Improvement of Physicochemical and Solubility of Dipyridamole by Cocrystallization Technology

Abstract

The aim of this study was to develop a pH-independent release formulation of dipyridamole (DP) by the combined use of pH-modifier technology and cocrystal technology tartaric acid (TA) was selected as an appropriate pH-modifier in terms of improving physicochemical properties and dissolution behavior of DP under neutral conditions. Molecular docking method was used to identify the suitable conformer. Upon optimization of the ratio of TA to DP (molar ratio of 1:1, 1:2 and 1:3) was prepared by a solvent assisted griding method. Scanning electron microscopy images revealed that formation of DP-TA co crystals supported by supported by powder X-ray diffraction and differential scanning calorimetry analyses. Spectroscopic analysis suggested that there might be inter-molecular interaction among DP and TA resulting in pH independent dissolution behavior of drug substance. The study confirmed the selection of proper coformer and exhibited enhanced physicochemical, solubility and stability of the Dipyridamole cocrystals. Hence, based upon results it revealed that cocrystallization helps in improving the physicochemical properties of the API. Keywords: Dipyridamole, Coformer, Molecular docking, Radar chart, solvent assisted griding, Cocrystals

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Gawade et al Journal of Drug Delivery & Therapeutics. 2021; 11(1-s):43-48
ISSN: 2250-1177 [43] CODEN (USA): JDDTAO
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Open Access Full Text Article Research Article
Improvement of Physicochemical and Solubility of Dipyridamole by
Cocrystallization Technology
Gawade Ashwini1*, Kuchekar Ashwin1, Boldhane Sanjay2, Baheti Akshay1
1 School of Pharmacy, Dr. Vishwanath Karad, MIT WPU, Paud Road, Kothrud, Pune 411 038
2 Sr. General Manager -Formulation Development at Micro Labs Ltd., Bangalore 560 001
Article Info:
_________________________________________
Article History:
Received 08 Dec 2020;
Review Completed 21 Jan 2021
Accepted 30 Jan 2021;
Available online 15 Feb 2021
_________________________________________
Cite this article as:
Gawade A, Kuchekar A, Boldhane S, Baheti A,
Improvement of Physicochemical and Solubility of
Dipyridamole by Cocrystallization Technology,
Journal of Drug Delivery and Therapeutics. 2021;
11(1-s):43-48
DOI:http://dx.doi.org/10.22270/jddt.v11i1-s.4696
Abstract
______________________________________________________________________________________________________
The aim of this study was to develop a pH-independent release formulation of dipyridamole
(DP) by the combined use of pH-modifier technology and cocrystal technology tartaric acid
(TA) was selected as an appropriate pH-modifier in terms of improving physicochemical
properties and dissolution behavior of DP under neutral conditions. Molecular docking
method was used to identify the suitable conformer. Upon optimization of the ratio of TA to
DP (molar ratio of 1:1, 1:2 and 1:3) was prepared by a solvent assisted griding method.
Scanning electron microscopy images revealed that formation of DP-TA co crystals supported
by supported by powder X-ray diffraction and differential scanning calorimetry analyses.
Spectroscopic analysis suggested that there might be inter-molecular interaction among DP
and TA resulting in pH independent dissolution behavior of drug substance. The study
confirmed the selection of proper coformer and exhibited enhanced physicochemical,
solubility and stability of the Dipyridamole cocrystals. Hence, based upon results it revealed
that cocrystallization helps in improving the physicochemical properties of the API.
Keywords: Dipyridamole, Coformer, Molecular docking, Radar chart, solvent assisted
griding, Cocrystals
*Address for Correspondence: Dr. Ashwini Gawade, School of Pharmacy, Dr. Vishwanath Karad, MIT WPU, Paud Road, Kothrud, Pune 411 038
INTRODUCTION
Dipyridamole USP is a platelet inhibitor chemically
described as 2,2',2",2"'-[(4,8- Dipiperidinopyrimido[5,4-
d]pyrimidine-2,6-diyl)dinitrilo]-tetraethanol.
Dipyridamole is an odorless yellow crystalline powder,
having a bitter taste. It is soluble in dilute acids, methanol
and chloroform, and practically insoluble in water.
Dipyridamole is BCS class II drug having low solubility and
high permeability. It is soluble at low pH but insoluble in
high pH (i.e., alkaline ph of small intestine ) has a narrow
absorption window and is primarily absorbed in the
stomach, its oral bioavailability is 37 - 66% & biological
half life is also short (40 min). Dipyridamole is highly
bound to plasma proteins. It is metabolized in the liver
where it is conjugated as a glucuronide and excreted with
the bile 1-4.
The low water solubility of the active substance is
responsible for the risks of low oral bioavailability. In
order to enhance the therapeutic efficacy, Dipyridamole
needs an alternative drug delivery system. Cocrystals have
recently drawn significant attention in the delivery of
drugs by enhancing the drug physicochemical properties
such as melting point, solubility, dissolution rate, stability
and bioavailability without changing their chemical
structure 5,6. Cocrystals are compounds with a
stoichiometric ratio of drug substance and cocrystal
coformers (CCFs) (1:1, 1:2, 1:3 or vice versa) 7. These
cocrystals are combined by non-covalent interfaces like
hydrogen bonds, Van Der Waals forces and π-π packaging
which are robust at room temperature 8 , 9, 10, 11. Cocrystal
former is a ballast molecule. Identifying and selecting the
appropriate conformer continues the most important
factor in the effective co-crystal growth 7. This technology
is explored effectively for the delivery of various drugs
such as acyclovir 12, gliclazide 13, piracetam 14, fexofenadine
15, furosemide 16, quercetin 17, baicalein 18, myricetin 19 etc
to improve the therapeutic efficacy.
Figure 1: Structure of Dipyridamole

