ENHANCEMENT OF SOLUBILITY OF RITONAVIR BY USING...

RESEARCH ARTICLE K. Sai Saran et.al / IJIPSR / 1 (2), 2013, 266- 280

Department of Pharmaceutics ISSN (online): 2347-2154

Available online: www.ijipsr.com October Issue 266

ENHANCEMENT OF SOLUBILITY OF RITONAVIR BY USING SOLID

DISPERSION TECHNIQUE

1K.Sai Saran*,

2M.Srujan Kumar,

3Dr.K.V.Subrahmanyam

1M.Pharmacy Scholar, Samskruti College of Pharmacy, Hyderabad, INDIA.

2Faculty, Samskruti College of Pharmacy, Hyderabad, INDIA.

3Principal, Samskruti College of Pharmacy, Hyderabad, INDIA.

Corresponding Author:

K. Sai Saran

13-6-460/10/1/A,B1,first floor

Mahesh nagar colony, gudimalkapur

Mehdipatnam-500028

Email: [email protected]

International Journal of Innovative

Pharmaceutical Sciences and Research www.ijipsr.com

Abstract

Ritonavir is an antiretroviral drug characterized by low solubility and high permeability which corresponds to

BCS class II drug. The purpose of the study was to develop solid dispersion by different methods and investigate

them for in vitro and in vivo performance for enhancing dissolution and solubility. The solid dispersion was

prepared using PEG 6000, Crosspovidone, sorbitol, mannitol as carriers in different ratios by different methods

and was characterized for FT-IR. In vitro dissolution studies were performed in 0.1 N HCl and biorelevant media

showed enhanced dissolution rate as compared to marketed formulation. The dissolution of prepared formulation

(F10) was relatively higher (96%) than marketed formulation. On the basis of the result obtained, it was

concluded that solid dispersion is a good approach to enhance solubility of poorly water-soluble ritonavir.

Key words: Ritonavir, solid dispersion, PEG 6000, crospovidone, sorbitol.




INTRODUCTION

The solubility of drug remains one of the most challenging aspects in formulation and

development. From literature survey it can be revealed that almost 40 % of all new chemical

entities suffer from poor aqueous solubility and hence suffer from poor absorption and

bioavailability problems. It is generally recognized that low solubility or poor dissolution often

become a rate limiting step in absorption of poorly water soluble drug from gastro intestinal tract

and compromise oral bioavailability. Of the several approaches to improve solubility of poorly

water soluble drug, solid dispersion technique is widely used to improve the water solubility and

in turn dissolution of poorly water soluble drug.

Aqueous solubility of any therapeutically active substance is a key property; it governs

dissolution, absorption and thus the even in vivo efficacy. To improve the dissolution and

bioavailability of poorly water-soluble drugs, researchers have employed various techniques

Chio and Serajuadin used the solid-dispersion technique for dissolution enhancement of poorly

water-soluble drugs.

Being a BCS Class II drug, it often shows dissolution rate-limited oral absorption and high

variability in pharmacological effects. The half life of ritonavir is 3-5 hrs. Therefore

improvement in its solubility and dissolution rate may lead to enhancement in bioavailability.

The aim of the present study was to improve the solubility and dissolution rate of a poorly water

soluble drug, ritonavir by solid dispersion technique.

The term solid dispersion refers to a group of solid products consisting of at least two different

components generally a hydrophilic matrix and a hydrophobic drug. The matrix can be either

crystalline or amorphous. The drug can be dispersed molecularly, in amorphous particles

(clusters) or in crystalline particles. Chiou and Riegelman defined solid dispersions as “the

dispersion of one or more active ingredients in an inert excipient or matrix, where the active

ingredients could exist in finely crystalline, solubilized, or amorphous states” [1].

Sekiguchi and

Obi in 1961 first developed the concept of solid dispersion to enhance absorption of poorly

water-soluble drugs. It involved the formation of eutectic mixtures of drugs with water-soluble

carriers by melting of their physical mixtures, and once the carriers dissolved, the drug

precipitated in a finely divided state in water. Later, Goldberg et al. demonstrated that a certain




fraction of the drug might also be molecularly dispersed in the matrix, forming solid solutions,

while other investigators reported that the drug might be embedded in the matrix as amorphous

materials [2].

