Solubility enhancement and tablet formulation of Ritonavir  

J.J. Naik *

JES’s College of Pharmacy, Nandurbar, Dist Nandurbar, MS, India.

*Correspondence: naikjayu91@gmail.com

 

Article Information		Abstract
Research Article Received: 22/03/2024 Revised  : 30/03/2024 Accepted: 05/04/2024 Published:30/04/2024   Keywords Ritonavir, Excipients, Ball mill, Tablet, Solubility enhancement.		The aim of this study was to prepare and evaluate Ritonavir for enhancing the dissolution rate and Bioavailability several methods and newer emerging technologies have been developed. For the solubility enhancement of ritonavir solid dispersion, complexation, particle size reduction method was used. Solubility enhancement method which showing the best result after evaluation of parameter was selected for preparation of immediate release tablet of ritonavir by using appropriate excipients. Particle size reduction method was selected for the formulation of tablets. The physical state of the ritonavir drug and excipients was characterized by differential scanning calorimetry, powder X-ray diffraction, and U.V spectroscopy. Ritonavir drug were formulated into tablet by direct compression method. On comparing with pure drug and formulated tablet, the dissolution of Ritonavir was enhanced dramatically. Formulation showed faster drug release. The experiment was conclusively indicated that the use of particle size reduction method by using water soluble carriers improved the solubility of Ritonavir.

 

INTRODUCTION

Poor solubility is one of the most common problems in the world of pharmaceutics, and this is universally acknowledged. When taken orally, drugs that are poorly water soluble frequently exhibit low bioavailability since intestinal absorption of the medication is frequently a rate-limiting step. Therefore, improving the solubility rate of this kind of medicine is crucial [2].  According to the biopharmaceutical classification system (BCS), many current medications fall into the Class II group, which is distinguished by poor solubility and high permeability [1]. Anti-retroviral medication ritonavir, which is frequently administered, is classified as a Class II medicine under the "BCS" system and has a poor oral bioavailability because of its insufficient aqueous solubility. In water and other aqueous solutions, ritonavir is virtually insoluble. Ritonavir needs to improve its oral bioavailability, solubility, and dissolution rate [9].  Several methods have been used to increase the solubility, dissolution rate, and bioavailability of poorly soluble medicines, including solid dispersion, cyclodextrin complexation, use of surfactants and solubilizers, and particle size reduction. Particle size reduction is one method among many for improving the solubility, dissolving rate, and bioavailability of poorly soluble medicines. It is a straightforward, industrially useful method [4]. The goal of the current research project was to create ritonavir tablets with a particle size reduction approach to increase solubility and dissolving [4].

MATERIALS

Ritonavir was provided as a gift sample by Lupin Pharma in Pune, Sourav Scientific Trades in Pune, Mahindra's Pure Chemical Laboratory in Pune, Analab Fine Chemical in Mumbai, Bhortek Chemical in Pune, and Analytical Laboratory. The investigation only employed analytical-grade compounds.

METHODS

1)  Solid dispersion method:

Since solid dispersion may be used in so many different applications, it is the subject of several investigations. They can serve as the foundation for a product used for a variety of delivery methods and dosage forms, including the most often used dosage form, the tablet. A hydrophilic matrix and a hydrophobic medication are the two different components that make up a range of solid products known as solid dispersion. Sorbitol and polyethylene glycols (PEGs) are the two hydrophilic carriers for solid dispersions that are most frequently utilized. This was utilized for developing the solid dispersion method. Solid dispersions are an effective pharmaceutical approach for boosting the drug dosage forms' ability to dissolve, absorb, and provide therapeutic benefit. There are many ways to prepare the solid dispersion to increase aqueous solubility, some of which are listed below [8]^.

a) Solvent Evaporation Method:

In the solvent evaporation approach, the medication and carrier were both dissolved in a typical organic solvent before the solvent was either evaporated under vacuum or at a high temperature to form a solid result. In this procedure, 200 mg of Sorbitol was dissolved in 10% ethanol. Ritonavir 50 mg was dissolved in a 2:3 mixture of water and ethanol. The medication solution was supplemented with Sorbitol solution [8]. Water caused the drug to precipitate, therefore extra ethanol (0.5 ml) was added to the mixture to clean it up. This transparent solution underwent a 30-minute vortex process. It was then vacuum dried or left at room temperature until a solid result was created [10].

b) Melting method

The fusion method is another name for the melting technique. Heat was present as the preparation was being done. After being allowed to cool at room temperature until a solid product was produced, the carrier and other active component melt together in a china dish [11]. This procedure involved melting 200 mg of Sorbitol at 120°C in a china dish, adding 50 mg of the medication, and mixing for 20 minutes. After then, it was allowed to cool at normal temperature until a solid product developed. [5]

 

 

c) Co-grinding method

Using a mortar and pestle at room temperature, the medication and the carrier are combined with the solvent for 10-15 minutes, or until the solvent evaporates. In this procedure, the medication was triturated in a mortar and pestle with a small amount of methanol until it was dissolved. At room temperature, the carrier was added, and the suspension was quickly triturated until the solvent evaporated and a solid product developed [5].

