Salt formation is a well-known technique to modify and optimize the physical chemical properties of an ionizable research or development compound. Properties such as solubility, dissolution rate, hygroscopicity, stability, impurity profiles, crystal habit can be influenced by using a variety of pharmaceutically acceptable counterions. Even polymorphism issues can be resolved in many cases by formation of salts. The crystal structure of a salt is usually completely different from the crystal structure of the conjugate base or acid and also differs from one salt to another. The modification of physical chemical properties, mainly solubility and dissolution rate, may also lead to changes in biological effects such as pharmacodynamics and pharmacokinetics, including bioavailability and toxicity profile. Owing to dramatic changes in the techniques applied in pharmaceutical discovery programs over the past 20 years, the physical chemical properties of development candidates have changed substantially. Drug design based on high-throughput screening has in general led to more lipophilic compounds exhibiting low aqueous solubility. There are many well-known formulation techniques to increase aqueous solubility, e.g., micronization, nanosizing, or complexation with cyclodextrins. The use of solid solutions and solid dispersions is another way to improve bioavailability for development candidates with low solubility. Nevertheless, formation of salts is almost the only chemical technique available to change aqueous solubility and dissolution rate without changing the API molecule. Further options for modifying these properties comprise the choice of the polymorphic form including solvates and formation of cocrystals.
A journal titled "Trends in Active Pharmaceutical Ingredient Salt selection based on Analysis of the Orange book Database" as published in J. Med. Chem. 2007,50, 6665-72 basically gives an insight to various salts reported of different API's. As per the journals, the two pie charts given below show the Overall distribution of anions & Cations used in API salt formation.

Succinate Phosphate Pamoate Nitrate Napsylate Methylsulfate
Acetate (17)
Besylate (4)
Bromide (24)
Chloride (279)
Citrate (14)
Fumarate (9)
Gluconate (2)
Iodide (5)
Iseth innate (2)
Lactate (7) i Malate (2)
Maieate (22)
Mesylate (22)
Methylsulfate (2)
Napsylate (2)
Nitrate (9)
Pamoate (4}
Phosphate (14)
Succinate (Q)
Sulfate (39)
Tartrate (20) l Tosylate (2)
Only used once (16)

Citrate Fumarale Gluconate Iodide lse1hionate/Malate Mesylate
Lactate Maieate

Anionic Salts

Piperazine Meglumine Magnesium _LysineDiethy|amine
Diethanolamine ""-Cholinate
Calcium
Benzathine Zinc Tromethamine
f Benzathine (1)
Calcium (12)
Cholinate (1)
Diethanolamine (1) i Diethylamine (1) i Lysine (1) i Magnesium (2)
Meglumine (5)
Piperazine(l)
Potassium (11)
Procaine (1) t Silver (1)
Sodium (131) i Tromethamine (3)
Zinc (2)

Silver Procaine
Potassium

Cationic Salts
Another journal, Titled "Polymorphs, Salts, and cocrystals: What's in a Name", as published in Cyst. Growth Des., 2012, 12, 214-2152, provides an insight in Food and Drug Administration (FDA) guidance concerning regulatory classification of pharmaceutical cocrystals of active pharmaceutical ingredients (APIs) addressed two matters of topical interest to the crystal engineering and pharmaceutical science communities: (1) a proposed definition of cocrystals; (2) a proposed classification of pharmaceutical cocrystals as dissociable "API-excipient" molecular complexes.
Another communication as published in CrystEngComm 2014, 16, 7393-7396, titled "Drug-drug salt forms of Ciprofloxacin with diflunisal and indoprofen". Provides drug-

