In-Vitro Dissolution Method For Uniform And Sustained Release Of Olanzapine
Field of the Invention
The present invention relates to development of an in-vitro dissolution method for uniform and sustained release of Olanzapine from an in-situ gel forming injectable depot liquid composition. The in-vitro dissolution method is performed according to USP dissolution method II (Paddle method, 75 rpm) employing 0.02N HCI as dissolution media for the first 12hr; followed by changeover to 0.1 N HCI for the next 36hr.
Background of the Invention
Dissolution of drugs from the solid dosage forms is a key parameter in assessing the product quality and uniformity at the formulation stage as well as throughout the shelf-life of the product. The significance of a dissolution test is based on the fact that for a drug to be absorbed and available to the systemic circulation, it should be in the solution form. Therefore, in-vitro dissolution test was introduced not only for quality control to assess batch-to-batch consistency of release from a drug product, but also in an attempt to identify potential problems of in-vivo drug release and absorption.
Olanzapine (2-methyl-4-(4-methyl-1-piperazinyl)-10 H-thieno [2, 3-b][1,5] benzodiazepine) is a psychotropic agent useful in the treatment of schizophrenia, hallucinations, delusions and other bipolar disorders. Olanzapine is poorly water soluble i.e. solubility at pH 6.8=0.02mg/ml. The undissolved product is particularly problematic when dealing with potent compound like Olanzapine. Potential dosing variations can occur if the active is not completely dissolved. For such drugs, difficulties are usually encountered in selecting a dissolution media of acceptable volume and composition as well as of a good discriminating power.
Olanzapine, is commercially available as conventional tablets, orally disintegrating tablets and intramuscular injection formulations, under the tradename Zyprexa® tablets and Zyprexa® Zydis orally disintegrating tablets and Zyprexa® IM injection and Zyprexa® relprevv as long acting IM injection. The official media recommended for the dissolution of Olanzapine tablets as per USFDA is 0.INHCI.
Formulations have been developed which are injected as a liquid, but undergo a change to a solid formulation in-vivo, the so called in-situ gelling systems. This delivery system has unique challenges associated with its in-vitro dissolution method. One of the biggest challenges is to use such a media which provides the desired release profile from the depot without exhibiting burst effect.

PCT application No. 00/18408 assigned to Eli Lilly discloses injectable sustained release oleaginous or cholesterol formulation of Olanzapine or Olanzapine pamoate or solvate thereof, wherein the dissolution was carried out in Dulbecco's phosphate buffered saline pH at 7.4.
Use of the dissolution media as described in the prior art would lead to incomplete dissolution because Olanzapine is poorly soluble in phosphate buffered saline pH 7.4. Therefore, challenge remains to develop and identify a reliable and discriminating method that can characterize the drug release from the formulation. Thus there still remains a need to develop such a dissolution method which can provide a uniform, sustained and complete release of Olanzapine without any initial burst effect and incomplete release. Additionally, the main challenges are to determine the appropriate duration and the times at which samples are to be withdrawn in order to characterize the release profile adequately.
We have worked to develop such an in-vitro dissolution method which ensures uniform and sustained release of Olanzapine from the in-situ gelling system by the use of a unique dissolution media.
Summary of the Invention
According to one embodiment there is provided an in-vitro dissolution method for an in-situ gel forming injectable depot liquid composition of Olanzapine in which the dissolution is performed according to USP dissolution method II (Paddle method, 75 rpm) employing 0.02N HCI as dissolution media for the first 12hr; followed by changeover to 0.1 N HCI for the next 36hr.
According to another embodiment there is provided an in-vitro dissolution method, wherein the sampling is performed from 1hr of placing the composition in the dissolution media upto 48hr at regular intervals.
Detailed Description of the Invention
It has been found that by using the method according to the invention the amount of Olanzapine release from the in-situ gel forming injectable depot liquid composition can be uniform as well as sustained without the aforementioned problems like burst effect and incomplete release.
The term "dissolution media" as used herein, means the liquid media into which the active substance is being released. Examples of dissolution media can be water with or without surfactant, simulated intestinal fluid with or without enzymes, simulated gastric fluid with or

