Paracetamol is a sparingly soluble bitter tasting drug. It is widely used as an analgesic and antipyretic. Complexation of drug with different cyclodextrins (?, ? and HP-?-CD) was attempted to improve solubility of Paracetamol. During the drug excipient interaction studies, ?, ? cyclodextrins elicited analytical interference and showed considerable absorbance at ?max (243.5 nm) of Paracetamol while the ones constituting of hydroxypropyl-beta-cyclodextrin (HP-?-CD) did not show any such interference. Therefore, the present study is concentrated on exploring HP-?-CD as complexing agent. Phase solubility studies showed that complexation of Paracetamol/HP-?-CD at molar ratio 1:1 and showed AL type solubility curve. Complexation was done by various methods like physical mixing, kneading and freeze drying and resulting drug complexes were characterized by Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared Spectroscopy (FTIR). The thermograms obtained showed an endothermic peak for Paracetamol, for physical mixture to some extent for kneaded mixture, but was completely eliminated for freeze dried product (Inclusion complex). Similar results were obtained during IR studies. Therefore, solid inclusion complex of paracetamol prepared by freeze drying method was found to be an ideal complex. The solubility of paracetamol, was significantly increased (six folds of normal solubility) by complexation with HP-?-CD.
Acute and Subchronic Toxicity?of Teucrium polium Total Extract in Rats
Iranian Journal of Pharmaceutical Research (2007)
6 (2): 95-99
Received: October 2005
Accepted: May 2006
Copyright ? 2005 by School of Pharmacy Shaheed Beheshti University of Medical Sciences and Health Services
Development and Characterization of Paracetamol Complexes
Sushma Talegaonkar*, Azhar Yakoob
Khan, Roop Kishan Khar, Farhan Jalees Ahmad
and Zeenat I. Khan
Department of Pharmaceutics, Faculty of Pharmacy, Jamia Hamdard,
New Delhi, 110062, India.
Paracetamol is a sparingly soluble bitter tasting drug. It is widely used as an
analgesic and antipyretic. Complexation of drug with different cyclodextrins (α,
β and HP-β-CD) was attempted to improve solubility of Paracetamol. During the
drug excipient interaction studies, α, β cyclodextrins elicited analytical
interference and showed considerable absorbance at λmax (243.5 nm) of
Paracetamol while the ones constituting of hydroxypropyl-beta-cyclodextrin
(HP-β-CD) did not show any such interference. Therefore, the present study is
concentrated on exploring HP-β-CD as complexing agent. Phase solubility studies
showed that complexation of Paracetamol/HP-β-CD at molar ratio 1:1 and showed AL
type solubility curve. Complexation was done by various methods like physical
mixing, kneading and freeze drying and resulting drug complexes were
characterized by Differential Scanning Calorimetry (DSC) and Fourier Transform
Infrared Spectroscopy (FTIR). The thermograms obtained showed an endothermic
peak for Paracetamol, for physical mixture to some extent for kneaded mixture,
but was completely eliminated for freeze dried product (Inclusion complex).
Similar results were obtained during IR studies. Therefore, solid inclusion
complex of paracetamol prepared by freeze drying method was found to be an ideal
complex. The solubility of paracetamol, was significantly increased (six folds
of normal solubility) by complexation with HP-β-CD.
Cyclodextrins have been reported in a number of studies in the pharmaceutical
field to form inclusion complexes with several pharmaceutical drugs.
Cyclodextrins have been extensively used for improving solubility (1-3)
stability (4, 5) and bioavailability (6, 7) of drugs. In recent years,
hydroxypropyl-β-cyclodextrin has gained appreciable acceptance among the various
types of cyclodextrins. Large number of inclusion complexes of HP-β-CD with a
wide range of drugs have been published and patented all over the world. Various
methods for inclusion complexes like grinding, kneading, freeze drying, spray
drying, slow evaporation etc have been widely reported. Freeze drying and spray
drying techniques are most efficient techniques but of these the freeze drying
method has not been much explored.