drug salt form. In this journal two salt forms of a fluoroquinolone antibacterial drug, ciprofloxacin (CIP), with non-steroidal anti-inflammatory drugs, diflunisal (CIP/DIF) and indoprofen (CIP/INDP/H20), were synthesized and characterized by PXRD, FTIR, DSC, TGA and HSM. Crystal structure determination allowed us to study the drug-drug interactions and the piperazine-based synthon (protonated piperazine carboxylate) in the two forms, which is potentially useful for the crystal engineering of new salt forms of many piperazine based drugs.
PCT world patent application WO2005/023766 by Biocon, relates to a novel compound of formula which is basically a drug-drug salt form of Atorvastatin & metformin, wherein the compound is prodrug and releases two pharmaceutically active moieties, which has independent pharmacological activity and are used for treating hyperlipidemia and diabetes. Atorvastatin is generally administered as a calcium salt so that active open acid form is made available. Antihyperglycemic agents are used for treatment of diabetes. Metformin is used for treatment of Non- insulin dependent diabetes mellitus (NIDDM). Metformin is generally administered a HCI salt. The present inventions disclose a novel compound which can be used for simultaneous treatment of hyperlipidemia and diabetes.
Multicomponent pharmaceutical forms consisting of an active pharmaceutical ingredient (API) and an inactive co-former, which is ideally a generally recognized as safe (GRAS) substance, have been well explored in recent times. Formation of co-crystals and salt forms can improve an API's physicochemical properties, such as solubility and bioavailability, and the mechanical properties of individual drugs without changing any covalent bonds in either of the species. Due to the simple and convenient preparation methods, there is an increased interest in the discovery of multi-API forms as evident from the recent rise in the number of publications and patent applications. Examples of these multi-API forms include the crystalline forms of theophylline with phenobarbital, ethenzamide with gentisic acid, meloxicam with aspirin, acetylsalicylic acid with (L)-theanine, acetaminophen with theophylline, lamivudine with zidovudine,

sulfamethazine with theophylline, isoniazid with 4-aminosalicylic acid and pyrazinamide with isoniazid. Salt formation is the most widely practiced method to greatly improve the solubility and stability of drugs.
SUMMARY OF THE INVENTION

Montelukast-Sitagliptin Amine Salt - (MSA) - Structure 1
This patent application reports the synthesis of novel drug-drug amine salts & amide derivatives of various Acid drugs, mainly, Atorvastatin, Montelukast, Fexofenadine, Rosuvastatin, Simvastatin, Lovastatin, Ursodiol, Acefyllinate, Repeglinide, Furosemide, Telmisartan, Diclofenac, Ibuprofen, Indomethacin & Acetyl salicyclic acid and other carboxylic acid group containing drugs. The amine drug/API are selected from Desloratadine, Loratadine, Levocetirizine, Cetirizine, Sitagliptin, Saxagliptin, Linagliptin, Alogliptin, Vildagliptin, Acetaminophen, Olmesartan Medoxomil, Candesartan Cilexetil, Telmisartan, Valsartan, Irbesartan, Losartan, Azilsartan, Eprosartan, Fimasartan, Linezolid, Aripiperazole, Metformin, Doxofylline, Azacyclonol, Aliskiren, Famotidine, Metformin, Clopidogrel, Alizapride, Amlodipine & Voglibose and other drugs containing primary, secondary or tertiary amine groups . These enlisted amines are used for the formation of both amine salt as well as amide derivatives. The amide salt formation is accompanied by release of water molecule to form a new entity, which may have therapeutic activities of both APIs. For example Montelukast & Sitagliptin. The structure of one such drug-drug salt & amide derivative is as given below:


Montelukast-Sitagliptin Amide Derivative - (MSAD) - Structure 2
BRIEF DESCRIPTION OF THE FIGURES
A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawing of which:
Fig 1: XRD of Montelukast-Sitagliptin amine salt
Fig 2: XRD of Montelukast-Sitagliptin amide
DETAILED DESCRIPTION OF THE INVENTION
Numerous variations and additions to the various embodiments suggested herein will be apparent to those skilled in the art in light of the instant disclosure, which do not depart from the instant invention. Hence, the following specification is intended to illustrate some particular embodiments of the invention, and not to exhaustively specify all permutations, combinations and variations thereof.
The first embodiment of the present invention relates to the preparation of drug-drug salt form of an acid drug with an amine drug which comprises:

