Improved Dissolution Characteristics of Lovastatin by Inclusion in b-CD and Hp b-CD

 

Ashok Malpani1*, S Appala Raju2 and SN Hiremath3

1K.C.T. College of Pharmacy, Gulbarga-585105,

2H.K.E.S. College of Pharmacy, Gulbarga- 585105

3P.R.E.Society’s, College of Pharmacy, Chincholi, Nashik-422101

*Corresponding Author E-mail:  malpani_ashok@rediffmail.com

 

ABSTRACT

Lovastatin is a hydrophobic molecule practically insoluble in aqueous media and exhibits an exceedingly slow intrinsic dissolution rate. In the present work inclusion complexes of lovastatin were prepared with the soluble complexing agents b-CD and HP b-CD. Phase solubility studies revealed the formation of 1:1 complex of AL type with a stability constant Kc Of 85.91 m-1 and 113.49 m-1  for b-CD and HP b-CD respectively in water. Interactions of the drug b-CD and HP b-CD in the solid state were studied using FTIR, DSC and X-ray powder diffraction studies. Preparation of kneading mixture of drug and HPb-CD increased both the aqueous solubility and the dissolution rate.

 

KEY WORDS:     Lovastatin, b-CD and HP b-CD, Inclusion, dissolution rate

 


INTRODUCTION:

Cyclodextrin’s (CD’s) are hydrophilic, cyclic, non reducing oligosacchrides, compound of 6-8 glucopyranose units and have been extensively used to enhance the solubility of many water insoluble drugs. CD’s have the ability to form inclusion complexes with many drug molecules, in which the guest molecule is entrapped partially or completely within the cyclodextrin cavity thus resulting in an increase in the solubility of drug. The inclusion complexes have been shown to improve solubility, dissolution rate 1, 2, Chemical stability 3,4 and bioavalability,5,6  Complexation may also reduce local irritation and side effects associated with some drugs 7.

 

Lovastatin (LST) is a cholesterol lowering agent is chemically 1,2,3,7,8a- hexahydro –3,7,dimethyl –8-[2- (tetrahydro- 4 - hydroxy -6 – Ox 6-oro-24, pyran – 2- ethyl] – 1 – naphthalenyl-2 methyl butanoale. LST is practically insoluble in water. This limits several advantages of the drug with respect to its absorption, distribution and therapeutic efficacy. Thus the aim of this study was to improve the solubility and dissolution rate of LST in aqueous solution and thereby improve its oral bioavailability. This was attained through the formation of inclusion complexes with b-CD and HP b-CD.

 

MATERIALS AND METHODS:

LST was a gift sample from Cheminova Ltd. Hyderabad and b-CD and HP b-CD was procured as gift sample from S.A Pharmachem. Pvt. Ltd. Mumbai, all other chemicals were of analytical grade.

 

Phase Solubility Studies:

Phase solubility studies were performed according to the method reported by Higuchi and Connor’s8.  Excess LST (50mg) was added to 25ml portion of distilled water each containing various concentrations of b-CD or HP b-CD (i.e. 3 to 15X 10-3 moles / liter)  taken in a series of 50 ml stopperd conical flasks and the mixtures were shaken for 72 hrs at room temperature (280 C) and a rotary flask shaker.  After 72 hrs of shaking to achieve equilibrium, 5 ml aliquots were withdrawn at 1 hr interval and filtered immediately using 0.45m nylon filter. The filtered samples were diluted suitably and assayed for LST by measuring absorbance at 239 mm against blank prepared in the same concentration of b-CD and HPb-CD in water so as to cancel any absorbance that may be exhibited by the cyclodextrin molecule, shaking was continued until 3 consecutive estimates are the same.

 

Preparation of Complexes:

The solid complexes of LST and b-CD, HP b-CD were prepared in 1:1 M and 1:2 M by 2 methods, Physical mixture and Kneading methods. Physical mixture of LST and cyclodextrins in different molar ratios (1:1 M and 1:2 M) were mixed in mortar for about one hour with constant trituration, passed through sieve no.100 and stored in dessicator over fused calcium chloride. In the kneading method LST and cyclodextrin were taken in two different molar ratios (1:1 and 1:2 M.) b-CD or HPb-CD were added to mortar, small quantity of 50% ethanol was added while triturating to get slurry like consistency. Then slowly drug was incorporated into the slurry and trituration was further continued for 1 hr. Slurry was further air dried at 450 C for 24 hr, pulverized and passed through sieve no.100 and stored in dessicator over fused calcium chloride.

