WO2009116055A1

WO2009116055A1 - Lamivudine : zidovudine : water 1 : 1 : 1 cocrystal

Info

Publication number: WO2009116055A1
Application number: PCT/IN2008/000276
Authority: WO
Inventors: Bhairab Nath Roy; Girij Pal Singh; Dhananjai Srivastava; Harishchandra Sambhaji Jadhav; Gautam R. Desiraju; Prashant M. Bhatt
Original assignee: Lupin Limited
Priority date: 2008-03-17
Filing date: 2008-04-30
Publication date: 2009-09-24

Abstract

Co-crystal of lamivudine with zidovudine comprising one molecule each of lamivudine, zidovudine and water; having distinct X-ray diffraction peaks at 2θ of 9.57, 11.45, 13.68, 15.57, 16.49, 18.35, 18.82, 20.45, 22.18, 22.78, 24.52, 24.99, 26.36, 26.55, 26.58 ± 0.2°. Process for preparation of co-crystal of lamivudine with zidovudine comprising of trituration of equimolar quantities of Lamivudine and zidovudine in presence of water at ambient temperature, optionally adding organic solvent during trituration, and drying the product. Process for preparation of co-crystal of lamivudine with zidovudine comprising stirring equimolar quantities of lamivudine and zidovudine in an organic solvent in presence of water at ambient temperature, evaporating solvents of the solution, allowing crystallization of product with optional seeding, isolating co-crystals and drying. Pharmaceutical composition comprising therapeutically effective amount of co-crystals of lamivudine, zidovudine. Use of therapeutically effective amount of co-crystal Zidovudine, Lamivudine for manufacture of medicament for treatment of HIV infections of humans.

Description

LAMIVUDINE : ZIDOVUDINE : WATER 1 : 1 : 1 COCRYSTAL

Field of Invention:

The invention relates to pharmaceutical co-crystal of Lamivudine with Zidovudine and the process of preparation thereof.

Back Ground:

To be a drug product not only the active pharmaceutical ingredient (API) should have desirable pharmacological and pharmacokinetic properties but also must be amenable for formulation into a suitable dosage form so that on ingestion it also gives desirable pharmacological, pharmacokinetic and pharmacodynamic effects.

The physicochemical characteristics of API more often than not determines formulation development work.

The important characteristics of API amongst other include (a) optimum solubility and dissolution rate (b) stability, should not be degraded and converted to other substance both by physical factors like heat, light as well as chemical interaction (c) must have desirable flow properties, bulk density and should not stick to the walls of the vessel, and most importantly (d) should be bioavailable / bioequivalent. All of these characters of an API are essentially dependant on its crystal structure.

As mentioned earlier crystal structure is a center point of solid stage manipulation and formulation development of API. Hence attempts are being made to obtain a crystal structure that is a desired polymorph. Therefore attempts have been made, though pain taking, to obtain crystal structure, which would give desirable dosage forms having all the properties mentioned hereinbefore.

When crystallization of a single substance takes place, identical molecules are incorporated in the crystal lattice. In short, a crystal lattice contains the same molecules arranged in periodic order packed with the help of non-covalent bonds like hydrogen bonds, co-ordinate bonds, van der Waals forces, etc.

However, when two or more molecules are crystallized together, the crystallization could be homo or hetero. When it is hetero, the formation of a crystal lattice (A. B) is called as co-crystal.

B

A

A AB

A AB - - -B- - ^•A- -B

B

AB AB - - - -A- - B-- -A

B B

A A AB AB B- - A- - B

B

A

B

Such incorporation of a chemically distinct molecule could drastically change the physicochemical characteristics like solubility, dissolution rate, stability, etc. and hence can alter the bioavailability of the active pharmaceutical ingredient. For example US 2007/0059356 describes how effectively co-crystallization enabled to convert the injectable API to conventional oral solid dosage form. In short effect of co-crystallization can be so dramatic to reach a far reaching of consequences and ramification.

It would not be out of place to review the advancement in the research in co-crystals in view of active pharmaceutical ingredients.

