DESC:Title
Lyophilized preparation of a benzimidazole compound by an improved lyophilization cycle

Background of the invention
Benzimidazole derivatives like omeprazole, pantoprazole, rabeprazole and lansoprazole belong to a class of antisecretory compounds called proton pump inhibitors that do not exhibit anti-cholinergic or histamine H2receptor antagonist properties. Drugs of this class suppress gastric acid secretion by inhibiting the gastric H+ K+ ATPase enzyme system (proton pump) at the secretory surface of the gastric parietal cell. These class of drugs are commonly useful in the prevention and treatment of gastric related diseases, including reflux oesophagitis, gastritis, duodenitis, gastric ulcer and duodenal ulcer. The pharmaceutical compositions of these benzimidazole drugs utilize one or the other means to prevent drug degradation during its shelf life because the benzimidazoles in general, are acid labile drugs and have poor stability in aqueous solution.

Pantoprazole,5-difluoromethoxy-2[(3,4-dimethoxy-2-pyridinyl)methylsulfinyl]-lH- benzimidazole, is a benzimidazole compound that inhibits gastric acid secretion. Pantoprazole is a chiral compound, and the term pantoprazole also includes the pure enantiomers of pantoprazole and their mixtures in any mixing ratio. Pantoprazole also refers to all solvates, and in particular to hydrates, of 5-difluoromethoxy-2[(3,4-dimethoxy-2-pyridinyl)methylsulfinyl]-lH-benzimidazole and salts thereof, preferably pantoprazole sodium sesquihydrate.

Pantoprazole sodium has been approved by the FDA for parenteral administration under the name Protonix IV* and for oral administration under the name Protonix® for short-term treatment of erosive esophagitis associated with gastroesophageal reflux disease (GEHD), for maintenance of healing of erosive esophagitis and for treatment of pathological hypersecretory conditions, including, for example, Zollinger-Ellison syndrome.Particularly, intravenous pantoprazole is indicated for the treatment of patients who require PPI therapy but who are unable to take oral medication.

WO 2009001163 discloses lyophilized pantoprazole sodium containing sodium citrate to overcome drawback of edetate disodium based degradation of pantoprazole.

Patent No DE 432-4014 describes a process for the production of a lyophilized form of pantoprazole sodium sesquihydrate. The said preparation contains, aqueous solutions of pantoprazole sodium sesquihydrate lyophilized in the presence of sucrose, as aid, at a temperature of -25° C to -30° C.

Pantoprazole sodium for injection(Akorn Inc)is the only alternative injectable proton-pump inhibitor(PPI) currently on the US market wherein said product preparation requires a greater than 40 hrs lyophilization cycle.

The future annual US market demand for injectable pantoprazole sodium could increase from the current level of USD 1 billion. Consequently, approaches to “stretch” supplies of injectable pantoprazole are likely to be required. Additionally, various strategies to make injectable pantoprazole available at more affordable prices need to be evaluated.

A typical freeze-drying cycle is comprised of three distinct stages: freezing, primary drying and secondary drying. Development of a successful lyophilized product requires understanding of all three stages, the stresses associated with each and how to resolve the commonly encountered issues.
Tc (Collapse temperature) is the temperature at which the material softens to the point of not being able to support its own structure and Tg’(Glass transition)is the temperature at which frozen material changes from a brittle to flexible structure.Particularly,optimization of primary drying is considered a challenging task, with a significant economic impact, despite knowing the Tc and Tg’ of a given pharmaceutical formulation.

Although not a direct factor for a formulation, the economics of a freeze-drying process may override all other quality factors.The cost of freeze-drying cycles is often dictated by how well optimization was performed to allow scale up. Labor provides additional expense when a cycle is unable to complete on a convenient daily cycle resulting in driers being active but not productive. Any process that can be adapted to reduce these running times or minimize staff will benefit the associated costs.Refer Edmond Ekenlebie et al American Pharmaceutical Review 2011.

Inorder to meet increasing market demand for injectable pantoprazole at an affordable price ,alternative lower cost and efficient lyophilization processes have become highly desirable.

Summary of Invention

An improved and cost-effective lyophilization process for preparation of lyophilized pantoprazole comprising of sublimation below formulation collapse temperature of -110C and secondary drying at 300C for 4 hrs with chamber pressure 25µbar thereby significantly reducing the lyophilization cycle time from 40hrs to 17hrs and providing lyophilized pantoprazole with miniumum residual moisture content.

Brief description of the drawings
Figure 1: Heating DTA and impedance curves for Pantoprazole Sodium Sesquihydrate with edetate disodium by using Lyotherm2.