(a) To a solution or suspension of acid drug in an aromatic or aliphatic non-halogenated or halogenated hydrocarbon selected from benzene, toluene, xylenes, heptane, hexane, pentane, Methylene chloride, chloroform, carbon tetrachloride etc or an eliphatic ester such as ethyl acetate, Isopropyl acetate, Butyl acetate etc cyclic or acyclic ethers like Tetrahydrofuran, Methyl tert-butyl ether, Diisopropyl ether etc or aliphatic alcohols like Methanol, ethanol, propanol, butanol etc or a mixture thereof,
(b) Adding Amine drug with stirring
(c) Stirring of reaction mass for complete crystallization
(d) Isolating the resulting product by routine filtration as wet cake.
(e) Drying of the wet cake under vacuum at 40-60 °C to get desired drug-drug salt of two APIs
The second embodiment of the present invention relates to the preparation of drug-drug amide derivative of an acid drug with an amine drug which comprises:
(I) To a solution or suspension of acid drug in an aromatic or aliphatic non-
halogenated or halogenated hydrocarbon selected from benzene, toluene,
xylenes, heptane, hexane, pentane, Methylene chloride, chloroform, carbon
tetrachloride etc or an eliphatic ester such as ethyl acetate, Isopropyl acetate,
Butyl acetate etc cyclic or acyclic ethers like Tetrahydrofuran, Methyl tert-
butyl ether, Diisopropyl ether etc or aliphatic alcohols like Methanol,
ethanol, propanol, butanol etc or a mixture thereof, at 0-30°C.
(II) Adding slow addition of 1-Hydroxybenzotriazole, & N-(3-
Dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride .
(III) Stirring of reaction mass overnight preferably for 20-24 hrs at 20-40 C.
(IV) Isolating the product from organic layer after water washing by complete recovery of solvent.
(V) Purification of resulting product in Methylene chloride, chloroform, carbon tetrachloride etc or an eliphatic ester such as ethyl acetate, Isopropyl acetate, Butyl acetate etc cyclic or acyclic ethers like Tetrahydrofuran, Methyl tert-butyl ether, Diisopropyl ether etc or aliphatic alcohols like Methanol, ethanol, propanol, butanol with or without using water

(VI) Isolating the product as wet cake by routine filtration.
(VII) Drying of wet cake under vacuum at 40-60°C to get desired pure amide.
The Third embodiment of the present invention relates to the preparation of drug-drug amide derivative of an acid drug with an amine drug which comprises: (A). To a solution or suspension of acid drug in an aromatic or aliphatic non-halogenated or halogenated hydrocarbon selected from benzene, toluene, xylenes, heptane, hexane, pentane, Methylene chloride, chloroform, carbon tetrachloride etc or a mixture thereof.
(B). Adding thionyl chloride & stirring for 1-4 hrs. (C ). Adding amine drug to the resulting reaction mass with stirring. (D). Isolating the product from organic layer after water washing by complete recovery of solvent.
(E ). Purification of resulting product in Methylene chloride, chloroform, carbon tetrachloride etc or an eliphatic ester such as ethyl acetate, Isopropyl acetate, Butyl acetate etc cyclic or acyclic ethers like Tetrahydrofuran, Methyl tert-butyl ether, Diisopropyl ether etc or aliphatic alcohols like Methanol, ethanol, propanol, butanol with or without using water
(F ). Isolating the product as wet cake by routine filtration. (G). Drying of wet cake under vacuum at 40-60°C to get desired pure amide.
The Fourth embodiment of the present invention relates to the preparation of drug-drug amide derivative of an acid drug with an amine drug which comprises:
(a) To a solution or suspension of acid & amine drugs in cyclic or acyclic ethers
like Tetrahydrofuran, Methyl tert-butyl ether, Diisopropyl ether etc or aliphatic
alcohols like Methanol, ethanol, propanol, butanol.
(b). Adding inorganic acid in catalytic amount & refluxing of reaction mass .
(c). After reaction completion, Isolating the product from organic layer by complete
recovery of solvent.
(d). Purification of resulting product in Methylene chloride, chloroform, carbon
tetrachloride etc or an eliphatic ester such as ethyl acetate, Isopropyl acetate, Butyl