In previous studies, inclusion complexes of Paracetamol with β-cyclodextrin have
been prepared and characterized to improve the solubility and dissolution of
paracetamol (8, 9). But the low aqueous solubility of β-CD (About 1.8% w/v at
25?C) limits its use nowadays and other more soluble cyclodextrin derivatives
have been utilized. Hydroxypropyl-β-cyclodextrin (HP-β-CD) owing to its high
solubility, is one of the most frequently used cyclodextrin derivative today
(about 50% w/v at 25?C). Good oral and parenteral tolerability are its further
The present study attempted at increasing the solubility of the paracetamol by
using different cyclodextrins. Amongst these, complexes of HP-β-CD with
Paracetamol was found to be most suitable as it did not exhibit any analytical
interference/ absorbance and hence it was zeroed on for further investigations.
Paracetamol was obtained from Orient Pharma and chemicals, New Delhi and
HydroxyPropyl-Beta-Cyclodextrin was a gift sample from Ranbaxy laboratories. All
other chemicals were of analytical grade.
Phase solubility studies
The stability constant for the inclusion complex formed between paracetamol and
HP-β-CD was determined using the phase solubility method which was carried out
according to Higuchi and Connors (10). Briefly, an excess amount of paracetamol
was added to the aqueous solutions (10 ml) of cyclodextrin of varying
concentration (5-25 mM). Fresh distilled water was used as medium and flasks
were protected from light, sealed and were placed in a waterbath shaker for 72
h. After equilibrium was reached the sample of each flask was filtered through
millipore filter (0.45 μm). The filtered solution was then diluted and
concentration of paracetamol was analysed by U.V spectrophotometer (Shimadzu
Double Beam Spectrophotometer 1601) at 243.5 nm. The work was performed at
35?2?C in triplicate upto a level when the last reading showed the same amount
of absorption, indicating the maximum solubility (Figure 1).
Preparation of the physical mixture/grinding
Paracetamol and HP-β-CD (Molar ratio 1:1) were weighed accurately, pulverized
and then mixed thoroughly (30 min) by light trituration in a glass mortar until
a homogenous mixture was obtained. The resultant mixture was stored in a
Preparation of inclusion complexes
Equimolar quantities of the paracetamol and HP-β-CD were mixed in a mortar and
pestle for 10 min which was then kneaded with a mixture of water and ethanol
(1:1) for 60 min. Kneading was done till the product started drying on the walls
of mortar. The product was further dried in an oven at 40?C for 30 min until a
constant weight was obtained. The resultant product was sieved and stored in a
Equimolar quantities of paracetamol and HP-β-CD were taken separately in 20 ml
of water and mixed thoroughly. The resultant solution was frozen in a deep
freezer (New Brunswick Scientific, Germany) at -70?C for about 6 h. The frozen
mixture was then freeze dried in the freeze dryer (Heto drywinner with rotary
vane pump, Germany) for 8 h at -110?C to -120?C under vacuum. The resultant
product was sieved and stored in a dessicator.
Characterization of solid inclusion complexes
Fourier Transform Infrared Spectroscopy (FTIR)
The FTIR spectra of all samples were recorded on Perkin Elmer instrument using
KBr disc method. 10 mg of dried sample was mixed with 40 mg of KBr by using a
clean glass pestle and mortar. The mixed homogenized powder was compressed in an
IR pellet machine to get the pellets which were used immediately for recording
the spectra from 400 to 4000 cm-1.
Differential Scanning Calorimetry (DSC)
DSC was performed by using Perkin Elmer Pyris-6DSC system using 3 mg sample in
crimped aluminium pans at a heating rate of 10?C/min in the range of 50-250?C.
Partition Coefficient Determination
The partition coefficient of the drug and complexes between octanol/water was
determined at ambient temperature (30?2?C). Ten milliliters each of octanol and
distilled water were taken in a glass stoppered flasks, to which 10 mg of
accurately weighed drug was added and the mixture was then shaken with the help
of mechanical shaker for 24 h at room temperature. The mixture was then
transferred to a separating funnel and allowed to equilibrate for 6 h. The
aqueous and octanol phase were separated and filtered and drug content in
aqueous phase was analyzed by UV spectoophotometer at 243.5 nm. The partition
coefficient was calculated.