without enzyme, simulated saliva, or the authentic physiological versions of these fluids, aqueous alcoholic solutions (e.g. low molecular weight alcohols miscible in water typically containing 5 or less carbons to act as a cosolvent) and various buffer solutions (e.g. glycine, citrate, acetate, phosphate, and borate buffers).
Suitable dissolution media may be selected from one or more of Hydrochloric acid (HCI), Acetate buffer and Phosphate buffer.
Optionally, the dissolution media can contain a surfactant, which is another way to manipulate the solubility of the system. Typical useful surfactants are selected from non-ionic, cationic, anionic and zwitterionic surfactants. Illustrative examples of surfactants suitable for use in the present invention are sodium dodecyl sulfate, Tween 80, chenodeoxycholic acid, glycocholic acid sodium salt, Tween 20, taurocholic acid and triton X-100.
The ionic strength and pH of the solution are also very critical parameters to be considered. Accordingly, appropriate pH and ionic strength values can be obtained through use of one or more of strong acids, strong bases, and salts, single or multiple conjugate acid-base pairs, monoprotic and polyprotic electrolytes etc.
Representative electrolyte solutions can be, but are not limited to, hydrochloric acid solutions and sodium chloride solutions and mixtures thereof, to simulate the human gastrointestinal tract. Exemplary solutions of salts, acids, bases or combinations thereof, which exhibit the desired pH and ionic strength, include but are not limited to phosphoric acid/phosphate salts + potassium, sodium, calcium salts of chloride, acetic acid/acetate salts+ potassium, sodium and calcium salts of chloride, carbonic acid/bicarbonate salts + sodium, potassium and calcium salts of chloride, and citric acid/citrate salts + sodium, potassium and calcium salts of chloride.
Dissolution apparatus are well known in the analytical art and some have been standardized e.g. in various pharmacopeia such as the United States Pharmacopeia or the Japanese Pharmacopeia. Illustrative examples of dissolution testing apparatus are the rotating basket method (e.g. USP I), the paddle method (e.g. USP II), the reciprocating cylinder apparatus (e.g. USP III), various flow through methods (e.g. USP IV) and various transdermal dissolution testing apparatus (e.g. Franz diffusion cell).
In one preferred embodiment of the invention a paddle assembly is employed as the dissolution testing apparatus with paddles rotating at 65-85 rpm, more preferably at 75 rpm.

Suitable analytical method can be any method known in the art, including but not limited to, Gas Chromatography, Liquid Chromatography, High Performance Liquid Chromatography (HPLC), Colorimetry, UV Spectroscopy, IR Spectroscopy, Raman Spectroscopy, Mass Spectroscopy, Electro Chemical Methods and Nuclear Magnetic Spectroscopy. The preferred one is the HPLC.
The term "dissolution profile" or "release profile" as used herein, refers to the change in concentration with time of the substance being tested.
"Burst effect" often results in a substantial portion of the active agent, if not all, being released in a very short time, e.g. 1-3hr.
The term "uniform and sustained release" as used herein indicates that the therapeutically active medicament (Olanzapine) may be released from the composition at a controlled rate in such a manner that blood levels (that are still below the toxic levels of the medicament) may be maintained at therapeutically beneficial levels over an extended period of time of at least 48hr.
The term "in-situ gel forming injectable depot liquid composition" as used herein refers to the formulation which is injected as a liquid, but undergoes a change to a solid formulation in-vivo.
The term "depot" refers to a substance containing the active that is retained in close proximity to the site of injection so that release of the active agent occurs over a prolonged period of time.
The term "liquid" refers to having a viscosity that will permit displacement of a material without application of pressure. The in-situ gel forming depot liquid composition of Olanzapine, typically exhibit viscosity from about 1 cps to about 500 cps, preferably from about 1 to about 300 cps. More preferably, the viscosity of the in-situ gel forming injectable liquid composition is from 1-100 cps.
The in-situ gel forming injectable depot liquid compositions of Olanzapine and their method of preparation are described in IN2745/DEL/2009 (incorporated herein by reference).
The in-vitro dissolution method as per the present invention involves carrying out the dissolution of the composition for 12hr in 0.02N HCI using dissolution apparatus (USP type II) with paddles rotating at 75 rpm with subsequent withdrawing of the sample at regular intervals and replacing with the fresh media (0.02N HCI). After 12hr, withdrawing the sample and replacing with 0.1 N HCI media and carrying out the dissolution for the next 36hr with subsequent withdrawing of the