Gawade et al Journal of Drug Delivery & Therapeutics. 2021; 11(1-s):43-48
ISSN: 2250-1177 [44] CODEN (USA): JDDTAO
The objective of present paper is to enrich the rate of
dissolution, efficacy of Dipyridamole absorption using
solvent assisted griding method. Literature study shows that
there have been few Dipyridamole formulations reported to
date. Dipyridamole was therefore chosen as the poorly
soluble model drug in this work; the solvent assisted
grinding method developed Dipyridamole tartaric acid pH-
independent cocrystals. Fourier transform-infrared
spectroscopy, Differential scanning calorimetry, scanning
electron microscopy and powder X-ray diffraction defined
the cocrystals produced and solubility and dissolution
studies defined the enhancement of solubility and % drug
release.
MATERIALS AND METHODS
Materials:
Dipyridamole was obtained from Micro Advanced Research
Center (Bangalore, India) as a gift sample. Tartaric acid was
collected from Poona Chemical Laboratory. Other reagents
have been bought from S. D. Fine Limited Chemicals
(Mumbai, India).
Methods:
Molecular docking and Selection of coformers
Molecular docking is effective approach for computer aided
structure-based drug discovery. This strategy predicts the
probability of binding and orienting one molecule (API) is
connected to a second molecule (coformer) to form a new
complex 18. The strength of the binding affinity between two
molecules by means of scoring features can be determined 19,
20. Based on the literature, seven coformers were selected for
the preparation of the Dipyridamole cocrystals. The research
of molecular docking was carried out on the seven coformers
chosen. Furthermore, the radar chart was used to visually
compare the quality docking score of coformer information
with an advantage of showing multidimensional information
without the use of statistical methods. Tartaric acid was
verified among the seven coformers based on the potential
for interaction type, compatibility, and docking score for
cocrystals confirmation with Dipyridamole.
Solvent assisted griding method of cocrystallization for
Dipyridamole
Liquid assisted grinding involves the addition of a solvent,
typically in a very small amount, to the dry solids prior to the
initiation of milling. The solvent has a catalytic role in
assisting cocrystal formation and should persist for the
duration of the grinding process. More efficient cocrystal
formation is suggested for liquid assisted methods than with
neat methods.
Dipyridamole cocrystals synthesis was performed using
Liquid assisted grinding technique. Screening of formation of
DYP cocrystals was performed by various coformers in an
optimal molar ratio (1:1, 1:2 and 1:3). A mixture of 1:1
Dipyridamole and tartaric acid (TA) griding was carried out
in mortar and pestle for 30 minutes with the addition of 10
mL ethanol drop wise. And wet crystal was dried in oven and
store in desiccator. Crystals were triturated in mortal and
pestle and stored at room temperature 21, 22.
Figure 2: Preparation of DYP –TA Cocrystals by Solvent assisted griding method
Characterization of DEM cocrystals
Differential scanning calorimetry (DSC)
A differential calorimeter scanning (DSC7020 thermal
analysis system HITACHI) was used for thermal analysis of
DYP, DYP cocrystals samples. Powder samples of
approximately 2.0 mg were placed in aluminum open
crucibles and heated at a rate of 10°C/ min up to 400°C.
Fourier transform-infrared spectroscopy (FT -IR)
FT-IR spectra were registered on a Nicolet iS10
spectrophotometer from 4,000 cm-1 to 500 cm-1 (Thermo
Fisher Scientific, Madison, USA). With 40 scans per spectrum
at a resolution of 0.4 cm-1, DYP cocrystals were obtained and
analyzed using the DTGS KBr detector.
Powder X-ray diffraction (PXRD)
DYP, DYP cocrystals XRD patterns were achieved using
Shimadzu XRD-6000X system at ambient temperature
(Shimadzu, Japan). Samples with Ni-filtered Cu-K (α)
radiations were irradiated at a voltage of 40.0 kV and a
current of 40.0 mA. The scanning rate ranged from 3º to 50º
over a diffraction angle of 2º/min.
Invitro dissolution study
The dissolution studies were performed in a dissolution
apparatus Electrolab, Navi Mumbai using the paddle method
in 900 mL of pH 1.2 and 6.8 phosphate buffer at 75 rpm
maintained at 37±0.5°C. The dissolution medium was added
an amount equal to 75 mg of cocrystals and the samples
were withdrawn at appropriate intervals. The samples were
filtered through Whitman filter paper No. 41, diluted, and
spectrophotometrically analyzed at 282 nm.
RESULTS AND DISCUSSION
Dipyridamole structure consists of two aromatic rings
(pyrimido and pyridine), four hydroxyl groups, eight
aromatic nitrogen atoms . Dipyridamole molecule has four
hydrogen bond donors as well as twelve hydrogen bond
acceptors due to aromatic nitrogen (N) in pyrimidine ring,
pyrimidine ring and hydroxy groups and significant
conformational flexibility; hence it is possible to form co-

