Technical Field of the Invention
The present invention relates to a dry process for preparing stable pharmaceutical compositions of emtricitabine and combinations thereof. In particular, the compositions have reduced levels of desamino emtricitabine (a major degradation product of emtricitabine), total impurities and related substances.
Background of the invention
Emtricitabine, (-)-cis FTC, is a synthetic nucleoside analog and is chemically described as [5-fluoro-1(2R, 5S)-[2-(hydroxymethyl)-1,3-oxathiolan-5-yl]cytosine]. Emtricitabine is indicated, in combination with other antiretroviral agents for the treatment of HIV-1 infection in patients.
Emtricitabine is currently marketed by Gilead as EMTRIVA® capsules (200mg) and as 10mg/mL oral solution. It is also marketed in combination with tenofovir disoproxil fumarate as TRUVADA® fixed dose combination tablets comprising 200mg emtricitabine and SOOmg tenofovir disoproxil fumarate and as ATRIPLA™ fixed dose combination tablets comprising 200mg emtricitabine, SOOmg tenofovir disoproxil fumarate and 600mg efavirenz.
US 5,814,639 specifically claims emtricitabine and pharmaceutical composition comprising the same in a pharmaceutically acceptable carrier or diluent. US 5,210,085 relates to a method for treating a human having an HIV infection comprising administering to the human an effective HIV treatment amount of emtricitabine and its monophosphate, diphosphate and triphosphate derivatives and pharmaceutically acceptable salts of the same. It also describes the administration of emtricitabine and its derivatives in a pharmaceutically acceptable carrier or diluent such as liposomal suspension. US 5,914,331 relates to derivatives of emtricitabine, its mono, di, triphosphate esters, salts and pharmaceutical compositions comprising the same.
PCT application WO 04/064845 discloses a composition comprising a combination of emtricitabine and tenofovir disoproxil fumarate. In the examples described therein, the fixed dose combination tablets of emtricitabine and tenofovir are manufactured using wet granulation techniques. It further describes chemically stable combinations of

emtricitabine and tenofovir disoproxil fumarate with a third antiviral agent which is selected from non-nucleoside reverse transcriptase inhibitors or protease inhibitors, more specifically, with atazanavir sulfate, efavirenz and Kaletra (combination of lopinavir and ritonavir). WO 04/064846 discloses a composition comprising a combination of emtricitabine and GS-7340. In the examples described therein, the fixed dose combination tablets of emtricitabine and GS-7340 are manufactured using wet granulation techniques. It further describes chemically stable combinations of emtricitabine and GS-7340 with a third antiviral agent which is selected from non-nucleoside reverse transcriptase inhibitors or protease inhibitors, more specifically, with atazanavir sulfate, Kaletra (combination of lopinavir and ritonavir) and efavirenz.
The chemical stability of active ingredients in a pharmaceutical formulation is of concern to minimize the generation of impurities and ensure adequate shelf life. As per the available literature, all the standalone or combination products of emtricitabine are manufactured using wet granulation process. Our experimentation with formulation of dosage forms of emtricitabine has revealed that the level of impurities increase significantly during wet granulation. Therefore, emtricitabine requires well-directed stability approaches to formulate pharmaceutical compositions with improved stability. Thus, there clearly exists a need to devise a suitable manufacturing process for the formulation of emtricitabine dosage forms containing emtricitabine alone or in combination with other antiretroviral agents so that the formulation remains stable during the entire shelf life with minimum levels of degradation products. The inventors have found that same level of impurities do not result when emtricitabine is formulated by dry manufacturing processes and the levels of desamino emtricitabine (a major degradation product of emtricitabine) are significantly reduced.
Summary of the Invention
In one general aspect, it relates to a dry process for preparing a stable pharmaceutical composition comprising emtricitabine wherein the process comprises mixing emtricitabine with one or more of pharmaceutically acceptable excipients and forming into a solid dosage form.
In one general aspect, it relates to a dry process for preparing a stable pharmaceutical composition comprising emtricitabine wherein the process comprises mixing