The equilibrium solubility of paracetamol and complex was determined in
distilled water (10). An excess amount of the drug was shaken in separate flasks
with distilled water and different pH buffers using a mechanical shaker at room
temperature (25?2?C) for 24 h. The sample was then filtered and analyzed by UV
spectoophotometerat 243.5 nm.
Graph Pad InStat version 3.05 was used for statistical analysis of partition
coefficient results. An unpaired, two tailed, t-test was used for analyzing the
significance at p<0.05.
Results and Discussion
Phase solubility study of Paracetamol with HP-β-CD was carried out in distilled
water at temperature 35?2?C (Figure 1). The solubility of paracetamol increases
linearly with increasing concentrations of HP-β-CD. Thus, showing a typical
AL-type phase solubility curve. According to Higuchi and Connors (10), these AL
type curves indicate the formation of complex between the substrate (paracetamol)
and the ligand (HP-β-CD) and a first order dependency of the interactions on the
cyclodextrin concentration. The regressed curve has a slope value 0.0407,
intercept 10.189?10-2 mM and correlation coefficient of 0.9768.
The apparent stability constant Kc was calculated according to the method of
Higuchi and Connors (10) by using the following formula.
Kc = Slope / Intercept (1-Slope)
where Kc is stability constant of inclusion complex.
The stability constant (Kc) for paracetamol was found to be 416.4 M-1 .
Therefore, it can be concluded that Paracetamol will form a stable complex of
drug with HP-β-CD in 1:1 molar ratio.
There are several methods for the preparation of the cyclodextrin-guest
complexes depending on the physical properties of the guest molecules, including
physical mixing, kneading and freeze drying. Lyophilization was used in this
study because it is suitable for substances like paracetamol which are sparingly
water soluble or for drugs which decompose on drying (11). For each method,
complexes were prepared in a molar ratio of 1:1.
Complexation was done by physical mixing, kneading and freeze drying methods
(1:1 molar ratio) and the resulting drug complexes were characterized.
FTIR spectrum of paracetamol (Figure 2) showed absorption bands for hydroxyl
groups at 3324 and 3162 cm-1 , unsaturation (1653, 1610 cm-1 ) and aromatic ring
(1562, 1505, 836 cm-1 ). HP-β-CD spectrum exhibited absorption bands of hydroxyl
group at 3405 cm-1 and vibration bands of C-O and O-H groups at 1083 cm-1 and
1032 cm-1 respectively. The FTIR spectrum of the complexes showed only one broad
absorption band for hydroxyl group at 3384 cm-1 which is due to complexation of
the drug with HP-β-CD (Intermolecular hydrogen bonding of paracetamol with
Although the results obtained by the solubility studies indicate the formation
of a true complex of paracetamol-HP-β-CD, they do not perclude the possibility
that the product is simply a physical mixture. Thus, the thermal behaviour of
cyclodextrin inclusion complex was studied by DSC in order to confirm the
formation of the above mentioned complex. When the guest molecules are
incorporated in the cyclodextrin cavity or in the crystal lattice their melting
point and boiling point usually shift to different temperatures or disappears
within the temperature range when cyclodextrin lattice is decomposed. This is
one of the best method for detecting drug-cyclodextrin complexation.
The DSC thermogram of paracetamol, HP-β-CD and complexes prepared by different
methods are shown in Figure 3. The DSC thermograms of paracetamol show one sharp
characteristic endothermic peak at 171.46?0.82?C and ∆H=274.86?3.8 J/g which is
indicative of its melting temperature. In case of HP-β-CD owing to its amorphous
nature, a broad endothermic peak was observed at about 60?C. The physical
mixture of paracetamol with HP-β-CD shows an endothermic peak at 171.41?0.67?C
while the solid inclusion complex formed by kneading method showed a new
endotherm with decrease in enthalpy (∆H=21.62?6.3 J/g) which is indicative of
fusion of paracetamol with HP-β-CD. In contrast to this, a complete
disappearance of the endothermic peak of paracetamol in the freeze dried complex
is attributed to formation of a true inclusion complex. This is in agreement
with the previous findings suggesting the incorporation of the drug molecule
into the crystal lattice of HP-β-CD. Therefore, complex prepared from this
method was adopted for further study.
