Preparation and Solid State Characterization of Paclitaxel Cocrystals

 

Muddukrishna B.S.¹ Krishnamurthy Bhat¹* and Gautham G. Shenoy²

¹Department of Pharmaceutical Quality Assurance, Manipal College of Pharmaceutical Sciences, Manipal University, Manipal, Karnataka, India

²Department of Pharmaceutical Chemistry, Manipal College of Pharmaceutical Sciences, Manipal University, Manipal, Karnataka, India

 

ABSTRACT:

Objective of the present study is to prepare a co crystal of paclitaxel with improved solubility and bio availability.

Paclitaxel is poorly water soluble and low bioavailable drug, this low oral bioavailability is mainly due to poor aqueous solubility and by the high affinity of paclitaxel for P-gp This research work foresees the advantages of co-crystal technology towards the enhancement of paclitaxel solubility and there by its bioavailability. Two sets of coformers were selected based on their chemical nature, using suitable cocrystal preparation techniques various batches of paclitaxel cocrystals were prepared and subjected to solid state characterization to determine the crystal structure of the cocrystals, as this can provide significant new insights into how the drug and coformer interact, and thereby provide an excellent crystal engineering guide to new cocrystals, potentially with improved properties. Instruments like Fourier transform infrared spectroscopy(FTIR), differential scanning calorimetry, X-ray powder diffraction will be used to determine their stability, and any phase transformations (including decomposition) which they might undergo as  a function of temperature. Principle involved in the formation of cocrystal is hydrogen bonding between C=O and N-H group of drug and COOH groups of coformers, which is confirmed by FTIR data and DSC experiments were carried out to study the melting point and heat of enthalpy of the cocrystals. Results clearly shows that the melting point of the cocrystals were increased which confirms the formation of cocrystals.  The drug and formation of cocrystals are explained by the X-ray powder diffraction patterns. The PXRD patterns of pure drug showed sharp well defined peaks(spectrum attached) and cocrystals PXRD patterns shows that there is a significant differences in the entire diffraction pattern,  changes in peak locations with respect to pure drug indicates change in arrangement of molecules, hence conforms the development of new crystalline phase.

 

 

 

INTRODUCTION:

Oral treatment with anticancer agents is, if feasible, to be preferred, as this route of administration is convenient to patients, reduces administration costs and facilitates the use of more chronic treatment regimens. Paclitaxel has become an established drug in the treatment of various human malignancies in current clinical practice. The drug is administered as I.V. infusion because of its poor bioavailability. However, I.V. administration is associated with a number of major drawback including severe hypersensitivity reactions, lethargy and hypotension.

 

Thus, much research is being carried out to identify alternative to intravenous formulations. Oral administration of paclitaxel is very attractive because it improves patients’ quality of life compliance.

 

Unfortunately paclitaxel has a very low oral bioavailability at less than 10% because of limited aqueous solubility, affinity for the CYP metabolic enzymes and the P-glycoprotein (Helen A. Bardelmeijer et al. 2000). Several strategies were attempted for the improvement of the oral bioavailability of paclitaxel like selective modulation of P-glycoprotein, self-emulsifying drug delivery systems and paclitaxel loaded lipid nano capsules(Sandra peltier et al. 2006). Cocrystals increase the diversity of solid-state forms of a drug even for non-ionizable drugs, and enhance pharmaceutical properties by modification of chemical stability, moisture uptake, mechanical behavior, solubility, dissolution rate, and bioavailability (Childs, Chyall et al. 2004; Rodríguez-Spong, Price et al. 2004; Trask, Motherwell et al. 2005).

 

If cocrystals are going to be a viable alternative for solid state forms of a drug bioavailability studies need to be performed. A recently published paper has reported that a 1:1 co crystal of 2-[4-(4-chloro-2-fluorophenoxy)phenyl] pyrimidine-4-carboxamide with glutaric acid that had a dissolution rate of 18 times higher than the pure drug and plasma concentration of three times for the same dose in dogs (McNamara, Childs et al. 2006).

 

While co-crystals provide an enhancement in the physicochemical properties of the drug and also a significant number of biologically nontoxic co-crystallizing molecules are available which enhances the bioavailability either by increasing the solubility and/ by inhibiting the metabolic enzymes (Georges houin et al. 2004), but not much work is carried out using this technology. These crystal engineering can also be carried out as solvent free technology which readily addresses the regulatory demand of quality by design and offers high potential for pharmaceuticals. Cocrystals are gaining much interest because the resulting new crystal forms of drugs many a times have different pharmaceutical, physical, and chemical properties compared to the original drug.

 

Figure: 1 (Chemical structure of Paclitaxel)

 

MATERIALS AND METHODS:

Drug: Paclitaxel as gift sample from Cipla, Mumbai and Intas, Mumbai.