emtricitabine with one or more of pharmaceutically acceptable excipients and filling into a capsule.
In one general aspect, it relates to a dry process for preparing a stable pharmaceutical composition comprising emtricitabine wherein the process comprises mixing emtricitabine with one or more of pharmaceutically acceptable excipients and compressing into a tablet.
In another general aspect, it relates to a dry process for preparing a stable pharmaceutical composition comprising emtricitabine wherein the process comprises compacting emtricitabine alone or mixed with one or more of pharmaceutically acceptable excipients by roller compaction or slugging; sizing the compacts or slugs into granules by milling; optionally mixing the granules with one or more of pharmaceutically acceptable excipients and forming a solid dosage form.
In another general aspect, it relates to a dry process for preparing a stable pharmaceutical composition comprising emtricitabine wherein the process comprises compacting emtricitabine alone or mixed with one or more of pharmaceutically acceptable excipients by roller compaction or slugging; sizing the compacts into granules by milling; optionally mixing the granules with one or more of pharmaceutically acceptable excipients and filling the granules into a capsule.
In another general aspect, it relates to a dry process for preparing a stable pharmaceutical composition comprising emtricitabine wherein the process comprises compacting emtricitabine alone or mixed with one or more of pharmaceutically acceptable excipients by roller compaction or slugging; sizing the compacts into granules by milling; optionally mixing the granules with one or more of pharmaceutically acceptable excipients and compressing into a tablet.
In one embodiment of the above aspects, the solid dosage form contains other anti-retroviral drugs in combination with emtricitabine effective for the treatment of HIV infection.
In another general aspect, it relates to a dry process for the preparation of stable pharmaceutical composition comprising emtricitabine and tenofovir disoproxil fumarate

wherein the process comprises compacting emtricitabine and tenofovir disoproxil fumarate alone or mixed with one or more of pharmaceutically acceptable excipients by roller compaction or slugging; sizing the compacts into granules by milling; optionally mixing the granules with one or more of pharmaceutically acceptable excipients and forming a solid dosage form.
In another general aspect, it relates to a dry process for the preparation of stable pharmaceutical composition comprising emtricitabine and tenofovir disoproxil fumarate wherein the process comprises compacting emtricitabine and tenofovir disoproxil fumarate alone or mixed with one or more of pharmaceutically acceptable excipients by roller compaction or slugging; sizing the compacts into granules by milling; optionally mixing the granules with one or more of pharmaceutically acceptable excipients and compressing into a tablet.
Detailed Description of the Invention
"Emtricitabine" as recited herein means emtricitabine, and physiologically functional derivatives thereof. The term "physiologically functional derivative" includes any physiologically acceptable salt, ether, ester, prodrug, solvate, stereoisomer including enantiomer, distereomer, or stereoisomerically enriched or racemic mixture, and any other compound which upon administration to the recipient, is capable of providing (directly or indirectly) such a compound or an antivirally active metabolite or residue thereof. Emtricitabine may be present in an amount from about 100mg to 1000mg per unit dosage form.
The term "stable" as used herein refers to the chemical stability of emtricitabine in solid dosage forms when these dosage forms are stored under controlled temperature and humidity, for example, 40°C and 75% relative humidity. Emtricitabine has a relatively low pKa value which is indicative of its susceptibility to undergo acidic hydrolysis. Emtricitabine, with a pKa of 2.65 undergoes hydrolytic deamination of the 5-fluoro cytosine nucleobase to form desamino emtricitabine which is the major degradation product of emtricitabine. The other related substances produced are 5-fluoro cytosine, carboxylic acid impurities, lamivudine impurity, sulfoxide impurities along with some unknown impurities. As per the available literature, all the standalone or combination products of emtricitabine are manufactured using wet granulation process involving use