acetate etc cyclic or acyclic ethers like Tetrahydrofuran, Methyl tert-butyl ether,
Diisopropyl ether etc or aliphatic alcohols like Methanol, ethanol, propanol, butanol
with or without using water
(e). Isolating the product as wet cake by routine filtration.
(f). Drying of wet cake under vacuum at 40-60°C to get desired pure amide.
According to first aspect of the current embodiment, the acid drug used in step a) may be selected from Atorvastatin, Montelukast, Fexofenadine, Rosuvastatin, Simvastatin, Lovastatin, Ursodiol, Acefyllinate, Repeglinide, Furosemide, Telmisartan, Diclofenac, Ibuprofen, Indomethacin & Acetyl salicyclic acid and other carboxylic acid group containing drugs.
According to second aspect of current embodiment, the other amine drug used in step b) as base may be selected from Desloratadine, Loratadine, Levocetirizine, Cetirizine, Sitagliptin, Saxagliptin, Linagliptin, Alogliptin, Vildagliptin, Acetaminophen, Olmesartan Medoxomil, Candesartan Cilexetil, Telmisartan, Valsartan, Irbesartan, Losartan, Azilsartan, Eprosartan, Fimasartan, Linezolid, Aripiperazole, Metformin, Doxofylline, Azacyclonol, Aliskiren, Famotidine, Metformin, Clopidogrel, Alizapride & Voglibose other drugs containing primary, secondary or tertiary amine groups .
The invention is further illustrated by non-limiting examples. Thus the following examples should not construe the scope of the protection sought in this invention.
EXAMPLE-1
Preparation of Montelukast-Sitagliptin salt (MSA)
The Montelukast acid or l-[[[(li?)-l-[3-[(l£)-2-(7-Chloro-2-
quinolinyl)ethenyl]phenyl]-3-[2-(l-hydroxy-l-
methylethyl)phenyl]propyl]thio]methyl]cyclopropaneacetic acid (10 g) is dissolved in
toluene (70 ml) at 50-60°C under stirring. After complete dissolution of Montelukast
acid, Sitagliptin Base or 7-[(3i?)-3-Amino-l-oxo-4-(2,4,5-trifluorophenyl) butyl]-
5,6,7,8-tetrahydro-3-(trifluoromethyl)-l,2,4-triazolo[4,3-a]pyrazine ( 7g) is added to it.

The reaction mass is stirred at 40-50°C for 15-30 minutes. The reaction mass is then allowed to attain ambient temperature and stirred for 10-20 hrs. The product is filtered off to get the desired Montelukast-Sitagliptin amine (MSA) salt. The salt is dried under vacuum at 50-60°C to get the desired product. (Yield = 15 g)
EXAMPLE-2 Preparation of Montelukast-Desloratadine salt
The Montelukast acid or l-[[[(li?)-l-[3-[(l£)-2-(7-Chloro-2-
quinolinyl)ethenyl]phenyl]-3-[2-(l-hydroxy-l-
methylethyl)phenyl]propyl]thio]methyl]cyclopropaneacetic acid (10 g) is dissolved in toluene (70 ml) at 50-60°C under stirring. After complete dissolution of Montelukast acid, Desloratadine (6 g) is added to it. The reaction mass is stirred at 40-50°C for 15-30 minutes. The reaction mass is then allowed to attain ambient temperature and stirred for 10-20 hrs. The product is filtered off to get the desired Montelukast-Desloratadine salt. The salt is dried under vacuum at 50-60°C to get the desired product. (Yield = 12 g)
EXAMPLE-3
Preparation of Montelukast-Levocetrizine salt
The Montelukast acid or l-[[[(li?)-l-[3-[(l£)-2-(7-Chloro-2-
quinolinyl)ethenyl]phenyl]-3-[2-(l-hydroxy-l-
methylethyl)phenyl]propyl]thio]methyl]cyclopropaneacetic acid (10 g) is dissolved in toluene (70 ml) at 50-60°C under stirring. After complete dissolution of Montelukast acid, Levocetirizine (7 g) is added to it. The reaction mass is stirred at 40-50°C for 15-30 minutes. The reaction mass is then allowed to attain ambient temperature and stirred for 10-20 hrs. The product is filtered off to get the desired Montelukast-Levocetirizine salt. The salt is dried under vacuum at 50-60°C to get the desired product. (Yield = 14 g)
EXAMPLE-4
Preparation of Montelukast-Cetrizine salt