Figure 2(a): Lyostat2 image at -11.10C for Pantoprazole Sodium Sesquihydrate with edetate disodium.

Figure 2(b):Lyostat2 image at -10.50C for Pantoprazole Sodium Sesquihydrate with edetate disodium.

Figure 2(c):Lyostat2 image at -10.00C for Pantoprazole Sodium Sesquihydrate with edetate disodium.

Detailed description of the Invention
Present disclosure provides lyophilized pantoprazole sodium sesquihydrate prepared by a lyophilization cycle having a total duration between 16 to 18 hours,comprising of following steps:
i) loading the filled vials with precooled shelf at 5?C,
ii) freezing upto -25?C with freezing rate between 5 to 10?C/minute,
iii) obtaining final freezing temperature of -25?C,
iv) holding the frozen mass between -20 to -30?C for 2.5 hrs,
v) stepwise primary drying by increasing the temperature from -25 to -12?C in 30 min, holding for 60 min, at pressure of 125 ?bar; increasing the temperature from -12 to -5?C in 30 min, holding for 3 hrs, at pressure of 125 ?bar; increasing the temperature from -5 to 0?C in 30 min, holding for 3 hrs, at pressure of 75 ?bar,
vi) heating ramp for secondary drying involving change in temperature from 0 to 30?C, achieved in 1 hrs, at a pressure of 50 ?bar,
vii) secondary drying at a temperature between 20 to 30?C, for 4 hrs, at a pressure of 25?bar and
viii) backfiling of vials with nitrogen at pressure of 800?bar

An important aspect of the instant invention is that lyophilization cycle duration for preparation of pantoprazole can be significantly reduced by carrying out sublimation below formulation collapse temperature of -110C.
Yet another important aspect of instant invention is that bound moisture can be removed by carrying out secondary drying at 300C for 4 hrs with chamber pressure of 25µbar.

In some embodiments, the invention provides LyoTherm2 and LyoStat2 (Biopharma Technology Ltd., UK) based methods for measuring energy level changes in Pantoprazole Sodium Sesquihydrate (with Edetate Disodium and adjusted pH) by using Lyotherm2 and Lyostat2 (freeze drying microscopy) during lyophilization cycle development.Paricularly Lyotherm2 can be used to measure a function of electrical impedance (Zsinf) when sample in frozen state, which can indicate changes in ionic/molecular mobility whereas Lyostat2, a Freeze-Drying Microscope System can enable quick and accurate identification of key parameters such as collapse and eutectic temperatures. These critical parameters can be considered for both product lyophilization cycle development.

Further said improved lyophilization cycle having total duration between 16 to 18 hours can provide about 2 fold reduction in manufacturing associated cost as compared to previously reported lyophilization cycle having total duration of 40 hours.

The lyophilized product obtained by improved lyophilization process as described herein i)can have residual moisture content less than 2%,particularly between 0.5 to 1.5% ,ii)can show a Reconstitution time between 15 to 20 seconds and iii)can be stable for 9months when stored at 25°C ± 2°C, 60% ± 5%RH.

Lyophilization may be performed in a container, such as a tube, a bag, a bottle, a tray, a vial (e.g., a glass vial) or any other suitable containers. The containers may be disposable. Controlled freeze and/or thaw may also be performed in a large scale or small scale.

Inventive methods in accordance with the present invention can be used to assess lyophilization cycles developed for various lyophilizers, such as, commercial-scale lyophilizers, pilot-scale lyophilizers, or laboratory-scale lyophilizers.

The pantoprazole solution used in the freeze drying process can be obtained by addition of ethylenediamine tetraacetic acid and/or a suitable salt thereof, and sodium hydroxide and/or sodium carbonate to an aqueous solvent. Suitable salts of ethylenediamine tetraacetic acid which may be mentioned in connection with the invention by way of example are ethylenediamine tetraacetic acid disodium salt, ethylenediamine tetraacetic acid calcium disodium salt ethylenediamine tetraacetic acid trisodium salt and ethylenediamine tetraacetic acid tetrasodium salt.

In a further preferred embodiment of the invention the pH of the solution used in the freeze drying process can be between 9.5 to 10 ,preferably between 9.6 to 9.7.

The lyophilized products in particular contain between 5 and 150 mg, preferably between 5 and 60 mg, of pantoprazole. Examples which may be mentioned are lyophilized products or injections which contain 10, 20, 40, 50 or 96 mg of pantoprazole.