sample at regular intervals and replacement with 0.1N HCI. Evaluating the % drug dissolved by using HPLC.
The following non-limiting examples illustrate the various tests performed to develop the optimum dissolution method.
Example 1:
(Table Removed)
*Acid terminated end group
Process for the preparation:
1. Olanzapine was dissolved in N-methyl-2-pyrrolidone to obtain a solution.
2. To the solution obtained in step 1, PLGA 502H was added and it was then sterilized.
3. The sterilized solution of step 2 was filled in a suitable vial or syringe and flushed with nitrogen and sealed.
The dissolution profile of Example 1 in HCI media is provided in Table 1 below.
Table 1:
(Table Removed)
The above results show the effect of varying the pH of the media on the release profile of Olanzapine. The results indicate that as the pH of the dissolution media decreases, release of the drug increases with initial burst release in more acidic media and incomplete release in less acidic media. This is because the solubility of the basic drug like Olanzapine increases as the acidity of the media increases.
The dissolution profile of Example 1 in Acetate buffer media (pH 3.4) is provided in Table 2 below:

Table 2:
(Table Removed)
The obtained results show that the release is non-uniform and more than 65% drug is released in 6hr which is not desirable. Further, problem in the solidification of the composition is observed while using Acetate buffer as dissolution media. These problems make this media unsuitable for carrying out the dissolution of such a composition.
Table 3 below shows the effect of temperature on the release profile of Olanzapine composition prepared in example 1.
Table 3:
(Table Removed)
The results indicate that by increasing the temperature to 40°C from 30-48hr there is a decrease in the release of Olanzapine. This is due to the degradation of the drug in the solution form at higher temperature.
The composition prepared in Example 1 is subjected to such dissolution conditions in which after 24hr, the initial media is replaced with the fresh media. The dissolution profile is provided in the Table 4 below.
Table 4:
(Table Removed)
The results show that release becomes faster when media is replaced with the fresh media after 24hr however there is no significant increase in the release of Olanzapine.

The composition prepared in Example 1 is subjected to such dissolution conditions in which 0.2% NaCI is added to the dissolution media. The dissolution profile is provided in the Table 5 below.
Table 5:
(Table Removed)
The results indicate that release is faster with the addition of the electrolyte solution in the media.
The composition prepared in Example 1 is subjected to such dissolution conditions in which after 12hr, initial media is completely replaced with the second media. The dissolution profile is provided in the Table 6 below.
Table 6:
(Table Removed)
The above results show the effect of use of combination of media in a sequential manner for carrying out the dissolution of the in-situ gel forming injectable depot liquid composition of Olanzapine. With 0.01 N HCI (up to 12hr) and 0.01 N HCI with 4% ethyl acetate (12-48hr); the release is non uniform with sudden increase of the release in time interval of 12-15hr. With 0.01 N HCI (upto 12hr) and 0.1N HCI (12-48 hr), the release is non-uniform and comparatively less as compared to media containing 0.02N HCI for 12hr followed by 0.1NHCI for the next 36hr. The results indicate that the release is uniform, sustained and more than 80% in media containing 0.02N HCI for 12hr followed by 0.1NHCI for the next 36hr. Hence this media is best suited for providing the uniform release of Olanzapine for a sustained period of time and without the initial burst effect.

WE CLAIM:
1. An in-vitro dissolution method for an in-situ gel forming injectable depot liquid composition of Olanzapine, wherein the dissolution is performed according to USP dissolution method II (Paddle method, 75 rpm) employing 0.02N HCI as dissolution media for the first 12hr; followed by changeover to 0.1 N HCI for the next 36hr.
2. The in-vitro dissolution method according to claim 1, wherein the sampling is performed from 1hr of placing the composition in the dissolution media upto 48hr at regular intervals.
3. The in-vitro dissolution method according to any of claims 1 or 2, wherein the dissolution media is selected from water, simulated intestinal fluid, simulated saliva, hydrochloric acid, acetate buffer and phosphate buffer.
4. The in-vitro dissolution method according to claim 3, wherein the dissolution media contains a surfactant, selected from non-ionic, cationic and zwitterionic surfactants.
5. The in-vitro dissolution method according to claim 4, wherein the surfactant is selected from sodium dodecyl sulfate, Tween 80, chenodeoxycholic acid, glycocholic acid sodium salt, Tween 20, taurocholic acid and triton X-100.
6. The in-vitro dissolution method according to any of claims 1 or 2, wherein the dissolution media contains one or more of strong acids, strong bases, and salts, single or multiple conjugate acid base pairs, monoprotic and polyprotic electrolytes.
7. An in-vitro dissolution method for an in-situ gel forming injectable depot liquid composition of Olanzapine substantially exemplified and described herein.