Coforms:

Benzoic acid, malonic acid, Nicotinamide, Oxalic acid, Succinic acid, Tartaric acid

Instruments used: Differential Scanning calorimeter (Shimadzu), FTIR, PXRD, Incubator shaker.

 

Methods:

Selection of coformers:

The selection of relevant cocrystal former becomes a crucial issue and requires creating supramolecular libraries of crystallizing agents. Analysis of existing crystal structures represents the first step in a crystal engineering experiment and thereby collecting the information concerning common functional groups and how they engage in molecular association.

A search of the Cambridge Structural Database will be employed to identify likely hydrogen-bonding motifs for paclitaxel. Synthesis of new co-crystal materials will be guided by the outputs of this work. Based on the findings two sets of coformers were selected for the preparation of paclitaxel co crystals i.e. Set-1: Benzoic acid, malonic acid, Nicotinamide, Oxalic acid, Succinic acid, Tartaric acid. Set-2: DL-2 Amino-N-Butyric acid, DL- Aspartic acid, L-Glutamic acid, Proline and Tyrosine.

 

Preparation of cocrystals:

The ultimate goal of cocrystals design is to discover a solid form of paclitaxel with improved solubility, dissolution rate and bioavailability; Major techniques to generate cocrystals are solution based techniques (Slow solvent evaporation, slurry conversion and precipitation or anti solvent addition) and solid based techniques (Cogrinding & solvent assisted grinding). Solid based techniques were used to prepare the cocrystals. Totally 24 batches of cocrystals were prepared using two different solid based techniques and two different set of ratios.

 

Table: 1 Batches of paclitaxel cocrystals prepared using co grinding method

Sl. No.	Co Crystal Batch Code	Co former Used	Technique used	Ratio
1.	CCBA-1	Benzoic acid	Co grinding	1:1
2.	CCMA-1	Malonic acid	Co grinding	1:1
3.	CCNA-1	Nicotinamide	Co grinding	1:1
4.	CCOA-1	Oxalic acid	Co grinding	1:1
5.	CCSA-1	Succinic acid	Co grinding	1:1
6.	CCTA-1	Tartaric acid	Co grinding	1:1
7.	CCBA2	Benzoic acid	Co grinding	1:2
8.	CCMA-2	Malonic acid	Co grinding	1:2
9.	CCNA-2	Nicotinamide	Co grinding	1:2
10.	CCOA-2	Oxalic acid	Co grinding	1:2
1.1	CCSA-2	Succinic acid	Co grinding	1:2
12.	CCTA-2	Tartaric acid	Co grinding	1:2

 

Table: 2 Batches of paclitaxel cocrystals prepared using co grinding method

Sl. No.	Co Crystal Batch Code	Co former Used	Technique used	Ratio
13.	CCBA-3	Benzoic acid	S.A. Co grinding	1:1
14.	CCMA-3	Malonic acid	S.A. Co grinding	1:1
15.	CCNA-3	Nicotinamide	S.A.Co grinding	1:1
16.	CCOA-3	Oxalic acid	S.A. Co grinding	1:1
17.	CCSA-3	Succinic acid	S.A. Co grinding	1:1
18.	CCTA-3	Tartaric acid	S.A. Co grinding	1:1
19.	CCBA-4	Benzoic acid	S.A. Co grinding	1:2
20.	CCMA4	Malonic acid	S.A. Co grinding	1:2
21.	CCNA-4	Nicotinamide	S.A.Co grinding	1:2
22.	CCOA-4	Oxalic acid	S.A.Co grinding	1:2
23.	CCSA-4	Succinic acid	S.A.Co grinding	1:2
24.	CCTA-4	Tartaric acid	S.A. Co grinding	1:2

RESULTS AND DISCUSSION:

The prepared co-crystals were subjected to various characterization techniques like FTIR, DSC and PXRD and results are shown in the tables 3 to 5. Co crystals of paclitaxel with the batch no. CCTA-1, CCSA-1 & CCNA-1 prepared by cogrinding technique with the ratio 1:1 shows promising results. Principle involved in the formation of cocrystals is hydrogen bonding between C=O and N-H group of drug and COOH groups of coformers, which is confirmed by FTIR data and DSC experiments were carried out to study the melting point and heat of enthalpy of the cocrystals.

 

Results clearly shows that the melting point of the cocrystals were increased which confirms the formation of cocrystals.  The drug and formation of cocrystals are explained by the X-ray powder diffraction patterns.

 

The PXRD patterns of pure drug showed sharp well defined peaks(spectrum attached) and cocrystals PXRD patterns shows that there is a significant differences in the entire diffraction pattern,  changes in peak locations with respect to pure drug indicates change in arrangement of molecules, hence conforms the development of new crystalline phase.