 

Fig: 1 (a) PD, (b) β-CD, (c) β-CD 1, (d) β-CD 2, (e) β-CD K1, (f) β-CD K2, (g) HP-β-CD, (h) HP-β-CD 1, (i) HP-β-CD2, (j) HP-β-CDK1, (k) HP-β-CDK2

FTIR ANALYSIS

Characterization of Inclusion Complexes:

Fourier Transformed Infrared Spectral Studies:

The Fourier transformed infrared (FTIR) spectra of Lovastatin and inclusion complexes prepared by different methods in different molar ratios were recorded in a KBr pellets using a JASCO FT / IR – 5300 (Tokyo, Japan) and results are given in Fig.1

 

Differential Scanning Calorimetry (DSC):

Seiko, Japan DSC 220 C- Model differential scanning calorimeter was used. The samples were sealed in aluminum pans and the DSC thermogram were recorded at a heating rate of 100 C / min from 500 C- 300 0C. The DSC thermograms are shown in Fig.2

 

X-ray Diffractometry:

The powder X ray diffraction patterns were recorded using  a Philips diffractometer  model PW 3710 based operated at voltage of 40 Kv and current of  30 mA. The samples were analyzed in the 2θ angle range of 0 – 100 0 and the results are shown in Fig.3  

 

 

Dissolution Rate Studies:

In vitro dissolution studies of pure drug, Physical mixtures, inclusion complexes prepared by different methods were carried out in 900 ml of 0.1 N HCL with 0.25% sodium lauryl sulfate (SLS) using USPXXIII six station dissolution rate test apparatus (Electrolab) with a paddle stirrer, at a speed of 50 rpm and a temperature of 37± 0.50 C were used in each tests. Samples were withdrawn at different time intervals, filtered using a 0.45m nylon disc filter and assayed for LST by measuring absorbance at 239.5nm.The dissolution experiments were conducted in triplicate. The dissolution profiles were evaluated by the dissolution efficiency parameter at 5 min (DE5), according to the method of Khan9.  

 

Fig: 2 (a) PD, (b) β-CD, (c) β-CD 1, (d) β-CD 2, (e) β-CD K1, (f) β-CD K2, (g) HP-β-CD, (h) HP-β-CD 1, (i) HP-β-CD2, (j) HP-β-CDK1, (k) HP-β-CDK2

DSC

RESULTS AND DISCUSSION:

The phase solubility diagram for the complex formation between LST and β-CD, LST and HP β-CD is shown in figure 4. The aqueous solubility of LST increased linearly (r =0.995) as a function of β-CD concentration .The phase solubility diagram can be classified as type AL according to Higuchi and Connors classification, because the straight line had a slope less than unity, it was due to the formation of a 1:1 M complex. The apparent stability constant, Kc was calculated from the linear plot of the phase solubility diagram according to the equation, Kc = Slope/So (1-slope)

 

Where So is the solubility of LST in the absence of β- CD or HP β-CD. The stability constant of LST- β-CD was found to be 85.91 M-1. The phase solubility diagram for LST was linear (Higuchi,s AL-type) at HP β-CD concentration  from O-15 mM/litre and stability constant for LST-HP β- CD was found to be 113.49 M-1. By comparing the slopes of phase solubility diagram, the solubilising effect of   HP β-CD on LST appears to be more in water when compared to β-CD. 

FTIR spectrum of pure drug and various complexes are shown in fig 1. FTIR Spectrum of LST exhibited peak at 1698.64 cm -1 due to C=O of ester and peak at 121and.and8 cm -1 due to C–O stretching of ester. Peaks at 3542.79 cm -1 and 1382.16 cm -1 are due to O–H Stretching and O–H deformation. The IR Spectrum of Lova – β-CD 1:1 and 1:2 Complexes exhibited peak at 1698.78 cm -1 due to C=O stretch and peak at 1218.00 cm -1 is due to C–O Stretch of ester and peak at 1368.78 cm -1 is due to O–H deformation instead of 1382.16 cm -1 and peak at 3390.06 cm -1 due to O–H stretch instead of 3542.79 cm -1  indicate undisturbed drug in formulations both in complexes prepared by physical mixing and kneading methods. However, shift in peaks in IR spectrum of formulation indicates the interaction between the drug and base. In case of LST – HP β-CD complexes prepared by kneading method exhibited peak at 1699.05 cm -1 is due to C=O stretch and peak at 121and.33 cm -1 due to O–H deformation and peak at 3389.93 cm -1 and 3378.21 cm -1 due to O–H stretching confirms the drug structure. The reduction in the intensity of bands due to restriction to vibration imposed by the host molecule when it was enclosed in the CD cavity. The slight shift in peaks and reduction in the intensity of bands showed the interaction between LST and HP β-CD in kneaded complexes.