Co-crystals are crystals that contains two or more non-identical molecules. Various co-crystals were reported in Etter MC, and Adsmond DA "The use of co- crystallization as a method of studying hydrogen bond preferences of 2- aminopyridine" J. Chem. Soc, Chem. Commun. (1990) 589-591 , Etter MC, et al., "Graph-set analysis of hydrogen-bond patterns in organic crystals" Acta Crystallogr. Sect. B, Struct. Sci. (1990), B46 256-262; Etter MC, et al., "Hydrogen bond directed co-crystallization and molecular recognition properties of diarylureas" J. Am. Chem. Soc. (1990) 112 8415-8426, which are incorporated herein by reference in their entireties. The following articles are also incorporated herein by reference in their entireties: Carl HG and Hans PH₁ ¹¹On the inclusion of solvent molecules in the crystal structures of organic compounds"; Acta Cryst. (2000), B56, 625-534; SenthilKumar VS, Nangia A, et al., "Molecular Complexes of Some Mono- and Dicarboxylic Acids with fra/7S-l,4,-Dithiane-l,4-dioxide" Crystal Growth & Design (2002), 2(4), 325 - 328; and Desiraju G. R., "Crystal and co-crystal" Cryst.. Eng. Comm. (2003), 5, 466-467.

By co-crystallizing an active agent with a guest, one creates a new solid form which has unique properties compared to the existing solid forms of that active agent. For example, a co-crystal may have different dissolution and solubility properties than the active agent itself or as a salt. The guest molecule is often a pharmaceutically acceptable compound (which could also be an API). Co-crystals containing APIs can be used to deliver APIs therapeutically. New drug formulations comprising co- crystals of APIs with pharmaceutically acceptable guests may have superior properties over existing drug formulations (US 2007/0059356 and WO 2007/067727). Active agents and guests may also include nutraceuticals, agricultural chemicals, pigments, dyes, explosives, polymer additives, lubricant additives, photographic chemicals, and structural and electronic materials.

It has been speculated (Chem. Commun. 2005, 4601-4603) that the formation of co- crystal might considerably reduce the possibility of polymorphism in API. The authors found that among the approximately 1450 structures of hydrogen-bonded co-crystals in the Cambridge Structure Database only 11 entries were polymorphic. This behavior of the co-crystals can be attributed to the stronger intermolecular interactions between the active molecule and the host molecule that impart physical stability to the solid form. Reduction in chances of unanticipated polymorphism in solid co-crystals of the active ingredient would minimize the problems faced by the formulation chemists during manufacture of dosage forms of metastable solid forms.

Combivir® is a pharmaceutical fixed dose combination containing Lamivudine and Zidovudine for treatment of HIV infection. Fixed dose combination of Lamivudine and Zidovudine is disclosed in US patent number 5,627,186 and 5,859,021. The ratio of Lamivudine as to Zidovudine varied from 1:2 to 1:1 by weight. During formulation both the drugs were physically mixed along with the excipients and compressed to form a tablet.

US 5905082 describes two polymorphic modifications of Lamivudine viz form I and II. and WO20071 _,19248 describes a novel polymorph III. Polymorph III and I are metastable hydrated forms and polymorph Il is an anhydrous form. Though polymorph Il is thought to be the thermodynamically most stable form, form I and form III can also be formulated into a solid dosage form. As described in WO2007119248 all these polymorphic forms of Lamivudine get converted to other polymorphs under certain conditions. Moreover, form I is needle shaped and therefore poses problems in mixing and has poor flow property and bulk density. Therefore, it is desirable to make a stable crystal form of Lamivudine having better flow property and bulk density, thereby possessing better manufacturability.

During the crystallization study of Lamivudine, the present inventors have found that interestingly Lamivudine forms a 1:1:1 mole co-crystal with Zidovudine and water, and surprisingly, the co-crystal formed is stable when stirred with either water or any other solvents like isopropanol and the DSC thermogram shows single endothermic peak at about 100°, which shows that it is a stable crystal form, i.e. does not undergo modification on heating. Objects of the invention

Thus an object of the present invention is to provide a novel co-crystal monohydrate of Lamivudine with Zidovudine.

Another object of the present invention is to provide a physically stable crystal form of Lamivudine co-crystallized with Zidovudine.