The lyophilized formulation can comprise of pantoprazole sodium sesquihydrate at a concentration of 40mg/vial, ethylenediamine tetraacetic acid disodium salt at a concentration of 1mg/vial , water and can have pH between 9.6 to 9.7.

The production of the lyophilized product by using an improved and cost-effective lyophilization process is described by way of example below. The following examples illustrate the invention in greater detail.

Examples:

Example 1

Evaluation of thermal properties of Pantoprazole by Lyotherm2 & Lyostat2

Initially it was believed that Tg’ and Tc occur at the same
temperatures,however we found that this is not always the case and can be missed even with sensitive methods. Accordingly Lyotherm2 was employed to measure Zsinf — a function of electrical impedance (Martin et al 2007) and differential thermal analysis (DTA) which enabled mobility increases to be identified below traditional critical temperatures.

Lyotherm2 study:
The heating DTA and impedance curves for Pantoprazole Sodium Sesquihydrate with edetate disodium were studied .Refer Figure 1.Pantoprazole Sodium formulation did not show any significant energy changes when heated from -60 ºC till -15ºC. At –110C, the curve showed onset of sharp endotherm suggesting melting of ice and softening of the frozen material thereby signifying occurrence of event just before collapse of the drying mass.

Lyostat2 study:
The Images of Lyostat2 for Pantoprazole Sodium Sesquihydrate with edetate disodium revealed that collapse temperature of the formulation was –10.50C .Refer Figure 2.

Interpretation of Lyotherm 2 & Lyostat 2:
Sublimation below formulation collapse temperature of -110C was found to be the most critical aspect responsible for significant reduction in lyophilization cycle time.

Example 2

Formulation Specifications

Pantoprazole Sodium for Injection (40 mg / vial).

Each vial contains:

Pantoprazole sodium sesquihydrate equivalent to Pantoprazole USP/BP/Ph EUR ----- 40 mg

Edetate Disodium, (Dihydrate) USP-------1 mg

Sodium Hydroxide IP/BP/US, to adjust pH ---------q.s.

Water for Injection USP ---q.s

N2 Gas, USP/NF ---- q.s.

Container Specifications

VialsGlass container 10ml/N20/H57 Clear, Ammonium Sulphate treated tubular USP I,

Elastomeric Closure
Elastomeric Closure GBRFS w/o stelmi C1419

Example 3

Table 1: Low duration (17 hrs)lyophilization cycle
Precooling
Shelf Precooling Yes 5ºC ---
Freezing
Shelf Temp Control Final T ºC Ramp Duration (Min) Soak Duration (Min)
Ramp 1 & soak 1 -25 1 150
Sublimation
Shelf Temp Control Final T ºC Ramp Duration
(Min) Soak Duration (Min)
Ramp 1 & Soak 1 -12 30 60
Ramp 2 & Soak 2 -5 30 180
Ramp 3 & Soak 3 0 30 180
Ramp 4& Soak 4 30 60 1
Chamber pressure control
125 µbar for 300 min, 75 µbar for 210 min, 50µbar for 61 min.
Secondary Drying
Shelf Temp Control Final T ºC Ramp Duration (Min) Soak Duration
(Min)
Ramp 1 and soak 1 30 1 240
Ramp 2 and soak 2 5 20 1
Chamber pressure control 25 µbar for 241 min, 800 µbar for 21 min.

Results:
Lyophilization cycle time was found to be significantly reduced from traditional 40 hrs to 17hrs when sublimation step that was carried below formulation collapse temperature of -110C and a secondary drying in step (g)was carried at a temperature of 30?C, for 4 hrs, at a pressure of 25 ?bar.

Lyophilized pantoprazole prepared by above cost-effective lyophilization process was showing a residual mositure content of 0.5% and reconstitution time for the same was found to be between 17 to 20 seconds.

Example 4 Stability study of lyophilisate

Table 2:Stability profile of Pantoprazole sodium at 25 °C ± 2°C, 60% ± 5%RH
Test Initial 3M 6M 9M 12M
Identification By HPLC Complies Complies Complies Complies Complies
pH 9.7 9.6 9.7 9.7 9.8
Water content 0.8 1.2 1.6 1.4 1.3
Completeness and Clarity of Solution Complies Complies Complies Complies Complies
Particulate matter (Visual) Complies Complies Complies Complies Complies
(Sub-visible) Particle of size = 10µm: 890 726 1178 647 1130
(Sub-visible)
Particle of size = 25µm: 12 44 24 15 10
Colour of Solution 23 APHA 41 APHA 29 APHA 24 APHA 21 APHA
Reconstituted time(seconds:S) 16 S 16 S 17 S 17 S 17 S
Assay (By HPLC) 103.2 102.9 102.7 101.4 102.1
EDTA Assay (By HPLC) 99.4 96.3 103.5 101.9 101.4