2) Cyclodextrin complexation:

Cyclodextrin complexation resembles a host-guest situation. Cyclodextrin serves as the host molecule in this interaction, and the drug molecule that will be trapped in the host cavity serves as the guest molecule. Different non-covalent forces, such as Vander walls forces, hydrophobic contact, and dipole movement, are in charge of complex formation with cyclodextrin. Most often, the cavity only contains one guest molecule at a time. More than one cyclodextrin molecule can bind to the visitor in the case of high molecular weight compounds [12]. Cyclodextrin can combine with medicinal molecules to produce complexes that enhance a medication's solubility, dissolving rate, bioavailability, and stability. The goal of the current complexation work with CD was to increase the solubility and rate of dissolution of ritonavir [6].

 Preparation method:

0.02, 0.04, 0.08, 0.10, and 0.12 molar solutions of -cyclodextrin were created for the formation of the drugs with cyclodextrin complex. Drug was added to a molar solution and allowed to sit in a volumetric flask before being shaken for two hours. The solution was filtered after shaking or stirring. The absorbance of each solution was then measured using UV spectroscopy. The chart was drawn. After the drug's solubility and stability constants were determined [6].

3) Particle size reduction method:

 Drug particle size affects a drug's solubility; as a particle gets smaller, its surface area to volume ratio rises. Greater contact with the solvent is made possible by the larger surface area, increasing solubility. Solubility improvement through particle size reduction is a productive, repeatable, and affordable technique [13]. One of the common methods for reducing particle size is micronization. The micronization process does not increase equilibrium solubility; instead, it increases the rate at which pharmaceuticals dissolve by increasing their surface area. These methods increase drug surface area and speed up drug dissolution by reducing the size of drug particle. Drugs are micronized using milling methods such as ball mills or mill [4].

a) Ball milling:

The pharmaceutical ball mill is typically a cylindrical device that rotates around a horizontal axis to grind therapeutic powders. The grinding medium, which is often ceramic balls, flint pebbles, or stainless steel balls, is partially inserted into the device together with the material to be processed [12]. Since the amorphous form of a drug is more easily soluble than the crystalline form of a drug, the ball milling technique for size reduction is vital to creating amorphous powders of drugs that promote dissolution of drugs. This process is an essential way to increase the solubility of drugs that aren't very water soluble [4].

EVALUATION

A) Analysis of Ritonavir:

1. Description:

Ritonavir drug sample's physical characteristics and powder nature were examined.

 2. Melting point:

By using the capillary method, the melting point of ritonavir was determined.

 3. Solubility:

Various solvents were used to determine ritonavir solubility.

 4. Infra-red spectrum:

Ritonavir IR absorption spectra was recorded using the potassium bromide pellet technique. A uniformly blended dry sample of the drug and potassium bromide was formed into a pellet, and an IR spectrum was acquired using an FTIR spectrometer. The drug's final spectrum was compared to the ritonavir reference spectrum.

 5. U.V spectroscopy:

A 10 ml volumetric flask was filled with 10 mg of the drug after it had been accurately weighed. 10 ml of methanol were used to dissolve the drug. As a result, a ritonavir stock solution containing 1000 g/ml was formed. Methanol was used to dilute the solution, resulting in a 100 g/ml solution. The UV spectrum was identified between 200 and 400 nm. After the identification of the maximum absorption wavelength (max) by the scan, the calibration curve was further prepared at the identified wavelength of maximum absorption (max).

6. Powder X-ray diffractometry (PXRD):

A powder X-ray diffractometer was used for the diffraction studies. To decrease the effect of orientation, the sample was rotated during data collection. Pure drug, solid complex PXRD pattern recorded between 2=5 to 50o at 40KV and 30 mA.

7. Differential scanning calorimetry (DSC):

One of the most used methods for examining how drugs interact is differential scanning calorimetry. Pure drug samples were placed in flat-bottomed aluminium pans and heated between 25-300ᵒC at constant rate of 10ᵒ/min by employing alumina as the reference standard and nitrogen purging in a differential scanning calorimeter.