of solvents which results in a significant increase in the levels of impurities. This is clearly evident from the comparative stability data generated for emtricitabine capsules formulated by both wet and dry granulation techniques. In one instance, emtricitabine capsules when formulated by wet granulation had about 0.13% of desamino emtricitabine after storage in HOPE containers at 40°C and 75% relative humidity for one month. The total related substances were found to be about 0.3% for one month in same conditions. The same capsules when stored at 60°C for 15 days in HOPE containers had desamino emtricitabine content of about 0.26% and total related substances about 0.48%. On the contrary, when formulated by dry granulation, desamino emtricitabine was not detected (ND) after 1 month at 40°C and 75% relative humidity and the level of desamino emtricitabine at 60°C after 15 days was about 0.01%. Total related substances in the same capsules were about 0.18% after one month at 40°C and 75% relative humidity, and about 0.23% at 60°C after 15 days.
The term "pharmaceutical composition" as used herein includes solid dosage forms such as tablet, capsule, granules, pills, beads, and the like.
The stable pharmaceutical compositions besides containing emtricitabine may also contain other anti-retroviral drugs. The term "anti-retroviral drugs" as described herein includes drugs or compounds intended for treating, reversing, reducing or inhibiting retroviral infections, in particular infections caused by HIV. The anti-retroviral drugs may be selected from the various classes of drugs such as nucleoside, nucleotide or non-nucleoside reverse transcriptase inhibitors or protease inhibitors. Nucleoside reverse transcriptase inhibitors may include lamivudine, zidovudine, stavudine, abacavir, zalcitabine and didanosine. Nucleotide reverse transcriptase inhibitors may include adefovir, tenofovir, tenofovir disoproxil and its fumarate salt. Non-nucleoside reverse transcriptase inhibitors may include efavirenz, nevirapine and delavirdine. Protease inhibitors may include indinavir, nelfinavir, lopinavir, ritonavir, saquinavir, amprenavir, atazanavir, tipranavir and fosamprenavir.
The term "pharmaceutically acceptable excipients" as used herein include substances known in the art and may be one or more of diluents, binders, disintegrants, lubricants and glidants. The excipients are selected based on the desired physical aspects of the final composition.

Examples of diluents include one or more of any conventional diluents such as microcrystalline cellulose, lactose, mannitol, starch, pregelatinized starch, calcium phosphate, calcium sulfate, sorbitol, mannitol and the like.
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Examples of binders include polyvinylpyrrolidone, polyvinyl alcohol, cross-linked polyvinylpyrrolidone, cellulose gums (e.g. carboxymethyl cellulose, hydroxypropyl methylcellulose, hydroxypropyl cellulose), pregelatinized starch and the like.
Examples of disintegrants include microcrystalline cellulose, hydroxypropyl cellulose (HPC), carboxymethyl cellulose, cross linked carboxymethyl cellulose sodium, starches or modified starches such as sodium starch glycolate, corn starch, potato starch or pregelatinized starch, cross linked polymers such as crospovidone and the like.
Examples of lubricants and glidants include magnesium stearate, stearic acid, talc, colloidal silicon dioxide, calcium stearate, zinc stearate, and the like.
The dry process for manufacturing stable pharmaceutical compositions involves dry mixing of emtricitabine and optionally other anti-retroviral drug(s) with one or more of pharmaceutically acceptable excipients such as diluent, binder, disintegrant, lubricant and glidant and directly compressing into a solid dosage form such as tablet or filled into a capsule. Alternatively, the above mixture may also be subjected to dry granulation by compaction or slugging process well known in the art. The compaction of the drug or the mixture comprising the drug and excipient(s) into compacts may be carried out by slugging or by roller compaction, particularly suitable is roller compaction.
The roller compactor functions by uniformly applying pressure on a mixed powder blend by passing the blend between two counter-rotating rollers. The pressure imparted on the blend by the rollers compresses the powder into a compact, such as a sheet or ribbon, which is typically milled to produce granules.
In one general aspect of the process, emtricitabine is mixed with one or more of pharmaceutical excipients such as filler, binder, disintegrant and lubricant described above in a suitable blender. The mixing time can vary from about 10 to 60 minutes. The resultant blend can either be directly compressed into solid dosage form or compacted by roller compaction.