 

 

Fig: 3 (a) PD, (b) β-CD, (c) β-CD 1, (d) β-CD 2, (e) β-CD K1, (f) β-CD K2, (g) HP-β-CD, (h) HP-β-CD 1, (i) HP-β-CD2, (j) HP-β-CDK1, (k) HP-β-CDK2

RD

Table: 1 Percent Dissolution Efficiency (DE5) of pure LST and various inclusion complexes

S. No

Formulations

Code

DE5 (%)

1

LST

PD

09.40

2

LST-β-CD PM (1:1)

β-CD1

41.20

3

LST-β-CD PM (1:2)

β-CD2

63.20

4

LST-β-CD KC (1:1)

β-CDK1

70.70

5

LST-β-CD KC (1:2)

β-CDK2

38.00

6

LST-HP-β-CD PM (1:1)

HP-β-CD1

77.20

7

LST-HP-β-CD PM (1:2)

HP-β-CD2

63.50

8

LST-HP-β-CD KC (1:1)

HP-β-CDK1

69.70

9

LST-HP-β-CD KC (1:2)

HP-β-CD K2

80.90

 

The thermal behavior of LST – cyclodextrin complexes were studied using DSC in order to confirm the formation of the solid complexes. DSC thermograms of LST, LST – β-CD and LST – HP β-CD complexes are shown in figure 2. The DSC thermograms of LST exhibited an endothermic peak at 165.06 0C corresponding to its melting point. β-CD showed a broad endothermic peak at 89.510C which may be attributed to a dehydration process. The DSC thermogram of LST – β-CD (1:1M and 1:2 M ) prepared by physical mixture exhibited endothermic peak at 153.70 0C , 161.65 0C, 162.22 0 C and 157.110C instead of 165.060 C which was observed in the thermogram of pure LST. This slight shift in endothermic peak indicates the interaction between LST and β-CD.

 

Fig: 4 Phase solubility studies of LST with b-CD (a) and HP-bCD (b) in water

 

The DSC thermogram of HP β-CD exhibited an broad endothermic peak at 94.050C may be due to dehydration process. The thermogram of LST – HP β-CD prepared by physical mixture shows slight shift in peaks indicating weak interaction (Peak at 161.080C and 162.790C). where as complexes prepared by Kneading method showed greater shift in peaks indicating strong interaction between drug and HP β-CD ( 153.130C and 170.740C).

 

The X-ray powder diffractogram of the pure components, the physical mixture and kneaded inclusion complexes are shown in figure 3. The diffraction pattern of the physical mixture is simply the superimposition of each component with the peak observed with pure drug. On the other hand, the diffraction pattern of kneaded complexes exhibited less peaks with lower intensity. This indicates that the inclusion complexes prepared by kneading method are markedly less crystalline then the physical mixture of pure drug.

 

The dissolution profiles of LST and LST- cyclodextrin complexes prepared by different methods are shown in figure 5 and 6. The dissolution of pure drug was incomplete even after 120min, releasing only 35.5% of LST in 120min. All cyclodextrin complexes showed faster release with respect to LST alone. The dissolution of LST from the HP β-CD systems was higher than from the corresponding β-CD systems. The best effectiveness of HP β-CD may be due to its greater water solubility effect, higher wetting and solubility effect. The dissolution of LST from kneaded products were found to be faster than the physical mixtures. The percentage of dissolved drug is nearly 1.5% for the pure drug and above 85% when complexed with β-CD and more than 90% when complexed with HP β-CD after 10min. When dissolution efficiency DE5 values were compared, the values were higher for kneaded products than the physical mixtures and pure drug (Table 1). The significant enhancement of dissolution efficiency values with kneaded products may be due to increased solubility of lovastatin upon complexation and also because of amorphous state due to the reduction of crystallinity following complexation.

 

Fig: 5 Dissolution profile of LST and its HP-bCD complexes

 

Fig: 6 Dissolution profile of LST and its bCD complexes

 

CONCLUSION:

LST was found to form inclusion complexes with β-CD and HP β-CD. Kneading methods were found to be appropriate techniques to achieve complexation when compared to the corresponding physical mixtures.

 

ACKNOWLEDGEMENT:

We are grateful to Artemis Biotech Hyderabad for providing the gift sample of LST and SA Pharmachem Pvt.Ltd for providing the gift samples of βCD and HP- βCD. We are also thankful to Director K.C.T college of pharmacy for providing facilities to carry out the work.

 

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Received on 27.09.2008           Modified on 14.10.2008

Accepted on 23.10.2008          © RJPT All right reserved

Research J. Pharm. and Tech. 2(1): Jan.-Mar. 2009; Page 110-113