Solubility of paracetamol in distilled water was found to be 13.69?1.2 mg/ml at
room temperature. The complexation of paracetamol with HP-β-CD resulted in more
than six fold (79.30?4.2 mg/ml) increase in solubility. This high increase in
the solubility can be attributed to amorphous nature of the complex being formed
The partition coefficient of paracetamol was found to be 2.70 ?0.14 while for
the freeze-dried complex it was estimated as 2.23?0.08. The statistical analysis
of the data revealed a p value of 0.0072, showing a significant difference in
partition coefficient. This difference can be attributed to the enhanced
hydrophilicity, which was primarily due to amorphous nature of the
Amongst the various cyclodextrins explored for the study,
hydroxypropyl-β-cyclodextrin yielded most favorable results in terms of the
drug-cyclodextrin compatibility. While eliciting an augmentation in the
solubility, it also showed an appreciable hydrophilicity. Moreover, the freeze
drying technique offers itself as a potential tool for the complexation of
sparingly soluble drugs.
The authors are thankful to All India Council of Technical education (AICTE) for
its financial support. The Authors are also thankful to Dr. Amir Azam for
carrying out the IR studies and also to Prof. M. Ali for interpreting the IR
Veiga H, Teixeira-Dias JJC, Kedzierewicz F, Sousa A and Mamcent P. Inclusion
complexation of tolbutamide with β-cyclodextrin and
hydroxypropyl-β-cyclodextrin. Int. J. Pharm. (1996) 129: 63-71
Becket G, Schep LJ and Tan MY. Improvement of the in vitro dissolution of
praziquantal by complextion with α-, β- and γ-cyclodextrins. Int. J. Pharm.
(1999) 179: 65-71
Cappello B, Carmingnani C, Iervolino M, Immacolata M, Rotonda L and Saettone MF.
Solubilization of tropicamide by hydroxypropyl-β-cyclodextrin and water soluble
polymers: in vitro/in vivo studies. Int. J. Pharm. (2001) 213: 75-81
Lin HS, Chean CS, Ng YY, Chan SY and Ho PC. 2-hydroxypropyl-beta-cyclodextrin
increases aqueous solubility and photostability of all-trans-retinoic acid. J.
Clin. Pharm. Ther. (2000) 25: 265-269
Liu X, Lin HS, Thenmozhiyal JC, Chan SY and Ho PC. Inclusion of Acitretin into
cyclodextrins: Phase solubility, photostability study and physicochemical
characterization. J. Pharm. Sci. (2003) 92: 2449-2457
Wong JW and Yuen KH. Improved bioavilability of artemisnin through inclusion
complexation with β- and γ- cyclodextrins. Int. J. Pharm. (2001) 227: 177-185
Liu X, Lin HS, Chan SY and Ho PC. Biopharmaceutics of β-cyclodextrin
derivative-based formulations of Acitretin in sprague-dawley rats. J. Pharm.
Sci. (2004) 93: 805-815
Lin SY and Kao YH. Solid particulate of drug-β-cyclodextrin inclusion complexes
directly prepared by a spray drying technique. Int. J. Pharm. (1989) 56: 249-259
Tasic LM, Jovanovic D and Djuric ZR. The influence of β-cyclodextrin on the
solubility and dissolution rate of paracetamol solid dispersions. J. Pharm.
Pharmacol. (1992) 44: 52-55
Higuchi T and Connors KA. Phase solubility techniques. In: Reilley CN. (ed.)
Advances in Analytical Chemistry and Instrumentation. Vol 4, Interscience, New
York (1965) 117-212
Saenger W. Cyclodextrin inclusion compounds in research and industry. Angew.
Chem. Int. Ed. Eng. (1980) 19: 344-362