The Montelukast acid or l-[[[(li?)-l-[3-[(l£)-2-(7-Chloro-2-
quinolinyl)ethenyl]phenyl]-3-[2-(l-hydroxy-l-
methylethyl)phenyl]propyl]thio]methyl]cyclopropaneacetic acid (10 g) is dissolved in toluene (70 ml) at 50-60°C under stirring. After complete dissolution of Montelukast acid, Cetirizine (7 g) is added to it. The reaction mass is stirred at 40-50°C for 15-30 minutes. The reaction mass is then allowed to attain ambient temperature and stirred for 10-20 hrs. The product is filtered off to get the desired Montelukast-Cetirizine salt. The salt is dried under vacuum at 50-60°C to get the desired product. (Yield = 14 g)
EXAMPLE-5
Preparation of Montelukast-Loratadine salt
The Montelukast acid or l-[[[(li?)-l-[3-[(l£)-2-(7-Chloro-2-
quinolinyl)ethenyl]phenyl]-3-[2-(l-hydroxy-l-
methylethyl)phenyl]propyl]thio]methyl]cyclopropaneacetic acid (10 g) is dissolved in toluene (70 ml) at 50-60°C under stirring. After complete dissolution of Montelukast acid, Loratadine (7 g) is added to it. The reaction mass is stirred at 40-50°C for 15-30 minutes. The reaction mass is then allowed to attain ambient temperature and stirred for 10-20 hrs. The product is filtered off to get the desired Montelukast-Loratadine salt. The salt is dried under vacuum at 50-60°C to get the desired product. (Yield = 14 g)
EXAMPLE-6 Preparation of Montelukast-Sitagliptin amide (MS AD)
The Montelukast acid (lOg) and Sitagliptin base (7g) are dissolved in methylene
chloride (100 ml) followed by cooling of reaction mass to 0-10°C and 1-
Hydroxybenzotriazole (7 g), & N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide
hydrochloride (10 g) are added at 0-10°C. Then the temperature of reaction mass is
raised to 25-35 °C and stirred for 20-24 hours. After completion of reaction, the reaction mass is quenched by addition of water (100 ml). After layer separation, the organic layer containing product is distilled under vacuum to give Montelukast-Sitagliptin

amide (MSAD) which purified by recrystallization using aqueous methanol and the desired purified MSAD is isolated as wet cake by filtration followed by its drying under vacuum at 40-60°C to give final pure Montelukast-Sitagliptin amide (MSAD). (Yield = 17g)
EXAMPLE-7 Preparation of Montelukast-Desloratadine amide
The Montelukast acid (lOg) and Desloratadine (7g) are dissolved in methylene chloride (100 ml) followed by cooling of reaction mass to 0-10°C and 1-Hydroxybenzotriazole (7 g), & N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (10 g) are added at 0-10°C. Then the temperature of reaction mass is raised to 25-35 °C and stirred for 20-24 hours. After completion of reaction, the reaction mass is quenched by addition of water (100 ml). After layer separation, the organic layer containing product is distilled under vacuum to give Montelukast-Desloratadine amide which purified by recrystallization using aqueous methanol and the desired purified MSAD is isolated as wet cake by filtration followed by its drying under vacuum at 40-60°C to give final pure Montelukast- Desloratadine amide (MSAD). (Yield = 15g)
EXAMPLE-8
Preparation of Montelukast-Saxagliptin amide
The Montelukast acid (lOg) and Saxagliptin (6g) are dissolved in methylene chloride (100 ml) followed by cooling of reaction mass to 0-10°C and 1-Hydroxybenzotriazole (7 g), & N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (10 g) are added at 0-10°C. Then the temperature of reaction mass is raised to 25-35 °C and stirred for 20-24 hours. After completion of reaction, the reaction mass is quenched by addition of water (100 ml). After layer separation, the organic layer containing product is distilled under vacuum to give Montelukast- Saxagliptin amide which purified by recrystallization using aqueous methanol and the desired purified MSAD is isolated as wet cake by filtration followed by its drying under vacuum at 40-60°C to give final pure Montelukast- Saxagliptin amide . (Yield = 15g)