The resultant blend for compaction is subsequently transferred to a roller compactor in a known manner. The roller speed, roller gap width and force of compaction are then adjusted and the blend is fed through the roller compactor. The typical force and other conditions can be easily adjusted by the skilled in the art. For example, the compaction pressure may be between 15 to 230 bar or typically between 30 to 100 bar. For maintaining the steady output of the compact material from the roller compactor, the rollers may be rotated at a speed of between 3 to 13 rpm, particularly between 3 to 5 rpm. When in contact with the counter rotating rollers of the roller compactor, the compression force imparted on the blend by rollers converts the powdered form into a ribbon or compaction sheet. This compact sheet is fed to a mill, such as an oscillating mill, fitted with a screen. The screen can be selected with variable hole diameters depending upon the size of the granules required. After passing through the mill and the screen, the compact is converted into granules of the desired particle size distribution.
The granules obtained as above may be filled into capsules or packed in sachet. The granules can also be mixed with one or more of pharmaceutically acceptable excipients and compressed into tablets.
Alternative to roller compaction, slugging may be used for preparing granules. The process is simple, low cost and effective. Slugging may be carried out by means of a tablet press. The drug either alone or mixed with other excipients is precompressed on a heavy duty press. The slug that is formed is milled into granules, which in turn may be recompressed into tablet. The granules may also, optionally, be mixed with other extragranular excipients prior to compression into a tablet.
In another embodiment, the process comprises mixing emtricitabine, filler, binder, disintegrant and lubricant and compacting the mixture using roller compactor; milling and sizing the compacts into granules with a desired particle size distribution; mixing with lubricant and filled into a capsule.
In still another embodiment, the process comprises mixing emtricitabine, filler, binder, disintegrant and lubricant and compacting the mixture using roller compactor; milling and sizing the compacts into granules with a desired particle size distribution; mixing with one or more of fillers, binders, disintegrants and lubricants and filled into a capsule.

In still another embodiment, the process comprises mixing emtricitabine, filler, binder and lubricant and compacting the mixture using roller compactor; milling and sizing the compacts into granules with a desired particle size distribution; mixing with one or more of fillers, binders, disintegrants and lubricants and filled into a capsule.
In one embodiment, the process comprises compacting emtricitabine alone or mixed with one or more of pharmaceutically acceptable excipients using roller compactor; milling and sizing the compacts into granules with a desired particle size distribution; mixing with extragranular pharmaceutically acceptable excipient(s) and compressing into a tablet using appropriate tooling.
In still another embodiment, the process comprises compacting emtricitabine alone or mixed with one or more of pharmaceutically acceptable excipients by slugging; milling and sizing the slugs into granules with a desired particle size distribution; optionally mixing the granules with one or more of fillers, binders, disintegrants and lubricants and filling into a capsule.
In still another embodiment, the process comprises compacting emtricitabine alone or mixed with one or more of pharmaceutically acceptable excipients by slugging; milling and sizing the slugs into granules with a desired particle size distribution; optionally mixing the granules with one or more of fillers, binders, disintegrants and lubricants and compressing into a tablet using appropriate tooling.
In one embodiment, the process comprises compacting emtricitabine and another anti-retroviral drug alone or mixed with one or more of fillers, binders, disintegrants and lubricants, milling and sizing the compacts into granules with a desired particle size distribution and filling into a capsule dosage form.
In another embodiment, the process comprises compacting emtricitabine and another anti-retroviral drug alone or mixed with one or more of pharmaceutically acceptable excipients using roller compactor; milling and sizing the compacts into granules with a desired particle size distribution; mixing with extragranular pharmaceutically acceptable excipient(s) and compressing into a tablet.