Classification of Solid dispersions [2]

Solid dispersions have been classified as follows depending on the type of carrier used for

their preparation (Figure.1)

Fig 1: The Classification of Solid Dispersions

Solubility Enhancement Strategies in Solid Dispersions

Melting and solvent evaporation methods have been the two major processes of preparing

solid dispersions melting on lab scale [3]. Industrially relevant and applicable methods for solid

dispersion manufacturing are explained in Figure (2)

Fig 2: Manufacturing processes used to produce solid dispersions

The objective of the study is to prepare Ritonavir solid dispersion by direct compression

technology using different polymers to achieve the enhanced solubility and to determine the

Kinetic Modeling of Drug Release.




MATERIALS AND METHOD

Ritonavir Supplied by Pharma Train., Hyderabad. Polymers like PEG6000, Crosspovidone,

Sorbitol, Mannitol, Microcrystalline cellulose, Aerosil, Magnesium Stearate supplied by Pharma

Train Research Lab, Hyderabad.

Characterization of the formulation

Pre formulation study

Preformulation stability studies are usually the first quantitative assessment of chemical

stability of a drug as well as stability in presence of other excipients. The primary objectives of

this investigation are identification of stable storage conditions for drug in the solid state and

identification of compatible excipients for a formulation. Preformulation studies were performed

on the drug, which include melting point determination, solubility and compatibility studies.

Melting point: Melting point of Ritonavir was determined by capillary method.

Solubility: Solubility of Ritonavir was determined in water, methanol, methylene chloride, ethyl

ether and buffers.

Preparation of standard curve of ritonavir

Reagents: Methanol, 0.1N Hcl

Standard solution of ritonavir

100mg of drug is dissolved in 100ml of methanol. This is first stock solution.10ml of 1st

stock solution is diluted with 100ml of buffer. This is 2nd

stock solution. Now from 2nd

stock,

various concentrations of 10ug/ml, 15ug/ml, 30ug/ml, and 45ug/ml were prepared by using

buffer. Blank was also prepared with same buffer composition except the drug. UV scanning was

done for pure drug 200-300nm in methanol. The lambda max was found at 239nm.

Compatibility studies

Compatibility with excipients was confirmed by FTIR studies. The pure drug and its

formulation along with excipients were subjected to FTIR studies. In the present study, the

potassium bromide disc (pellet) method was employed.




Fourier Transform Infrared Spectroscopy (FTIR) Interpretation: The infrared spectra of

pure Ritonavir samples were recorded by SHIMADZU 84005 FTIR spectrometer, equipped with

an Inferometer detector. Samples were prepared by KBr disc method (2 mg sample in 100 mg

KBr) and examined in the transmission mode. Each spectrum was measured over a frequency

range of 4000–400 cm−1.The software used for the data analysis was Perkin-Elmer Spectrum

3.02. The peaks obtained in the spectra were then compared with corresponding functional

groups in the structures of Ritonavir.

Formulation Development

Table 1: Composition of solid dispersion tablets

Ingredients F1

(mg)

F2

(mg)

F3

(mg)

F4

(mg)

F5

(mg)

F6

(mg)

F7

(mg)

F8

(mg)

F9

(mg)

F10

(mg)

Ritonavir 100 100 100 100 100 100 100 100 100 100

PEG6000 10 10 50

Copovidone

50

Sorbitol 75 100 150 100 75 100 150 75 75

Mannitol 100

Extragranular exicipents

MCC 110 85 35 75 75 110 85 35 60 60

Cross povidone 13 13 13 13 13 13 13 13 13 13

Aerosil 1 1 1 1 1 1 1 1 1 1

Magnesium stearate 1 1 1 1 1 1 1 1 1 1

Total 300 300 300 300 300 300 300 300 300 300

Preparation of Tablets:

Method 1

Sorbitol was melted in crucible china dish at 100-120º.For batches with PEG add it along

with sorbitol and heat around 50-70º as the Tg of sorbitol is lowered because of PEG. Sift all the




extra granular excipients through mesh no 40 and add these to granules obtained in step 2 and

blend. Compress using suitable punch.

Method 2

Dissolve the drug in ethanol and transfer this solution to carry to make slurry. And with

batches containing copovidone/PEG add these to drug solution. Dry the slurry at 50-60º to

evaporate ethanol completely. Pass the dried granules through mesh no 40. Sift all the extra

granular excipients through mesh no 40 and add these to granules obtained in step 2 and blend.

Compress using suitable punch.

Pre compression studies

Pre compression studies like Bulk density, Tap density, Angle of repose, Compressibility index,

Hausner’s ratio was carried out for the formulation.