EXAMPLE-9
Preparation of Montelukast-Linagliptin amide
The Montelukast acid (lOg) and Linagliptin (6g) are dissolved in methylene chloride (100 ml) followed by cooling of reaction mass to 0-10°C and 1-Hydroxybenzotriazole (7 g), & N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (10 g) are added at 0-10°C. Then the temperature of reaction mass is raised to 25-35 °C and stirred for 20-24 hours. After completion of reaction, the reaction mass is quenched by addition of water (100 ml). After layer separation, the organic layer containing product is distilled under vacuum to give Montelukast- Linagliptin amide which purified by recrystallization using aqueous methanol and the desired purified MSAD is isolated as wet cake by filtration followed by its drying under vacuum at 40-60°C to give final pure Montelukast- Linagliptin amide . (Yield = 15g)
EXAMPLE-10
Preparation of Montelukast-Levocetirizine amide
The Montelukast acid (lOg) and Levocetirizine (6g) are dissolved in methylene chloride (100 ml) followed by cooling of reaction mass to 0-10°C and 1-Hydroxybenzotriazole (7 g), & N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (10 g) are added at 0-10°C. Then the temperature of reaction mass is raised to 25-35 °C and stirred for 20-24 hours. After completion of reaction, the reaction mass is quenched by addition of water (100 ml). After layer separation, the organic layer containing product is distilled under vacuum to give Montelukast- Levocetirizine amide which purified by recrystallization using aqueous methanol and the desired purified MSAD is isolated as wet cake by filtration followed by its drying under vacuum at 40-60°C to give final pure Montelukast Levocetirizine amide . (Yield = 15g)
EXAMPLE-11
Preparation of Montelukast-Sitagliptin amide (MSAD)

The Montelukast acid (lOg) is dissolved in methylene chloride (100 ml) followed by cooling of reaction mass to 0-10 °C and Thionyl chloride (20ml) is added to it . After stirring for 1-4 hrs, Sitagliptin base (7g) is added to it. Then the temperature of reaction mass is raised to 25-35 °C and stirred for 20-24 hours. After completion of reaction, the reaction mass is quenched by addition of water (100 ml). After layer separation, the organic layer containing product is distilled under vacuum to give Montelukast-Sitagliptin amide (MSAD) which purified by recrystallization using aqueous methanol and the desired purified MSAD is isolated as wet cake by filtration followed by its drying under vacuum at 40-60°C to give final pure Montelukast-Sitagliptin amide (MSAD). (Yield = 15g).
EXAMPLE-12
Preparation of Montelukast-Sitagliptin amide (MSAD)
The Montelukast acid (lOg) and Sitagliptin base (7g) are dissolved in Methanol (70 ml) followed by cooling of reaction mass to 0-10 °C and sulphuric acid (1ml) is added to it slowly and reaction mass is refluxed for 15-20 hours. After completion of reaction, the reaction mass is quenched by addition of water (50ml) followed by complete recovery of solvent. The resulting residue is purified by recrystallization using aqueous methanol and the desired purified MSAD is isolated as wet cake by filtration followed by its drying under vacuum at 40-60°C to give final pure Montelukast-Sitagliptin amide (MSAD). (Yield = 16g).