In yet another embodiment, the process comprises compacting emtricitabine and another anti-retroviral drug alone or mixed with one or more of fillers, binders, disintegrants and lubricants, milling and sizing the compacts into granules with a desired particle size distribution; mixing with one or more of diluents, disintegrants and lubricants and compressing into a tablet.
When the solid dosage form is a tablet, then it may additionally be coated with coating compositions like Opadry® AMB (with or without a non aqueous subcoat) sold by Colorcon to impart moisture protection on stability. Such a coating may comprise about 3 -10% w/w of the tablet. The tablet may also be coated with coating compositions like
Opadry® or Lustreclear® sold by Colorcon using non-aqueous or aqueous systems, preferably non-aqueous system to impart aesthetic appeal as well as a barrier to the external environment. Such a coating may comprise about 3-10%w/w of the tablet.
In one embodiment, emtricitabine is formulated in combination with tenofovir disoproxil fumarate by dry granulation method to obtain chemically stable fixed dose combination tablets. The said composition has reduced levels of desamino emtricitabine, monoester of tenofovir, total impurities and related substances. Tenofovir disoproxil fumarate with a relatively low pka value of 3.75, is subject to hydrolytic deamination of the exocyclic amine of the adenine nucleobase, and to hydrolysis of one or both of the POC ester groups. The major degradation product of tenofovir disoproxil fumarate is the monoester of tenofovir. Other related substances include 6-amino purine and tenofovir. Therefore, it is desirable to develop a suitable process for the formulation of a therapeutic combination dosage forms of emtricitabine and tenofovir disoproxil fumarate, with adequate stability and minimum of impurities.
In a preferred embodiment, the stable pharmaceutical composition comprising emtricitabine and tenofovir disoproxil fumarate and optionally, one or more of pharmaceutically acceptable excipients are formulated by dry granulation process. The dry granulation process comprising the steps of:
a) blending emtricitabine and tenofovir disoproxil fumarate and one or more of
pharmaceutically acceptable excipients;
b) compacting the material of step (a) using roller compactor;
c) sizing the compacted material of step (b) into granules, and;

d) optionally, mixing the sized granules of step (c) with one or more of pharmaceutically acceptable excipients and then compressing into tablets.
The said composition comprising emtricitabine and tenofovir disoproxil fumarate when stored at 40°C and 75% relative humidity did not show any detectable amounts of desamino emtricitabine after one month and less than about 0.05% of desamino emtricitabine after three months. Storage at 60°C for 15 days also resulted in non-detectable amounts of desamino emtricitabine. Percentage of total related substances in the dosage form was less than about 1.5% after one month, less than about 2.2% after three months; and less than about 1.1% after storage at 60°C for 15 days. The tablets had less than about 0.8% of monoester of tenofovir after one month and less than about 1.5% after three months when stored at 40°C and 75% relative humidity. Storage of the tablets at 60°C for 15 days produced less than about 0.8% of monoester of tenofovir. In comparison, the wet granulation process resulted in higher impurity levels. Desamino emtricitabine levels were 0.56% and 1.66% after one and three months respectively when stored at 40°C and 75% relative humidity in HOPE containers. The percentage of total related substances was about 4.8% after one month and about 8.5% after three months at 40°C and 75% relative humidity. The levels of monoester of tenofovir were 3.2% after one month and 4.7% after three months under the same storage conditions.
The following examples are illustrative of the invention but are not intended to be construed as limiting the invention.
Example 1: Comparitive example of emtricitabine capsules prepared bv wet and dry granulation methods

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Procedure: Example 1a
Emtricitabine, microcrystalline cellulose and crospovidone were mixed in a rapid mixer granulator and granulated with polyvinylpyrrolidone solution. The granules were dried and mixed with magnesium stearate and filled into a capsule.
Procedure: Example 1b
Emtricitabine, microcrystalline cellulose and polyvinylpyrrolidone were mixed in a blender and lubricated with magnesium stearate. The lubricated blend was compacted on a roller compactor. The compacts were sized into granules of appropriate sizes and mixed with crospovidone and magnesium stearate and filled into a capsule.
The capsules were evaluated for the presence of impurities after storage in HOPE containers at 40°C/75% relative humidity and at 60°C after suitable time periods using HPLC. The results of this measurement are listed as percentages (w/w) in Tables 1 and 2. The results clearly indicate the role of moisture in the degradation of emtricitabine during the shelf life of the composition.
Table 1: Results of stability evaluation of emtricitabine capsules prepared as per example 1a by wet granulation method