8. Preparation of standard curve of ritonavir:

1. 10 ml volumetric flask was filled with precisely weighed 10 mg of the drug. As a result, a ritonavir stock solution containing 1000 g/ml was obtained.

2. Methanol was used to dilute the solution, resulting in a 100 g/ml solution.

3. To prepare the drug solution, the proper portions (0.5–2.5) of the standard solution were taken in a 10 ml volumetric flask and diluted with methanol.

4. At a maximum wavelength of 239 nm, the absorbance of each standard solution was measured.

Evaluation of Particle size reduction method:

a) An increase in percentage yield (%) solubility

b) Bulk density

The mass of the powder divided by the bulk volume is known as bulk density. The sample's bulk density was calculated by gently pouring 5g of the sample through a glass funnel into a graduated cylinder with a volume of 50ml. It was recorded how much space the sample took up. Following is how the bulk density was determined:

Bulk density

c) Tapped density:

A glass funnel was used to gently pour 5 g of sample into a graduated cylinder with a volume of 50 ml. A consistent volume was attained by tapping the cylinder at a height of 2 inches. Following the recording of the sample's post-tapping volume, the tapped density was determined as follows:

Tapped density

d) Compressibility index

Compressibility is the easiest way to determine the free flow of powder. Compressibility index  (I), which is calculated as follows, provides an indication of how easily material may be made to flow.

Compressibility index=

e) Haussner’s ratio:

This measures the ease of powder flow in an indirect manner. The following formula is used to calculate it: Haussners ratio=

Lower Haussners ratio (  indicates better flow properties than higher ones (

Formulation of tablets:

Ritonavir immediate release tablets were prepared using the solubility enhancement technique that, resulting from evaluation parameter, produced the best results employing appropriate excipients. The method of particle size reduction was chosen for the tablet formulation. The ritonavir drug was contained in a tablet together with talc, lactose, polyvinylpyrrolidone, starch, etc. The components were thoroughly combined. The tablet compression machine compressed the powder. Tablets were maintained at a consistent weight. The rotary tablet machine was used to prepare all of the tablets using the direct compression method.

Evaluation of tablet:

a. General appearance

The general appearance of a tablet, which is essential to customer acceptance. Included are the tablet's size, shape, color, scent, texture, and other physical defects.

b. Tablet thickness

Tablet thickness is an important factor in both duplicating appearance and counting with filling machinery. The uniform thickness of the tablets is used as a counting mechanism by some filling equipment. A micrometer was used to measure the thickness of ten tablets. Dimensionally, the tablet's size may be characterized, observed, and controlled.

 c. Uniformity of weight

Twenty tablets were taken and their weights were calculated individually and collectively on a digital weighing balance in accordance with USP method for uniformity of weight. The total weight was used to calculate the average weight of one tablet. The weight variation test would provide a reliable way to evaluate the uniformity of the drug content.

 d. Disintegration time

Six tablets were subjected to the test using the equipment recommended by USP. The time it took for the tablet to completely disintegrate, leaving no palpable bulk inside the instrument, using either distilled water or (0.1N HCL) as a disintegration media was recorded.

 e. Friability

It measures the tablet's mechanical strength. The following approach was done to determine the friability using the Roche friabilator:

Tablets that had been preweighed were put in the friabilator. With each turn, the plastic chamber of the friabilator, which rotates at 25 rpm, drops the tablets six inches away. The tablets rotate in the friabilator for at least 4 minutes. When the test is complete, the tablets are dusted and reweighed; the weight loss indicates the percentage of friability.

% Friability=loss in weight/Initial weight 100

Or friability = 100

f. Tablet hardness

The force needed to break a tablet across its diameter is referred to as the tablet's hardness. The hardness of the tablet affects how resistant it is to handling and storage conditions that could cause chipping, abrasion, or breaking.

 g. Dissolution studies

Using USP type II equipment, in vitro dissolution experiments of immediate release tablets were carried out.

Test conditions such as 900 ml of dissolving medium, 50 rpm, -37.0 0.5ᵒC, of dissolution medium, and 0.1N HCL as the dissolution medium.

Procedure: The apparatus was operated while maintaining the previously mentioned conditions with the tablets in the dissolution media. 5 ml samples were taken out 5, 10, 15, 20, 30, 45, and 60 minutes apart. Every time, the bulk was supplemented with an identical volume of brand-new dissolving medium that was kept at the same temperature. Samples were run through Whatman filter paper, and absorbances at 239 nm were measured. At each time point, the percentage amount of drug release was computed.

 h. Stability testing:

According to the ICH standards for accelerated studies, stability testing of the tablet and excipients was performed under the specified conditions for the duration of the study.

 i) 30 C and RH 65%  5%

ii) 40 2 C and RH 75% 5%

After being characterized over a period of 7, 14, days, 1, 2, and 3 months, the Tablet and excipients were discontinued.