Post compression studies

Post compression studies like Hardness, Friability, Content uniformity, Weight variation, In vitro

drug release studies and Release Kinetics was carried out for the prepared formulations.

In-vitro release studies [4-8]

In-Vitro drug release studies were carried out using Tablet dissolution test apparatus

USPXXIII at 50 rpm. The dissolution medium consisted of 900 ml Standard buffer 0.1N HCL.

The temperature was maintained at 370C1

ºC.The sample of 5ml was withdrawn at

predetermined time intervals and an equivalent amount of fresh dissolution fluid equilibrated at

the same temperature was replaced. The samples withdrawn were filtered through Whattman

filter paper (No.1) and drug content in each sample was analyzed by UV-visible

spectrophotometer at 239nm.

Release kinetics [9-11]

The results of in vitro release profile obtained for all the formulations were plotted in

modes of data treatment as follows.

Cumulative percent drug release versus time

(zero order kinetic model)

Log cumulative percent drug remaining versus time

(first order kinetic model)




RESULTS AND DISCUSSION

In the present study 10 formulations were prepared and evaluated for pre formulation

characteristics compatibility studies, pre compression characteristics, post compression

characteristics, invitro release studies and release kinetics.

Pre formulation studies

Melting point

Melting point of Ritonavir was found to be in the range of 120-1230c which complied with the

standard, indicating purity of the drug sample.

Solubility

It is freely soluble in methanol and ethanol, soluble in isopropanol and

practically insoluble in water.

Compatibility Study

Compatibility studies were performed using FT-IR spectrophotometer. The FT-IR spectrum of

pure drug (fig 3) and physical mixture of drug and polymers (fig 8) were studied. The

interpretation results were summarized in table no (2)

Table 2: FTIR Interpretation

S No Wave number(cm-1

) Type of stretch

1 3355 N-H

2 1714 C=O

3 2964 C-H

4 1618 10&2

0 Amines




Fig 3: FTIR spectra of Ritonavir Fig 4: FTIR Spectra of Ritonavir and all excipients

Fig 5: FTIR spectra of Ritonavir and PEG6000 Fig 6: FTIR Spectra of Ritonavir and crospovidone

Fig 7: FTIR spectra of Ritonavir and Sorbitol Fig 8: FTIR Spectra of Ritonavir and Mannitol




Fig 9: FTIR spectra of Ritonavir and MCC Fig10: FTIR of Ritonavir & Croscaramellose sodium

Standard curve of Ritonavir

Standard curve of Ritonavir was determined by plotting absorbance V/s concentration at

239 nm and it follows the Beer’s law. The results were shown in table no (3). The r2 value was

found to be 0.998.

Table 3: Standard curve of Ritonavir

S.No Concentration (µg/ml) Absorbance at 239nm

1 10 0.221

2 20 0.405

3 30 0.581

4 40 0.76

5 50 0.944

Figure 11: Standard curve of Ritonavir




Pre compression studies

Table 4: Pre compression parameters

Formulation

code

Bulk Density

(g/cc)

Tapped density

(g/cc)

Angle of

repose (degree)

Carr’s index

(%)

Hausner ratio

F1 0.49 0.57 27.40 14.04 1.16

F2 0.48 0.55 26.06 12.72 1.14

F3 0.46 0.53 24.38 13.20 1.15

F4 0.43 0.49 23.72 12.24 1.14

F5 0.41 0.47 21.94 12.76 1.14

F6 0.49 0.57 27.40 14.04 1.16

F7 0.46 0.53 24.38 13.20 1.15

F8 0.41 0.47 21.94 12.76 1.14

F9 0.43 0.49 23.72 12.24 1.14

F10 0.48 0.55 26.06 12.72 1.14

Post compression studies:

Table 5: Post compression parameters

S.No. Formulation

Weight variation Hardness (kg/cm2) Diameter (mm)

Thickness

(mm)

Friability (%)

1 F1

complies 3.24 9.0 4.01 0.60




In-Vitro Drug Release Studies

According to USP, dissolution test for ritonavir tablets was done by using 0.1N HCL for 1hr at

50rpm using USP type 2 dissolution apparatus.