A further object of the present invention is to provide a process for preparation of a novel co-crystal of Lamivudine with Zidovudine using the eco-friendly solvent "water" and using minimum quantity of solvent thereby reducing the generation of effluents.

Summary of invention

Thus in the present invention there is provided a co-crystal of Lamivudine with 1 molecule of Zidovudine and one molecule of water having characteristic powder X- ray difractogram as shown in figure 1 with characteristic 2Θ values as given in Table -I.

According to another aspect there is provided a process of preparation of co-crystal of 1 molecule each of Lamivudine, Zidovudine and water by wet grinding Lamivudine and Zidovudine in presence of water.

Brief description of the Accompanying drawings

Figure 1 : powder X-ray diffractogram of co-crystal. Figure 2: DSC of co-crystal Figure 3: Powder X-ray diffractogram of equimolar physical mixture of Lamivudine and Zidovudine

Figure 4: FTIR spectra of co-crystal of Lamivudine.

Figure 5: FTIR spectra of equimolar physical mixture of lamivudine and zidovudine. Figure 6: TGA of co-crystal Figure 7: ORTEP diagram of co-crystal

Figure 8. Different intermolecular interactions of zidovudine molecule in the crystal structure of co-crystal.

Figure 9. Different intermolecular interactions of lamivudine molecule in the crystal structure of co-crystal.

Figure 10. 1 D ribbon type arrangement of lamivudine and ziodvudine molecules in the crystal structure of co-crystal.

Figure 11. 1 D ribbons from perpendicular view and interconnectivity between them in the crystal structure of co-crystal. Figure 12. Simulated PXRD of co-crystal

Figure 13: DSC thermogram of crystalline form I of Lamivudine

Figure 14 TGA thermogram of crystalline form I of Lamivudine.

Figure 15: DSC thermogram of crystalline form Il of Lamivudine

Figure 16: TGA thermogram of crystalline form Il of Lamivudine Figure 17: DSC thermogram of crystalline form III of Lamivudine

Figure 18: TGA thermogram of crystalline form III of Lamivudine.

Figure 19: DSC thermogram of Zidovudine

Figure 20: TGA thermogram of Zidovudine.

Figure 21 : DSC thermogram of equimolar physical mixture of Lamivudine and Zidovudine

Figure 22: TGA thermogram of equimolar physical mixture of Lamivudine and

Zidovudine

Description of the invention: Three polymorphic modifications of Lamivudine viz form I, II. and III get interconverted under certain conditions.. Polymorphic form I and III are the metastable forms according to the DSC thermogram, both of them are converted to polymorphic form Il (as described in page 1 to 5 of WO2007/119248). Form I and Il when stirred with water get converted to polymorphic form III (see page 5 and examples 11 and 12 of WO2007/119248). Hence, attempts to formulate form I or Il using water as a solvent would result in form III. These interconversions may cause instability to the pharmaceutical formulations.

The co-crystal of Lamivudine with Zidovudine is stable when stirred in water and other organic solvents as revealed by powder X ray diffraction and other solid state properties like FTIR, DSC and TGA. The DSC thermogram (Figure 2) of the co- crystal shows a single peak of the endothermic deformation corresponding to its melting point. There is no other peak in DSC, which shows that the co-crystal is stable on heating.

When the experiments were carried out to study the stability of the co-crystal in various solvents like water and isopropanol, no change in the crystal structure of the co-crystal was observed. Hence, there would be no restriction in choosing a solvent for the formulation of lamivudine.

The solid-state properties like powder X-ray diffractogram and FTIR of the co-crystal are distinct over the equimolar physical mixture of Lamivudine and Zidovudine. The comparative data for the physical mixture and the co-crystal of Lamivudine are provided in Table I.

The co-crystal of Lamivudine has better flow property and bulk density, which are important parameters for formulation (Table II).

Table I:

Table Il

Thermogravimetric analysis (as shown in fig. 6) of the co-crystal of Lamivudine shows 1.2 to 1.9 % single step loss of weight. Moisture content of this crystal form by Karl Fischer titration is in the range of 3.5 to 4.0%, which confirms presence of approximately equimolar quantities of Lamivudine, Zidovudine and water in the co- crystal.

