INNOVATORS 2010Incorporation of water-soluble API in lipid-based

microspheres obtained by prilling: from the process to the controlled release mechanisms

Lipid Based Drug Delivery Graduate Student Award

Perrine Pivette1, Vincent Faivre1, Georges Daste2, Michel Ollivon1, and Sylviane Lesieur1

1 Université Paris-Sud XI, UMR CNRS 8612, 5 rue J.B. Clément, 92290 Châtenay Malabry, France ; 2 Sanofi-Aventis, 20 avenue Raymond Aron, 92165 Antony, France

ABSTRACT

• Purpose: The aim of this work is to prepare and characterize lipid microspheres loaded with water-soluble API of industrial interest in order to control its release kinetics. The purpose here focuses on the correlation between the process and the release properties.

• Methods: Sustained release microspheres for oral route were obtained by melting excipients and API. By extrusion through vibrating nozzles, molten solutions were dispersed into calibrated droplets which solidify during their fall in a temperature-regulated air column. Microspheres were essentially characterized using XRD, DSC and SEM.

• Results: Model equations were established to predict the solidification time required to crystallize the molten mixture as a function of its thermal characteristics and optimize prilling operating parameters. It results from these calculations that droplet cooling rates are very fast, in the range of thousands of K/min.

Taking advantage of the process and this rapid cooling rate, it is possible to generate perfectly spherical microspheres in which the crystalline domains are very thin and drug finely dispersed. In such kind of inert lipid-based microspheres, and considering the important water-solubility of the API, the release kinetics is governed i) by the water diffusion through the drug-filled channels and ii) by the API molecular diffusion in the pores created after drug dissolution.

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ABSTRACT

• In practice, microspheres were prepared, characterized and dissolution analysis attested a prolonged release dissolution profile. Shape studies have shown that the matrix remains globally intact during dissolution.

• To get further insight onto the drug release mechanisms, XRD and HPLC analysis were made simultaneously to quantify the solubilized-drug fraction within the particles and the effective released fraction respectively. The XRD analysis also confirmed the stability of the lipid matrix structure at a supramolecular level, allowing the use of model equations based on dissolution-diffusion mechanisms to fit the kinetics data.

• Conclusion: In agreement with the theoretical prediction, we prepared by prilling process lipid microspheres able to control the release of a water-soluble drug. Monitoring the crystallized-API disappearance within the matrix complements classical dissolution methods which measure the drug fraction released in the dissolution media.

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INTRODUCTION

• Microspheres, as a delivery system for oral route, present some interest compared to monolithic delivery system:

• Easier administration

• Distribution over a large area : better reproducibility of the stomach filling lower risk of physical injury of the gastro-intestinal tract.

• Lipid formulation• Enhancement of hydrophobic drug bioavailability

• Control release rate

• Taste masking

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INTRODUCTION• Prilling

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Heater

Prilling head

Coo

ling

tow

er

Liquid phase

Solid phase

Heating

Extrusion of the liquid through calibrated nozzles and break up of the liquid jet with a vibrating technology

Solidification of the liquid droplets during falling in cool air (10-20°C)

Microspheres 300-400 µm

Prilling has the advantage to produce solid microparticles, very reproducible in size and shape but implies very fast cooling rates which could lead to supercooling phenomenon or crystallization into unstable forms, due to polymorphic behaviour of the materials.

INTRODUCTION

• It is well known that lipid components exhibit complex physical state behaviour depending on thermal treatments and/or the temperature of storage, mainly due to their polymorphic properties.

• Therefore, the knowledge of thermotropic and structural characteristics of the lipids appears a necessary prerequisite for our research work to control lipid-based formulation and its stability with time as a function of the preparation process.

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OBJECTIVES

• To evaluate theoretically and experimentally the solidification behavior of two lipid excipients: Compritol® and paraffin, during the production of microspheres through prilling process [1].

• To characterize prilled microspheres loaded with an highly water-soluble drug.

• To better understand dissolution kinetics using X-Ray based

methods.

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MATERIALS

• Compritol® (glyceryl behenate): mixture of mono-, di-, tri- glyceride of behenic acid→ melting point 69-74°C

• Paraffin wax: aliphatic chains (mean C27)

→ melting point 52-54°C

We studied the solid state of both binders separately and in a 50/50 (w/w) binary mixture.

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METHODS– The thermal behaviour of Compritol and paraffin (transition temperatures and

enthalpy variation) were studied by differential scanning calorimetry (DSC): DSC 7 Perkin-Elmer, heating/cooling from 10 to 90°C at 5°C/min.