Table 6: In-Vitro Drug Release of formulations

Time(hrs) F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 Marketed

formulation

10 30 35 35 34 45 40 45 45 51 55 38

15 42 50 51 55 60 53 55 58 62 66 53

30 50 64 70 74 75 64 70 75 76 88 70

45 70 80 88 92 95 78 87 91 94 96 86

2 F2

complies 3.50 9.2 4.05 0.51

3 F3

complies 3.04 9.5 4.03 0.37

4 F4

complies 3.62 9.4 4.01 0.49

5 F5

complies 3.75 9.1 4.02 0.85

6 F6

complies 3.34 9.4 4.04 0.51

7 F7

complies 3.24 9.5 4.02 0.49

8 F8

complies 3.90 9.2 4.00 0.41

9 F9

complies 3.74 9.0 4.04 0.69

10 F10

complies 3.45 9.1 4.05 0.55




Fig 12: Dissolution profile of F1-F3 Fig 13: Dissolution profile of F4-F6

Fig 14: Dissolution profile of F7-F9 Fig 15: Dissolution profile of F10

Fig 16: Dissolution profile of optimized & marketed formulation

Release kinetics

R2

value s for optimized formulations were summarized in the table no (7).

Table 7: R2 values for optimized formulation

Formulation Zero order First order

Optimized formulation 0.8962 -0.995




Fig 17: Zero order plot Fig 18: First order plot

All the prepared formulations were tested for physical parameters like weight variation,

thickness, hardness and friability found to be within the pharmacopoeias limits. The average

percentage deviation of 20 tablets of each formulation was maintained constant; the weight

variation of the tablets were within the permissible limits of 5%.Weight of the tablet was fixed at

300mg and the weight variation for every batch was tested and found within the acceptance

limits. The hardness of all batches ranged from 3-4 kg/cm2. (Table no. 5).Percentage friability

was below 1%. Friability test of all the formulations was found satisfactory showing enough

resistance to the mechanical shock and abrasion. (Table no 5).Drug content uniformity in all

formulations was calculated and the percent of active ingredient ranged from 98-102.

The in vitro dissolution study of F1, F2 and F3 were performed for 1hr time period. The

results indicated that F1 and F2 and F3 formulations were unable to control the release of drug

over 1hr time period. The results of dissolution studies of formulations F1, F2 and F3 were

shown in figure (12). The dissolution study for F4, F5 and F6 were performed for 1hr time

period. The F4 formulation containing PEG6000 and sorbitol releases 92% of drug in 45

minutes time period. F5 formulation consisting of PEG6000 and mannitol controls the drug

release for 1hr and 95% of drug is released in 45 minutes time period. F6 formulation

containing sorbitol was unable to control the drug release over 1 hr time period. The drug

release at 45 minutes was 78%. The results of dissolution studies of formulations F4, F5 and F6

were shown in figure (13). The dissolution study for F7 F8 and F9 were performed for 1hr time

period. F7 formulation containing sorbitol was unable to control the drug release over 1hr time

period. The drug release at 45 minutes was 87%.F8 formulation containing sorbitol higher in




concentration than in F7 formulation release 91% of drug in 45 minutes time period. F9

formulation consisting of copovidone and sorbitol was able to control the drug release and

releases 94% of the drug in 45 minutes time period. The results of dissolution studies of

formulations F7, F8 and F9 were shown in figure (14), F10 formulation consisting of PEG6000

and sorbitol was able to control the drug release and it releases 96% of drug at 45th

minute. So it

is considered as the optimized formulation as it shows better drug release than other

formulations. The results of dissolution studies formulation F10 were shown in the figure (15).

The dissolution profiles of optimized and marketed formulations were compared. From the

results it was confirmed that the optimized formulation (F10) showed better drug release i.e.

96% than marketed formulation which showed 86% drug release at the end of 45th

minute. The

results were shown in figure (16).

Kinetic modeling of drug release

The mechanism of release for the optimized formulation was determined by finding the R2

value

for each kinetic model viz. Zero-order and First-order. Thus from the resul ts it can be said

that the drug release follows Zero order kinetics.

CONCLUSION

The present work on enhancement of solubility of ritonavir tablets by solid dispersion technique

utilize PEG 6000, copovidone, sorbitol and mannitol to increase the solubility of the formulation

in 1hr time period. F10 formulation showed better drug release of 96% drug release at the end of

45th

minute compared to other formulations and marketed formulation. So F10 is the optimized

formulation. Among the polymers used the role of PEG6000, copovidone and sorbitol is

noteworthy in enhancing the solubility. Drug-excipients interaction was carried out for pure drug

and optimized formulations by using FTIR study. In this analysis drug – excipients compatibility

interactions were not observed. From the results obtained it was concluded that the optimized

formulation follows zero order release kinetics.

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