The co-crystal monohydrate is obtained by pulverization of stoichiometric quantities of Lamivudine and Zidovudine in presence of water. The co-crystal hydrate can also

^$ measured as per the procedure provided on page 317 of 'The Theory and Practice of Industrial Pharmacy' by Leon Lachman et al., Third Ed. Varghese Publishing House, Bombay; (1987) be obtained by dissolving Lamivudine and zidovudine in an organic solvent containing water, concentrating the solution and allowing the concentrated solution to stand, which can optionally be seeded with the co-crystal.

For the study by single crystal X-ray crystallography methods the single crystal of the co-crystal was developed as follows: 22.9 mg of lamivudine and 26.7 mg of zidovudine were taken in a sample vial. 1 ml ethanol was added and the mixture was warmed for 2-3 minutes until a clear solution was obtained. The solution was allowed to evaporate slowly for 2 days. Diffraction quality single crystals were obtained from the crystalline mass obtained after 2 days.

The single crystal X-ray analysis is carried out using SMART APEX CCD diffractometer by full-matrix least-squares refinement on F²; goodness of fit on F² was 1.033. A total of 11952 reflections were measured on the diffractometer with monochromatised Mo-Ka radiation. The data was collected at θ ranging from 1.10 to 26.06°. The structure was solved by direct methods and the non-hydrogen atoms were refined anisotropically. All H atoms were refined isotropically. Refinement converged to give R1 = 0.0377, wR2 = 0.0975. Minimum residual electron density was -0.232 e. A^"3 and maximum residual electron density was 0.336 A^"3. The data is as shown in Table III and figures 7 to 11.

Crystal structure obtained by single crystal X-ray diffraction analysis (Fig. 7) reveals the association of one molecule each of Lamivudine, Zidovudine and water in the co- crystal with the help of hydrogen bonds as follows:

The crystal structure of the co-crystal has a large number of intermolecular interactions present. Each zidovudine molecule forms five different interactions with three different lamivudine molecules (N-H...O, O-H...O) and two different water molecules (N-H... O₁ O-H...O) as shown in figure 8. Each lamivudine molecule forms four different interactions with three different zidovudine molecules (N-H...O, O-H...O) and one water molecule (O-H...N) as shown in figure 9. Lamivudine, zidovudine and water make an infinite 1 D ribbon-type arrangement as shown in figure 10. These ribbons are further connected by O-H...O interactions between zidovudine and lamivudine as shown in figure 11.

Powder X-ray diffractogram generated from computer simulation of single crystal X- ray data is shown in figure 12.

The single crystal X-ray diffraction data obtained for co-crystal of Lamivudine is tabulated in Table III

Table III

Attempts to obtain an anhydrous co-crystal were unsuccessful since it is evident from the single crystal X-ray diffraction data of co-crystal that water molecule plays an important role in formation of hydrogen bonds between lamivudine and zidovudine. Comparative thermal analysis data is tabulated in Table IV

Table IV

(a) US5905082; (b) Journal of Pharm. Sci VoI 85 (2), page 195 (1996); (c) WO2007119248; (d) J. Org. Chem. 29, 2076 (1964); (e) J. Org. Chem. 38, 4299 (1973)

The solubilities of the co-crystal and equimolar physical mixture in methanol are comparable. There is a slight decrease in the aqueous solubility of the co-crystal as compared to that of the physical mixture. Comparative solubility data of the co- crystal and the physical mixture at a temperature of 25 ± 0.5 ⁰C are provided in table V.

Table V

Pharmaceutical formulations suitable for administration may conveniently be presented as discrete units such as capsules, cachets or tablets each containing a predetermined amount of the co-crystal or combinations of the co-crystal with other antiviral compounds or co-crystals thereof.

Lamivudine polymorphs I, Il and III were prepared for comparison by referring to the examples provided in US 5905082 and WO2007/119248. The present invention is ' illustrated in more detail by referring to the following Examples, which are not to be construed as limiting the scope of the invention. The term 'Lamivudine¹ in the examples refers to Lamivudine form Il unless specified.