– Structural characterization was performed by Small and Wide Angle X-ray Diffraction (SAXS-WAXS XRD) measurements: SAXS beamline of the Elettra synchrotron (Trieste, Italy) and Lab instrument (UMR 8612).

– Microcalix, a device developed in our laboratory which coupled X-ray diffraction and calorimetric study was also used [2]. Thanks to this device, we finely correlated thermal and structural behaviours of the lipid binders.

– SEM (Scanning Electron Microscopy)

– X-Ray Microtomography Elettra synchrotron (Trieste, Italy)

– Complementary studies: HPLC, infrared, polarized light microscopy, particle size analysis

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RESULTS• A first part of our work was to established model equations to predict the

solidification time required to actually crystallize the lipid as a function of its thermal characteristics and then optimize operating temperatures within the prilling tower. Indeed, the main issue of prilling process is to obtain solid microspheres at the end of the process.

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Crystallization time tc+Time to reach crystallization temperature tr

Time to obtain solid microspheres =

ai

acdpmr TT

TT

h

dCt ln

6

Volumic mass of molten lipid (kg/ m3)

Heat transfercoeffi cient (W/ m2K)

Specifi c heat capacity (kJ / kg.K)

Dropletdiameter (m)

)( ac

cmc TTh

LHt

Latent heat of crystallization (kJ / kg)

Characteristic length (m)

Tc Crystallization T°CTa Air cooling T°CT i I nitial heating T°C

RESULTS

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Time necessary to obtain solid microspheres compared to the fall duration of the particles in the device shows that solid microspheres can be yielded in the experimental conditions used even if paraffin alone behaves closely to the limits of the process.

Numerical application (heating T° 95°C, air T° 10°C)

tr tcTotal solidification

time

CP 0.2s 0.7s 0.9CP + PF 0.5s 0.4s 0.9sPF 0.5s 1s 1.5s

Fall time available in prilling tower 1.5 - 1.6s

9080706050403020

Temperature (°C)

ΔHmelt/crys129 J/g

DSC 5°C/min

Tonset 54°C

Tonset 72°C

Compritol

Paraffin

Compritol + Paraffin50/50 w/w

Tonset 67°C

ΔHmelt/crys138 J/g

ΔHmelt/crys107 J/g

Hea

tfl

ow (

endo

up)

Thanks to data provide by DSC and data provide in the literature, we were able to calculate solidification time for Compritol, Paraffin and a 50/50 (w/w) binary mixture of both.

RESULTS• Morphological study by SEM:

In practice, microspheres were produced with the setting temperatures presented before and a morphological study by SEM was performed to evaluate the proper conduct of the process.

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No traces of impaction are visible on the microgranule surfaces, confirming their solidification before final contact with the prilling device walls.

X 7

.

0.240.200.160.120.080.04 0.400.30 1.701.601.501.400.240.200.160.120.080.04 0.400.30 1.501.40

X 7

.

0.240.200.160.120.080.04 0.400.30 1.701.601.501.400.240.200.160.120.080.04 0.400.30 1.501.40

bulkspheres

SAXS WAXS

Compritol

Compritol+ Paraffin

Paraffin

q Å-1

61.6Å

37.3Å

62.3Å37.7Å

62.4Å

37.3Å

63.2Å 37.9Å

Orth.

Orth.

Sub-α

Sub-αIn

tens

ity

(a.u

.)

RESULTS• Then, we studied the incidence of the fast cooling rate on the structure.

To do so, we compared the XRD pattern of bulk samples, slowly cooled at 5°C/min, with XRD pattern of microspheres obtained by prilling.

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X-Ray diffraction Bragg reflections occur almost at the same positions in either bulk matrix or microspheres. However, the diffraction peaks from microspheres appear broader and less intense.The very fast cooling added to the dispersed liquid state likely disturbs crystal growth within droplets so that long-range packing of molecules is less ordered.

RESULTS• Drug loaded microspheres: highly water-soluble drug +

binary mixture of Compritol/Paraffin– Dissolution tests were performed according to the pharmacopeia

standards by measuring released fraction in the dissolution media with time.

– To go further into the understanding of the release mechanism, we also checked the structural state of microspheres during the dissolution test by analyzing microspheres with XRD at each control point.

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XRD (microspheres)Remaining crystalline drug and lipid structure characterization

HPLC (dissolution medium) Drug release measurement

RESULTS• The dissolution profile shows a sustained release of the drug.