WE CLAIM:

1.A Novel drug-drug salts of acid drugs & amine drugs, wherein the acid drugs and its conjugate amine drugs are therapeutically active individually.
2. The acid drug as claimed in claim 1 wherein the acid drug is be selected from Atorvastatin, Montelukast, Fexofenadine, Rosuvastatin, Simvastatin, Lovastatin, Ursodiol, Acefyllinate, Repeglinide, Furosemide, Telmisartan, Valsartan, Diclofenac, Ibuprofen, Indomethacin, Aceclofenac, Candesartan, Sacubitril, Valsartan, Chenodeoxycholic acid (CDCA), 7-Ketolithocholic Acid (KLCA), Apixaban acid, Tranexamic acid, Ambrisentan, Indomethacin, Ketorolac, Etodolac, Diacerin, Acebrophylline & Acetyl salicyclic acid and other drugs containing carboxylic acid group which are all therapeutically active & a mixture thereof.
3. The conjugate amine drug as claimed in claim 1 wherein the amine drug is be selected from Desloratadine, Loratadine, Levocetirizine, Cetirizine, Sitagliptin, Saxaghptin, Linaghptin, Alogliptin, Vildaghptin, Acetaminophen, Olmesartan Medoxomil, Candesartan Cilexetil, Telmisartan, Valsartan, Irbesartan, Losartan, Azilsartan, Eprosartan, Fimasartan, Linezolid, Aripiperazole, Metformin, Doxofylline, Azacyclonol, Aliskiren, Famotidine, Metformin, Clopidogrel, Alizapride, Amlodipine, Voglibose or 4-{4-[(5S)-5-(Aminomethyl)-2-oxo-l,3-oxazolidin-3-yl]phenyl} morpholin-3-one and other drugs containing amine group which are all therapeutically active & a mixture thereof.
4. The novel drug-drug amide compounds of acid drugs and amine drugs as claimed in claim 2 and in claim 3 and pharmaceutical compositions thereof.
5. The novel process of preparation of drug-drug salt as claimed in claim 1 wherein the method comprises:

a) Dissolving any acid drug of claim 2, in an aromatic or aliphatic non-halogenated or halogenated hydrocarbon selected from benzene, toluene, xylenes, heptane, hexane, pentane, Methylene chloride, chloroform, carbon tetrachloride or an aliphatic ester such as ethyl acetate, Isopropyl acetate, Butyl acetate or cyclic or acyclic ethers like Tetrahydrofuran, Methyl tert-butyl ether, Diisopropyl ether or aliphatic alcohols like Methanol, ethanol, propanol, butanol etc or a mixture thereof at 35-60°C.
b) Addition of amine drug of claim 3, with stirring at 35-60 °C.
c) Stirring the reaction mass at 40-50 °C for 15-30 minutes till the product is crystallized
d) Isolating the desired drug-drug salt product, as wet cake by filtration
e) Drying of wet cake under vacuum at 50-60°C till constant weight is obtained.

6. The novel montelukast-sitagliptin salt, Montelukast-Desloratadine salt, Montelukast-Levocetirizine salt, Montelukast-cetirizine salt, Montelukast-Loratadine salt prepared as per the method as claimed in claim 5 and pharmaceutical compositions thereof.
7. The novel process for the preparation of drug-drug amide derivatives as claimed in claim 4, wherein the method comprises:
a) Dissolving any acid drug of claim 2, in an aromatic or aliphatic non-halogenated or halogenated hydrocarbon selected from benzene, toluene, xylenes, heptane, hexane, pentane, Methylene chloride, chloroform, carbon tetrachloride or an aliphatic ester such as ethyl acetate, Isopropyl acetate, Butyl acetate or cyclic or acyclic ethers like Tetrahydrofuran, Methyl tert-butyl ether, Diisopropyl ether or aliphatic alcohols like Methanol, ethanol, propanol, butanol etc or a mixture thereof at 0-30°C.