Example 1:

458 mg of lamivudine and 534 mg of zidovudine were taken in a mortar and pestle and the mixture was triturated for 5 minutes to make a homogeneous mixture. 5-6 drops of ethanol and 5-6 drops of water were added to mixture at that stage and the mixture was then vigorously ground for a subsequent 15 minutes. The product obtained was further dried at 4O⁰C in vacuum drier for four hours. Yield: 0.992 gm

The melting point is 94 - 95 ⁰C.

FTIR [KBr] (cm^"1): 3532, 3414, 3310, 3219, 3087, 3014, 2956, 2920, 2832, 2160, 2093, 1713, 1642, 1524, 1498, 1473, 1436, 1269, 1104, 1053, 827, 782, 758, 741 , 619, 601 , 563, 496. (Figure 4)

The powder X-ray diffraction analysis shows peaks at about 9.57, 10.15, 11.45, 13.11 , 14.36, 15.52, 15.92, 16.49, 16.75, 18.00, 18.36, 18.83, 20.45, 20.80, 21.36, 22.18, 22.24, 22.79, 23.87, 24.52, 24.99, 25.41 , 25.72, 26.37, 26.59, 27.02, 27.12, 27.54, 28.17, 28.55, 28.79, 30.20, 30.86, 31.36, 32.13, 32.67, 33.30, 33.58, 33.86, 34.96, 35.85, 36.15, 36.45, 36.99, 38.17, 38.85 +0.2 degrees two theta. (Figure 1). The data/difractogram is superimposable with the one generated from single crystal data via computer simulation (Figure 12) The differential scanning calorimetric analysis shows a single peak of the endotherm at 101.85⁰C (Fig. 2).

The thermogravimetric analysis exhibits a one-step weight loss of 1.45 % between 8O⁰C to 100⁰C (Fig. 6) and Karl Fischer titration results in a moisture content of 3.60%.

Example 2 1.15 gm of lamivudine and 1.34 gm of zidovudine were taken in a mortar and pestle and the mixture was triturated for 5 minutes to make a homogeneous mixture. 5-6 drops of methanol and 5-6 drops of water were added to mixture at that stage and the mixture was then vigorously ground for a subsequent 20 minutes. The product obtained was further dried at 40⁰C in vacuum drier for four hours. Yield: 2.49 gm

The melting point of resultant material is 94 - 95°C.

Powder X-ray diffraction pattern and FTIR spectra is superimposable with that of the co-crystal as obtained in Example 1.

Example 3

1.15 gm of lamivudine and 1.34 gm of zidovudine were taken in a mortar and pestle and the mixture was triturated for 5 minutes to make a homogeneous mixture. 5-6 drops of ethanol and 5-6 drops of water were added to mixture at that stage and the mixture was then vigorously ground for a subsequent 15 minutes. The resulting material was then transferred to a 100 ml round bottom flask. 20 ml of distilled ethanol and 5 ml of distilled water was added and the mixture was stirred at 60 ⁰C for 1hour. The resulting solution was transferred to a 250 ml conical flask and allowed to evaporate slowly. Seed crystals of the co-crystal were added to the solution after 2 days. The crystalline mass obtained after one more day was filtered. The product obtained was further dried at 4O⁰C in a vacuum drier for four hours. Yield 2.3 gm

The melting point of resultant material is 94 - 95°C.

Powder X-ray diffraction pattern and FTIR spectra were superimposable with that of the co-crystal as obtained in Example 1.

Example 4

1.15 gm of lamivudine and 1.34 gm of zidovudine were taken in a 100 ml round bottom flask. 15 ml of distilled methanol and 5 ml of distilled water were added. The solution was concentrated in a rotavapor at around 80 ⁰C. The resulting solution (« 10 ml) was allowed to stand. The crystalline mass obtained after a few hours was filtered. The product obtained was further dried at 4O⁰C in vacuum drier for four hours. Yield: 2.25 gm

The melting point of the resultant material is 94 - 95°C.

Powder X-ray diffraction pattern and FTIR spectra are superimposable with that of the co-crystal as obtained in Example 1.