• XRD during dissolution media incubation: intensity and surface area decrease of drug diffraction peaks with time informs about drug solubilization.

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Solubilized fraction Solubilized fraction

0

0.2

0.4

0.6

0.8

1

0 50 100 150 200

Time (min.)

Sol

ubi

lized

or r

elea

sed

frac

tion

Released fraction

inte

nsi

ty(a

.u.)

0.500.400.300.20

q (A-1)

1.81.61.41.21.0

t 0

t + 8h

Lipid matrixAPI

inte

nsi

ty(a

.u.)

0.500.400.300.20

q (A-1)

1.81.61.41.21.0

t 0

t + 8h

Lipid matrixAPI

X-Ray Diffraction

The structural (XRD) and morphological (SEM) stability of the lipid matrix during dissolution confirms a mechanism of diffusion from a non degradable system (no erosion or swelling).

SEM Before dissolution

After dissolution t+24h

RESULTS

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A time 0, we observe completely filled microspheres while we observe a corona of channels on partially loaded particles.

• X-Ray Microtomography: To confirm diffusion mechanism, we compared totally loaded and partially emptied microspheres.

Virtual slices

Drug loaded microspheres Partially emptied microspheres

Drug releaseCrystalline

drug

Water diffusion

Resolution 3.4 µm

Corona Corona thicknessthickness

In these inert lipid-based microspheres, loaded with water-soluble drug finely dispersed, release kinetics is governed by: i) diffusion of the dissolution medium through the drug-filled pathways, ii) solubilized drug diffusion through micronic liquid filled channels created by its progressive dissolution.

CONCLUSION

• The studied lipid excipients, Compritol® and paraffin, were shown suitable for production of crystalline microspheres by prilling, in agreement with the theoretical prediction.

• The fast cooling kinetics imposed by prilling induces slightly disordered organization but does not lead to polymorphism troubles.

• It is possible to load this lipid microspheres with a water-soluble drug.

• Monitoring API solubilisation within the crystalline matrix complements classical dissolution methods measuring the drug fraction released in the dissolution media.

• Drug release is governed by both water diffusion into microspheres and drug diffusion through the channels created by its solubilization.

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ACKNOWLEDGMENTS

• UMR 8612 CNRS: V. Faivre, S. Lesieur, M.Ollivon;

And all the team «physico-chimie des systèmes polyphasés».

• Sanofi-Aventis: G. Daste and all the «prilling» team.

• MEB: N. Tsapis, CECM Vitry sur Seine, France.

• X-Ray Diffraction: H. Amenitsch, ELETTRA synchrotron, Trieste, Italy.

• X-Ray Microtomography: L. Mancini, ELETTRA synchrotron, Trieste,

Italy.

• Dissolution: C. Guetin, (HPLC), A. Chaar (Master 1)

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REFERENCES

• [1] P. Pivette, V. Faivre, G. Daste, M. Ollivon, S. Lesieur; Rapid cooling of lipid in a prilling tower Theoretical considerations and consequences on the structure of the microspheres, J. Therm. Anal. Cal.. (2009), 98:47-55.

• [2] M. Ollivon, G. Keller, C. Bourgaux, D. Kalnin, P. Villeneuve, P. Lesieur; DSC and high resolution X-ray diffraction coupling, J. Therm. Anal. Cal. (2006), 85: 219–224.

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BIOS/CONTACT INFOPerrine PIVETTE is a PhD student in Physical-Chemistry and Pharmaceutical Technology from University Paris-Sud 11 (France), Laboratory UMR CNRS 8612 (Physical-chemistry, Pharmaceutical technology, Biopharmaceutics).

She received her PharmD. degree in 2006 from University of Angers (France). In the same year she received her Master’s degree in Pharmaceutical Technology and Biopharmaceutics (Conception and development of dispersed systems and solid formulations) from University Paris-Sud 11 (France).

She joined the UMR CNRS 8612 (Paris University) for her PhD program under supervision of Dr Vincent FAIVRE, Dr Sylviane LESIEUR, Dr Michel OLLIVON in a collaboration with Sanofi-Aventis company. Her doctoral research is focused on the study of constituents and process parameters influence on the drug release kinetics from lipid microspheres obtained by a prilling process.

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Address: UMR CNRS 8612, Universite Paris-Sud 11; 92296 Chatenay Malabry; FrancePhone: +33630207663Mail: perrine.pivette@u-psud.fr (University) / perrine.pivette@free.fr (Personal)