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Table 2: Results of stability evaluation of emtricitabine capsules prepared as per example 1b by dry granulation method

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Example 2: Comparative example of emtricitabine and tenofovir disoproxil fumarate fixed dose combination tablets manufactured using wet and dry granulation methods

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Procedure: Example 2a
Emtricitabine, tenofovir disoproxil fumarate, microcrystalline cellulose, lactose and crosslinked carboxymethyl cellulose sodium were mixed in a rapid mixer granulator and granulated with a solution of pregelatinized starch prepared in water. The granules were lubricated with magnesium stearate and mixed with extragranular microcrystalline cellulose, crosslinked carboxymethyl cellulose sodium and lubricated with magnesium stearate and compressed into a tablet.
Procedure: Example 2b
Emtricitabine, tenofovir disoproxil fumarate, microcrystalline cellulose and lactose were mixed in a blender and then lubricated with magnesium stearate. The lubricated blend was compacted on roller compactor. The compacts so obtained were sized into granules of appropriate size using oscillating granulator. The sized granules were mixed with extragranular microcrystalline cellulose, crosslinked carboxymethyl cellulose and magnesium stearate and compressed into a tablet.
The tablets obtained above were subjected to stability evaluation at 40°C and 75% relative humidity over a period of 3 months in HOPE containers. The results of this measurement are listed as percentages (w/w) in Tables 3 and 4. The results clearly indicate the role of moisture in the degradation of emtricitabine as well as tenofovir disoproxil fumarate during the shelf life of the composition.
Table 3: Results of stability evaluation of emtricitabine and tenofovir disoproxil fumarate fixed dose combination tablets prepared as per the example 2a by wet granulation over a period of 3 months at 40°C and 75% relative humidity

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Table 4: Results of stability evaluation of emtricitabine and tenofovir disoproxil fumarate fixed dose combination tablets prepared as per example 2b by dry granulation over a period of 3 months at 40°C and 75% relative humidity.
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WE CLAIM:
1) A dry process for preparing a stable pharmaceutical composition comprising
emtricitabine wherein the process comprises mixing emtricitabine with one or
more pharmaceutically acceptable excipients and forming into a solid dosage
form.
2) The process according to Claim 1; wherein the process comprises direct
compression or dry granulation.
3) The process according to Claim 2; wherein the said process is dry granulation
and comprises compacting emtricitabine alone or mixed with one or more of
pharmaceutically acceptable excipients by roller compaction or slugging; sizing
the compacts or slugs into granules by milling; optionally mixing the granules
with one or more of pharmaceutically acceptable excipients and forming a solid
dosage form.
4) The process according to Claim 1; wherein the pharmaceutically acceptable
excipients are selected from diluent(s), binder(s), disintegrant(s), lubricant(s)
and glidant(s) as herein described.
5) The process according to Claim 1, wherein the solid dosage form is a capsule.
6) The proc'ess according to Claim 1, wherein the solid dosage form is a tablet.
7) The process according to Claim 1; wherein process further comprises mixing of
one or more of other antiretroviral drugs with emtricitabine.
8) The process according to Claim 7, wherein the other antiretroviral drugs are
selected from nucleoside reverse transcriptase inhibitors, nucleotide reverse
transcriptase inhibitors, non-nucleoside reverse transcriptase inhibitors and
protease inhibitors.

9) The process according to Claim 8; wherein the nucleotide reverse transcriptase
inhibitor is selected from tenofovir, tenofovir disoproxil and its fumarate salt.
10) A dry process for the preparation of a solid dosage form comprising
emtricitabine alone or in combination with other antiretroviral drugs substantially
as described herein.