Example 5

1.15 gm of lamivudine and 1.34 gm of zidovudine were taken in a 100 ml round bottom flask. 15 ml of distilled methanol and 5 ml of distilled water was added. The solution was concentrated in rotavapor at around 80 "C. Resulting solution (« 10 ml) was allowed to stand and seed crystals of co-crystal were added into it. Crystalline mass obtained after around 1 hour was filtered. The product obtained was further dried at 4O⁰C in vacuum drier for four hours. Yield: 2.3 gm The melting point of the resultant material is 94 - 95⁰C.

Example 6

1.15 gm of lamivudine and 1.34 gm of zidovudine was taken in a 100 ml round bottom flask. 15 ml of distilled ethanol and 1.5 ml of distilled water was added in to it. The solution was concentrated in rotavapor at around 95 ⁰C. The resulting solution (« 7 ml) was allowed to stand. The crystalline mass obtained after few hours was filtered. The product obtained was further dried at 40⁰C in vacuum drier for four hours. Yield: 2.3 gm

The melting point of the resultant material is 94 - 95°C.

Example 7

4.58 gm of lamivudine and 5.34 gm of zidovudine were taken in a 100 ml round bottom flask. 50 ml of distilled ethanol and 5 ml of distilled water were added. The solution was concentrated in rotavapor at around 95 ⁰C. The resulting solution (» 15 ml) was allowed to stand and seed crystals of co-crystal were added. The crystalline mass obtained after one hour was filtered. The product obtained was further dried at 4O⁰C in a vacuum drier for four hours. Yield: 9.8 gms

The melting point of the resultant material is 94 - 95°C. Powder X-ray diffraction pattern and FTIR spectra are superimposable with that of the co-crystal as obtained in Example 1.

Example 8 1.15 gm of lamivudine and 1.345 gm of zidovudine were taken in a 100 ml round bottom flask. 11 ml of acetone and 4 ml of distilled water were added. The mixture was stirred for 10 minutes to make a homogeneous clear solution. The solution was allowed to evaporate for 2 days. A crystalline mass was obtained. The product obtained was further dried at 40⁰C in a vacuum drier for four hours. Yield: 2.49 gm

The melting point of the resultant material is 94 - 95°C.

Example 9

1.15 gm of lamivudine and 1.345 gm of zidovudine were taken in a 100 ml round bottom flask. 11 ml of acetonitrile and 4 ml of distilled water were added. The mixture was stirred for 10 minutes to make a homogeneous clear solution. The solution was allowed to evaporate for 2 days. The product obtained was further dried at 40⁰C in a vacuum drier for four hours. Yield: 2.60 gm

The melting point of the resultant material is 94 - 95°C.

Powder X-ray diffraction pattern and FTIR spectra are superimposable with that of the co-crystal as obtained in Example 1. Example 10

1.15 gm of lamivudine and 1.34 gm of zidovudine were taken in a mortar and pestle and the mixture was triturated for 5 minutes to make a homogeneous mixture. 11 drops of acetone and 4 drops of water were added to the mixture at this stage and the mixture was then vigorously ground for a subsequent 20 minutes. The product obtained was further dried at 4O⁰C in a vacuum drier for four hours. Yield: 2.49 gm.

The melting point of the resultant material is 94 - 95°C.

Example 11

1.15 gm of lamivudine and 1.34 gm of zidovudine were taken in a mortar and pestle and the mixture was triturated for 5 minutes to make a homogeneous mixture. 11 drops of acetonitrile and 4 drops of water were added to the mixture at this stage and the mixture was then vigorously ground for a subsequent 20 minutes. The product obtained was further dried at 4O⁰C in vacuum drier for four hours. Yield: 2.49 gm

The melting point of the resultant material is 94 - 95⁰C.

Example 12:

1.15 gm of lamivudine and 1.34 gm of zidovudine were taken in a mortar and pestle and the mixture was triturated for 2 minutes to make a homogenous mixture. 2 ml of ethanol and 0.5 ml of water were added to the mixture in 4 portions and ground for 1 hour. The product obtained was further dried at 40⁰C in a vacuum drier for four hours. Yield: 2.49 gm

The melting point of the resultant material is 94 - 95⁰C.