b) Slow addition of any amine drug of claim 3, 1-Hydroxybenzotriazole
(HOBT), &N-(3-Dimethyl aminopropyl)-N'-ethylcarbodiimide (EDAC)
c) Stirring of reaction mass at 20-40°C for 20-24 hours.
d) Performing complete recovery of solvent from reaction mass under vacuum to get crude product
e) Purification of crude product of step d) above by recrystallizing it in
halogenated or non-halogenated hydrocarbon, selected from Methylene chloride,
chloroform, carbon tetrachloride or an aliphatic ester, selected from ethyl acetate,
Isopropyl acetate, Butyl acetate or cyclic or acyclic ethers, selected from
Tetrahydrofuran, Methyl tert-butyl ether, Diisopropyl ether or aliphatic alcohols,
selected from Methanol, ethanol, propanol, butanol with or without using water.
f) Isolating the desired drug-drug amide derivative, as wet cake by filtration
g) Drying of wet cake under vacuum at 40-60°C till constant weight is obtained. 8. The novel process for the preparation of drug-drug amide derivative as claimed in claim 4, wherein the method comprises:

a) Dissolving any acid drug of claim 2, in an aromatic or aliphatic non-halogenated or halogenated hydrocarbon selected from benzene, toluene, xylenes, heptane, hexane, pentane, Methylene chloride, chloroform, carbon tetrachloride or mixture thereof at 0-10°C.
b) Adding thionyl chloride to the solution prepared in a) above & stirring for 1-4 hours at 0-10 °C.
c) Adding any amine drug of claim 3, and allowed the reaction mass to attain ambient temperature
d) Stirring of reaction mass at 25-35 °C for 20-24 hours.

e) After completion of reaction, quenching of reaction mass by addition of water followed by its layer separation.
f) Performing complete recovery of solvent from separated organic layer under vacuum to get crude product
g) Purification of crude product of step d) above by recrystallizing it in
halogenated or non-halogenated hydrocarbon, selected from Methylene chloride,
chloroform, carbon tetrachloride or an aliphatic ester, selected from ethyl acetate,
Isopropyl acetate, Butyl acetate or cyclic or acyclic ethers, selected from
Tetrahydrofuran, Methyl tert-butyl ether, Diisopropyl ether or aliphatic alcohols,
selected from Methanol, ethanol, propanol, butanol with or without using water
h) Isolating the desired drug-drug amide derivative, as wet cake by filtration i) Drying of wet cake under vacuum at 40-60°C till constant weight is obtained.
9. The novel process for the preparation of drug-drug amide derivative as claimed in claim 4, which comprises
a) Dissolving any acid drug of claim 2 & any amine drug of claim 3, in cyclic or acyclic ethers like Tetrahydrofuran, Methyl tert-butyl ether, Diisopropyl ether or aliphatic alcohols like Methanol, ethanol, propanol, butanol etc or a mixture thereof at 0-10°C.
b) Adding catalytic quantity of an inorganic acid and refluxing the reaction mass for 15-20 hours till reaction completion
c) Performing complete recovery of solvent from reaction mass under vacuum to get crude product

d) Purification of crude product of step c) above by recrystallizing it in
halogenated or non-halogenated hydrocarbon, selected from Methylene chloride,
chloroform, carbon tetrachloride or an aliphatic ester, selected from ethyl acetate,
Isopropyl acetate, Butyl acetate or cyclic or acyclic ethers, selected from
Tetrahydrofuran, Methyl tert-butyl ether, Diisopropyl ether or aliphatic alcohols,
selected from Methanol, ethanol, propanol, butanol with or without using water
e) Isolating the desired drug-drug amide derivative, as wet cake by filtration
f) Drying of wet cake under vacuum at 40-60°C till constant weight is obtained. 10. The novel Montelukast-Sitagliptin, Montelukast-Desloratadine, Montelukast-Saxagliptin, Montelukast-Linaghptin, Montelukast-Levocetirizine amide derivatives prepared as per process as claimed in claim 7, 8 or 9 and pharmaceutical compositions thereof.