Table 3: Test Specifications/Limits
Test Limits
Identification By HPLC The Retention time of the major peak in the chromatogram of the Assay preparation should correspond to that in the chromatogram of standard preparation, as obtained in the Assay.
pH Between 9.0 and 10.5.
Water content Not more than 4.0%.
Completeness and Clarity of Solution Should comply the test.
Particulate matter (Visual) The constituted solution is essentially free from the particles of foreign matter.
(Sub-visible) Particle of size = 10µm: Not more than 6000 per container.
(Sub-visible)
Particle of size = 25µm: Not more than 600 per container.
Colour of Solution Not more than 150 APHA units.
Reconstituted time(seconds:S) Not more than 40 S.
Assay (By HPLC) 90.0% to 110.0% of label claim.
EDTA Assay (By HPLC) 90.0% to 110.0% of label claim.

Determination of particulate matter (sub-visible) was carried as per USP<788> SVP.

The results reveal that the product obtained as above is stable for atleast 12 months when stored at 25 °C ± 2°C, 60% ± 5%RH

Thus, it is apparent that there has been provided, in accordance with the instant invention, a process that fully satisfies the objects and advantages set forth herein above. While the invention has been described with respect to various specific examples and embodiments thereof, it is understood that the invention is not limited thereto and many alternatives, modifications and variations will be apparent to those skilled in the art in light of the forgoing description. Accordingly, it is intended to embrace all such alternatives, modifications and variations as fall with in the spirit and broad scope of invention. ,CLAIMS:We claim:
1. A lyophilized 5- difluoromethoxy- 2- [(3, 4- dimethoxy- 2- pyridinyl) methylsulfinyl]- lH - benzimidazole (pantoprazole) composition prepared by using an improved and cost-effective lyophilization process that comprises of a sublimation step carried below formulation collapse temperature of -110C resulting in a significant reduction in lyophilization cycle time.

2. A lyophilized pantoprazole composition according to claim 1, wherein the composition is prepared by a lyophilization cycle having total cycle time between 16 to 18 hours.

3. A lyophilized pantoprazole composition according to claim 1, wherein said lyophilization process comprises of :
a)loading the filled vials with precooled shelf at 5?C,
b)freezing upto -25?C with freezing rate between 5 to 10?C/minute,
c)obtaining final freezing temperature of -25?C,
d)holding the frozen mass between -20 to -30?C for 2.5 hrs,
e)stepwise primary drying by increasing the temperature from -25 to -12?C in 30 min, holding for 60 min, at pressure of 125 ?bar; increasing the temperature from -12 to -5?C in 30 min, holding for 3 hrs, at pressure of 125 ?bar; increasing the temperature from -5 to 0?C in 30 min, holding for 3 hrs, at pressure of 75 ?bar,
f)heating ramp for secondary drying involving change in temperature from 0 to 30?C, achieved in 1 hrs, at a pressure of 50 ?bar,
g)secondary drying at a temperature between 20 to 30?C, for 4 to 6 hrs, at a pressure between 20?bar to 30?bar and
h)backfiling of vials with nitrogen at pressure of 800?bar.

4.A lyophilization process of claim 3, wherein secondary drying in step (g) is carried at a temperature of 30?C, for 4 hrs, at a pressure of 25 ?bar.

5.A lyophilized pantoprazole composition obtained by lyophilization process of claim 3, wherein reconstitution results in rapid and complete dissolution of a lyophilized mass in less than 20 seconds.

6. A lyophilized pantoprazole composition obtained by lyophilization process of claim 3 having residual moisture content less than 2%.
7. A lyophilized pantoprazole composition according to claim 1, wherein the pantoprazole is present in the form of its salt with a base.
8. A lyophilized pantoprazole composition according to claim 7, wherein the pantoprazole is present as a salt selected from the group comprising sodium, potassium, magnesium and calcium.
9. A lyophilized pantoprazole composition according to claim 8, wherein pantoprazole is pantoprazole sodium.
10. A formulation for lyophilization according to claim 1 comprising of pantoprazole sodium sesquihydrate at a concentration of about 40mg/vial, ethylenediamine tetraacetic acid disodium salt at a concentration of about 1mg/vial , water and having pH between 9.6 to 9.7.