Example 13: 1.15 gm of lamivudine and 1.34 gm of zidovudine were taken in a mortar and pestle and the mixture was triturated for 5 minutes to make a homogeneous mixture. 5-6 drops of water were added to the mixture and vigorously ground for a subsequent 20-30 minutes. The sample was then dried under vacuum at 40 ⁰C for 4 hours. Yield: 2.48 gm.

The melting point of the resultant material is 94 - 95°C.

Example 14:

1.15 gm of lamivudine and 1.34 gm of zidovudine were taken in a mortar and pestle.

The solid material was triturated and blended homogeneously for around 20 minutes to obtain 2.49 gm of a homogeneous physical mixture of equimolar quantities of lamivudine and zidovudine.

The melting point is 112 - 115 ^βC. FTIR [KBr] (cnT¹): 3461 , 3329, 3184, 3029, 2825, 2117, 2083, 1672, 1613, 1487, 1399, 1360, 1336, 1316, 1282, 1259, 1181, 1160, 1142, 1089, 1059, 1031, 918, 897, 851 , 806, 788, 763, 734, 632, 593, 562, 538, 495. (Figure 5)

X-ray powder diffraction analysis shows peaks at about 8.92, 10.04, 10.68, 12.15, 13.39, 14.28, 14.75, 15.60, 15.82, 15.97, 16.81, 17.20, 17.53, 17.88, 18.24, 19.37, 19.66, 20.15, 20.61 , 20.68, 20.88, 21.15, 21.43, 21.49, 21.81, 22.33, 22.76, 23.00, 23.26, 23.74, 24.23, 24.42, 24.92, 25.00, 25.69, 26.48, 27.21 , 27.47, 27.89, 28.40, 28.73, 29.46, 29.72, 30.19, 31.45, 31.53, 31.81 , 32.39, 32.59, 33.12, 33.99, 34.80, 35.19, 35.52, 36.19, 36.95, 37.25, 37.75, 38.43 ±0.2 degrees two theta. (Figure 3)

The differential scanning calorimetric analysis shows a single peak of endotherm at 119.53°C (Fig. 21).

The thermogravimetric analysis reveals that it is an anhydrous product. (Fig. 22) and Karl Fischer titration results moisture content of 0.2 %.

Example 15:

1.15 gm of lamivudine and 1.34 gm of zidovudine were taken in mortar and pestle. The mixture was triturated for 5 minutes to make a homogeneous mixture. 10 - 12 drops of methanol added to the homogeneous mixture and the trituration was further continued for 20 minutes. The product obtained was further dried at 40⁰C in a vacuum drier for four hours. Yield: 2.49 gm

The analysis of the product (FTIR, powder X-ray diffraction, TGA, DSC, melting point) revealed that it is exactly the same as that of physical mixture obtained in example 14. Example 16:

5 gm of co-crystal product as obtained by practicing the process of example 1 to 13 was added to 20 ml of isopropanol and the slurry so obtained was further stirred at ambient temperature for an hour. The slurry was further filtered and the product was dried at 4O⁰C in vacuum drier for four hours. Yield: 4.8 gm

The melting point of the resultant material is 94 - 95°C.

Example 17:

5 gm of co-crystal product as obtained by practicing the process of example 1 to 13 was added to 20 ml of water and the slurry so obtained was further stirred at ambient temperature for an hour. The slurry was further filtered and the product was dried at 4O⁰C in a vacuum drier for four hours. Yield 4.5 gm

The melting point of resultant material is 94 - 95⁰C.

Example 18: Preparation of tablets containing Lamivudine co-crystals and comparison with the tablets made out of physical mixture of Lamivudine and Zidovudine: * Qty. varies based on Assay OAB and water content of Lamivuidne and Zidovudine ** Qty. to be adjusted based on Assay OAB and water content of Lamivuidne and

S. Ingredients Mg/Tablet

No. TRIAL I TRIAL I

INTRAGRANULAR

1. Lamivudine and Zidovudine Co- 336.38 _

Crystal*

2. Lamivudine (Form I)* - 150.00

3. Zidovudine USP* - 174.89

4. Lactose monohydrate NF** 231.82 243.61

(Pharmatose DCL 11)