Gawade et al Journal of Drug Delivery & Therapeutics. 2021; 11(1-s):43-48
ISSN: 2250-1177 [45] CODEN (USA): JDDTAO
crystals with certain co-formers 23. Depending on the ability
of interaction, hydrogen bond, docking score and
compatibility, tartaric acid was selected as coformer for
preparation of Dipyridamole cocrystals (Figure 2). The
details are summarized in the below Table 1. Figure 3
represents visual comparison of docking score in form of
Radar chart. There are several axes in a radar chart where
the information can be plotted. Every axis is one category.
The information is displayed on the axis as points. It is
possible to join the points belonging to a one data series. A
point near the center of an axis shows a reduced value and
vice versa. Through the visual comparison from Radar charts
and docking score from molecular modeling, tartaric acid
showed the lowest score. Van Der Waals and the
electrostatic energy define the interaction between the API
and coformer. Higher docking results in the potential for
repulsion. In contrast, reduced docking score relates to
reduced potential.
Figure 2: Hydrogen bonding of Dipyridamole- tartaric
acid cocrystals
Figure 3: Application of radar chart to evaluate the coformers
Table 1: Molecular modeling of Coformers
Sr No.
Name
Structure
Docking score
Hydrogen bonding
01
Adipic acid
HO
OOH
O
-1.04
Hydrogen bonding
possible
02
Malic acid
OOHHO O
-1.80
Hydrogen bonding
possible
03
Succinic acid
HO
O
O
OH
0.00
No bonding
04
Nicotinamide
N
NH2
O
0.00
No bonding
05
Sodium acetate
-1.46
No hydrogen bond.
06
Benzoic acid
-1.48
No hydrogen bond.
07
Tartaric acid
-4.135
Hydrogen bonding
possible
Solvent assisted gridding using ethanol as a solvent and
tartaric acid as a coformer resulted in adequate
Dipyridamole cocrystal formation. Preliminary cocrystal
formation evaluation was performed by comparing pure
drug and cocrystals.

