δ form

20. CONCLUSION
 FIBER FORMATION CAN BE EITHER
PREVENTED BY FORMING AND PRESEVING
AMORPHOUS STAGE WHICH HAS SOLUBILITY
IN AQUEOUS STATE
 BY FORMING COSOLVENTS SUCH AS
MANNITOL/TREHALOSE IS FOUND TO BE
SUCCESFUL
 BY ARRANGING DESSICANT IN VIAL STOPPER
SO THAT IT MAINTAIN DESIRED MOISTURE
LEVEL SO THAT δ POLYMORH IS PRESEVED

21. REFERENCE
1. International Journal of Pharmaceutics Volume 247, Issues
1-2, 24 October 2002, Pages 69-77.
2. Chemical Engineering Research and Design Volume
87, Issue 8, August 2009, Pages 1017-1027
3. Lyophilization Introduction and basic principles,Thomas
Jenning
4. JOURNAL OF PHARMACEUTICAL SCIENCES, VOL.
92, NO. 9, SEPTEMBER 2003
5. T. Yoshinari1, R. T. Forbes1, M. Mercer2, P. York1
1University of Bradford: Bradford, United Kingdom ; 2Hiden
Analytical Ltd.: Warrington, United Kingdom
6. R. forbes1, W. hulse1, M. bonner1, S. burgess2
7. pharmacy, university of bradford, 2merck speciality
chemicals, merck uk