5. Dibasic Calcium phosphate USP 29.625 29.625

(Di-Tab)

6. Sodium Starch Glycolate NF 56.25 56.25

(Primojel Type A)

7. Povidone USP (PVP K-30) 15.00 15.00

8. lsopropyl Alcohol USP^*** Qs Qs

EXTRAGRANULAR

9. Sodium Starch Glycolate NF 75.00 75.00

(Primojel Type A)

10. Magnesium stearate NF 5.625 5.625

Total Weight 750.00 750.00

Zidovudine to keep tablet weight constant

*** Used as solvent for granulation. Evaporates during processing.

Dry mix was prepared by sifting Lactose monohydrate, Dibasic calcium Phosphate dihydrate, Sodium starch Glycolate through 30# ASTM S.S. Sieve and mixing together with Lamivudine and Zidovudine Co-crystal (for trial I) or Lamivudine and Zidovudine (For trial II) sifted through 30# ASTM S.S. Sieve. The dry mix was further0 granulated using Povidine solution in isopropyl alcohol as binder. Dried the granulated mass in dryer at 45±5°C and dried granules were sifted through 20# ASTM S.S. Sieve. Oversize granules were milled and sifted through 20# ASTM S.S. Sieve. The granules were blended with extragranular sodium starch glycolate and lubricated with Mg stearate. Lubricated blend was compressed using 17.5 X 7.185 mm modified-capsule-shaped punches. Analysis of Tablets:

Claims

1. Co-crystal of lamivudine with zidovudine comprising one molecule each of lamivudine, zidovudine and water; having distinct X-ray diffraction peaks at 2Θ of 9.57, 11.45, 13.68, 15.57, 16.49, 18.35, 18.82, 20.45, 22.18, 22.78, 24.52,

24.99, 26.36, 26.55, 26.58 ± 0.2°.

2. The co-crystal as claimed in claim 1 having peak of endotherm at about 100⁰C in its differential scanning calorimetry profile.

3. The co-crystal as claimed in claim 1 showing sharp weight loss of 1.2 to 1.9% between the temperatures 80° and 100° in its thermogravimetric analysis.

4. The co-crystal as claimed in claim 1 having unit cell dimensions of

a = 8.6899 (10) A α = 90° b = 7.2501 (9) A β = 92.506° c = 18.504 (2) A _γ = 90°

5. A process for preparation of co-crystal of lamivudine with zidovudine comprising of trituration of equimolar quantities of Lamivudine and zidovudine in the presence of water at ambient temperature, with optional addition of organic solvent during trituration, and drying of the product.

6. The process as claimed in claim 5 wherein the organic solvent is selected from the group of ethanol, methanol, acetone, acetonitrile or mixtures thereof.

7. The process as claimed in claim 5 wherein the solid mixture obtained after trituration is added to the mixture of organic solvent and water, stirred at 55 - 65°C, allowing the solvents to evaporate slowly and seeded to obtain co- crystal.

8. The process as claimed in claim 7 wherein the organic solvent employed is selected from C1 to C4 aliphatic alcohols

9. The process as claimed in claim 8 wherein the organic solvent employed is ethanol.

10. A process for preparation of the co-crystal of lamivudine with zidovudine comprising stirring equimolar quantities of lamivudine and zidovudine in an organic solvent in the presence of water at ambient temperature, evaporation of solvents of the solution, allowing the product to get crystallized with optional seeding, isolation of the co-crystals and drying.

11. The process as claimed in claim 10 wherein the organic solvent employed is selected from methanol, ethanol, acetone, acetonitrile or mixtures thereof.

12.A pharmaceutical composition in solid dosage unit form comprising of a therapeutically effective amount of co-crystals of equimolar proportion of lamivudine, zidovudine and water in combination with a pharmaceutically acceptable carrier therefor.

13.A pharmaceutical composition according to claim 12 in oral administration form.

14. A pharmaceutical composition according to claim 13 in tablet form.

15. Use of therapeutically effective amount of co-crystal of equimolar proportions of Zidovudine, Lamivudine and water for the manufacture of medicament for treatment of HIV infections in humans.