Gawade et al Journal of Drug Delivery & Therapeutics. 2021; 11(1-s):43-48
ISSN: 2250-1177 [46] CODEN (USA): JDDTAO
Differential scanning calorimetry (DSC)
An endothermic peak at 156°C represented the melting point
of pure drug. Significant difference in the melting point (156
°C) of cocrystals was observed compared to pure drug
(163°C), sharp endothermic peaks appear at lower
temperatures in comparison to the sharp endothermic peaks
at higher temperatures of the individual components in
Figure 4. This could suggest interaction between the
components, and formation of co-crystallization.
Temp Cel 350.0300.0250.0200.0150.0100.0
DSC mW
0.200
0.000
-0.200
-0.400
-0.600
-0.800
-1.000
DDSC mW/min
Temp Cel 300.0250.0200.0150.0100.0
DSC uW
-50.0
-100.0
-150.0
-200.0
-250.0
-300.0
-350.0
-400.0
-450.0
-500.0
-550.0
DDSC uW/min
57.4Cel
124.3Cel
Figure 4: Differential scanning Calorimetry of a) Dipyridamole and b) Dipyridamole cocrystals
Fourier transform-infrared spectroscopy (FT -IR)
The FTIR showed shifts and changes in the intensity of the
peaks in the DYP and DYP co-crystals, as shown in Figure 9.4.
Hydrogen bonding in the co-crystals was identified by
decreasing the intensity of the O-H peak. A decrease in the N-
H stretching and bending frequency indicates that hydrogen
is involved in hydrogen bonding. The degree of decrease in
frequency and the relative broadening of the band can
determine the magnitude of hydrogen bonding. The role of
the degree and strength of the hydrogen bond is to reduce
the frequency. Significant modifications in the area of
covalent bond between C-C and amine (N-H) stretch have
shown the formation of new hydrogen 24, 25.
Figure 5: FTIR graph of a) Dipyridamole and b) Dipyridamole cocrystals
Powder X-ray diffraction (PXRD)
X-ray diffractograms of DYP showed an intense peak at 2 to
20º signifying the crystalline nature of the drug. DYP
cocrystals showed no intense drug peaks were observed at
2θ of 20º indicating existence of the amorphous phase
(Figure 6). In the case of Dipyridamole cocrystals, however,
there were no intensive drug peaks at 2θ of 20º showing the
presence of the amorphous stage. Decreased intensities and
fewer peaks may be due to changes in crystal habit or
amorphous form. Reduced crystalline characteristics may
result in enhanced dissolution of Dipyridamole compared to
pure drug 26.
Figure 6: XRD spectra of a) Dipyridamole and b) Dipyridamole cocrystals

Gawade et al Journal of Drug Delivery & Therapeutics. 2021; 11(1-s):43-48
ISSN: 2250-1177 [47] CODEN (USA): JDDTAO
Invitro drug release
As reported in literature, Dipyridamole solubility depends
on pH. It is highly soluble in acidic media and poorly soluble
in alkaline media. Dipyridamole is also susceptible to acid
and undergoes degradation. Hence, Dipyridamole cocrystals
were developed by improving the physicochemical
properties. The dissolution experiment was performed on
Dipyridamole and Dipyridamole cocrystals at pH 1.2 and pH
6.8 to verify the pH independent solubility and release of
drugs. The Dipyridamole and Dipyridamole cocrystals
dissolution profile is depicted in Figure 8 and 9. The
Dipyridamole dissolution profile shows that API has a good
rate of dissolution in acidic pH (29.03%) as compared to
alkaline pH 48.1%) % at 30 minutes respectively. The
complete quantity of Dipyridamole dissolved in 45 min was
62% in acid pH and 32 % in alkaline pH. However,
Dipyridamole cocrystals dissolution rate led in a substantial
rise as function of pH independent drug release. The
quantity of Dipyridamole released from cocrystals in the
first 30 minutes was 58.58% and the dissolved quantity was
67.5% at pH 1.2. In the first 30 minutes, the amount of
substance dissolved 82.8% drug release in 30 minutes and
96.48 percent drug release at 45 minutes in pH 6.8 (Figure 8
& Figure 9). In addition, higher dissolution of Dipyridamole
cocrystals can be ascribed to changes in the crystalline
pattern, size and shape of cocrystals that escort to increased
cocrystal solubility in dissolution media 16,24, 27, 32- 37.
Figure 8: Invitro dissolution profile for Dipyridamole and DP-TA cocrystals at pH 1.2
Figure 9: Invitro dissolution profile for Dipyridamole and DP-TA cocrystals at pH 6.8
CONCLUSION:
In the present work prepared Dipyridamole cocrystals
exhibited excellent physicochemical properties (solubility
and dissolution) properties when compared to pure drugs.
From the conducted study, we can conclude that cocrystals
with tartaric acid prepared by technique of solvent assisted
gridding techniques showed an improvement in the
solubility and pH independent drug release, rate of
dissolution and stability compared to pure drug.
ACKNOWLEDGEMENT:
The authors are grateful to Dr. B. S. Kuchekar Dean,
Pharmacy School, Dr. Vishwanath Karad MIT World Peace
University, Pune for offering the required equipment for
conducting the experiment.
Conflict of interest: The authors declare no conflict of
interest.

Gawade et al Journal of Drug Delivery & Therapeutics. 2021; 11(1-s):43-48
ISSN: 2250-1177 [48] CODEN (USA): JDDTAO
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