 

 

Table 3. Major IR peaks (Wave numbers) of coformers

Co-formers	Major peaks  (Wave numbers, cm-1)	Melting points	Literature value
Succinic acid	3032.8, 2929.9, 1691.6, 1417.7, 1309.7, 1201.7, 916.22, 636.53.	182-184° C	181-184° C
Tartaric acid	3410.7, 3022.55, 2640.6, 1741.8, 1456.3, 1398.4, 1228.6, 891.1, 680.9.	172-174° C	171-174° C
Malonic acid	3354.3, 2945.4, 2362.9, 1730.3, 1431.2, 1217.1, 920.1, 653.9	135-137° C	133-137° C
Nicotinamide	3363.9, 3161.4, 3064.9, 2781.4, 2359.1, 1685.8, 1396.5, 613.4	128-130° C	128-130° C
Oxalic acid	3470.1, 2922.2, 2360.9, 1691.6, 1251.8, 1126.5, 721.4.	100-102° C	100-102° C
Benzoic acid	3064.9, 2837.4, 2559.6, 2359.1, 1687.8, 1290.4, 705.9	122-124° C	121-124° C

 

Table 4. Major IR peaks (wavenumbers) and DSC thermogram results of cocrystals

Samples	Composition	Major peaks (Wave numbers, cm-1) (By FTIR)	Melting points (By DSC)
Paclitaxel + Succinic acid	1:1	3057.3(N-H), 2929.9, 1689.7,(C=O) 1415.8, 1311.6, 1201.7, 916.22, 636.53.	204.0° C
Paclitaxel+Tartaric acid	1:1	3499.0(N-H), 3061.1, 2638.7, 2360.9, 1745.6(C=O), 1541.2, 1398.4, 1282.7, 895.1, 705.9.	216.3° C
Paclitaxel +Malonic acid	1:1	3464.3, 2945.4, 2360.9, 1735.9, 1429.3, 1219.1, 912.4, 653.9	140.0° C
Paclitaxel +Nicotinamide	1:1	3504.7(N-H),, 3365.9, 3063.1, 2781.4, 2360.9, 1735.9,(C=O), 1396.5, 705.9, 611.4.	138.0° C
Paclitaxel +Oxalic acid	1:1	3502.8, 2968.5, 2360.9, 1734.1, 1246.1, 1070.5, 709.8.	110.0° C
Paclitaxel +Benzoic acid	1:1	3504.7, 2835.4, 2559.6, 2364.8, 1653.1, 1290.4, 707.9	125.0° C

 

Table 5. PXRD data of cocrystals and paclitaxel

SAMPLE	2θ (deg)	d (ang.)	Intensity
Paclitaxel	12.22	7.23	2487.74
Paclitaxel:Tartaric acid(1:1) Co-crystal	19.1674	4.62672	4502.48
Paclitaxel:Succinic acid(1:1) Co-crystal	25.82	3.44775	1083.47
Paclitaxel:Nicotinamide(1:1) Co-crystal	14.5008	6.10348	962.23

 

Fig 1: PXRD of Paclitaxel

 

Fig 2: PXRD of Paclitaxel:Tartaric acid(:1) Co-crystal

 

Fig 3: PXRD of Paclitaxel:Succinic acid(1:1) Co-crystal

 

Fig 4: PXRD of Paclitaxel:Nicotinamide(1:1) Co-crystal

 

Fig 5: FTIR Spectrum of Paclitaxel

 

Fig 6: FTIR Spectrum of Paclitaxel:Tartaric acid(1:1) Co-crystal

 

Fig 7: FTIR Spectrum of Paclitaxel:Succinic acid(1:1) Co-crystal

 

Fig 8: FTIR Spectrum of Paclitaxel:Nicotinamide(1:1) Co-crystal

 

Fig 9: DSC thermogram of Paclitaxel

 

Fig 10: DSC thermogram of Paclitaxel:Tartaric acid(1:1) Co-crystal

 

Fig 11: DSC thermogram of Paclitaxel:Succinic acid(1:1) Co-crystal

 

Fig 12: DSC thermogram of Paclitaxel:Nicotinamide(1:1) Co-crystal

 

CONCLUSION:

Results clearly shows that paclitaxel cocrystals prepared from tartaric acid(CCTA-1), succinic acid(CCSA-1) and nicotinamide(CCNA-1) by cogrinding technique in the ratio of 1:1 exhibits the formation of cocrystals and it is confirmed by the solid state characterization.

 

FTIR data and DSC experiments clearly shows that the melting point of these cocrystals were increased which confirms the formation of cocrystals. The PXRD patterns of cocrystals shows a significant differences in the diffraction pattern,  changes in peak locations with respect to pure drug indicating change in arrangement of molecules, hence conforms the development of new crystalline phase.

 

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Received on 10.01.2014       Modified on 21.01.2014

Accepted on 25.01.2014      © RJPT All right reserved