I. Infrared spectroscopy

KBr discs were used in an IR analysis. the formulation standard in comparison to the reference standard.

RESULT AND DISCUSSION

Analysis of ritonavir:

A. Description: Visual inspection showed that it is white hygroscopic powder.

B. Melting point:The melting point of ritonavir was found to 123̊C (120̊ C-125̊ C).

C. Solubility: Ritonavir is easily soluble in methanol and ethanol but insoluble in water.

D. Infra-red spectrum: The IR spectrum of ritonavir and its interpretation shown in figure 1 and table 1. Which confirm sample is ritonavir.

Figure 1: IR spectrum of ritonavir

Table 1: Interpretation of IR spectrum of ritonavir

2) U.V. spectroscopy:

Table 2. Calibration curve of ritonavir drug:

 

Figure 2: Calibration curve of ritonavir in methanol.

A solution of ritonavir in methanol showed maximum absorption at 239 nm (λ_max). Calibration curve was a straight line. The absorbance increased with the increase in concentration. Thus the standard curve followed the Beers-Lamberts law.

3) Powder X-ray diffractometry (PXRD):

Figure 3: Powder X-ray diffractometry (PXRD) of ritonavir drug

In powder X-ray diffractometry (PXRD) evaluation method, drug shows sharp peak. This peak shows that drug does not undergo any polymorphic change.  Hence, it was concluded that the drug was amorphous in nature.

G. Differential scanning calorimetry (DSC):

Figure 4: Differential scanning calorimetry (DSC) of ritonavir drug

The differential scanning calorimetry thermogram of pure drug ritonavir shows an endothermic peak at 123.63̊C corresponding to its melting point. This was indicate absence of interaction in drug.

Evaluation of solubility enhancement method

Particle size reduction method:

a) Table no.3. % Solubility increased by particle size reduction method.

As the particle size was reduced, solubility of drug was increased.

Particle size reduction was most convenient, reproducible, economic, and suitable method for the formulation of immediate release tablet. Particle size reduction method was selected for the formulation of immediate release tablet of ritonavir.

b) Bulk density: It was calculated by following formula,

Bulk density

1) Bulk density of pure drug: 0.80gm/ml

2) Bulk density of tablet mixture: 0.9027gm/ml

c) Tapped density: It was calculated by following formula

Tapped density

1) Tapped density of pure drug: 1.016gm/ml

2) Tapped density of tablet mixture: 1.083gm/ml

d) Compressibility index: It was calculated by following formula

  Compressibility index=

1) Compressibility index of pure drug: 21.25%

2) Compressibility index of tablet mixture: 16.6%

e) Haussner’s ratio:

It is calculated by the following formula,

Haussners ratio=

Lower Haussners ratio (  indicates better flow properties than higher ones (

1) Haussners ratio of pure drug: 1.27

2) Haussners ratio of tablet mixture: 1.19

f) Angle of repose: It is calculated by the following formula, tanⱷ=h/r

1) For pure drug: 24.98%

2) For tablet mixture: 24.49

Characterisation:

a) Pure drug:

Figure 5: characterisation of pure drug by using IR spectrum which analyzed stability.

b) Tablet mixture:

Figure 6: characterisation of Tablet mixture by using IR spectrum which analyzed stability.

Evaluation of tablet

a. General appearance:

i) Colour: white

ii) Odour: fruity breath odour.

iii) Taste: bitter metallic

iv) Size and shape: It was 350mg tablet which have rounded shape.

b. Tablet thickness: Tablets thickness was recorded using micrometer.

To evaluation of tablet thickness there was 20 tablets used

Table 4: Tablet thickness

Average thickness of ritonavir=58/20=2.9mm. (Tablet thickness was 2.9mm)

Uniformity of weight or weight variation test:

Table 5: Weight variation test

Average weight = 6.976/20 = 348mg.

Table 6: Disintegration time:

Friability:

Table 7: Friability of ritonavir

Table no.7. Shows 0.97% friability of ritonavir.

Tablet hardness:

Table 8: Tablet hardness

Table no.8. Shows Tablet hardness 4.83 kg/cm.²

Drug content: Drug content of ritonavir was found about 99.8%

Dissolution studies:

Table 9: In-vitro drug release profile of ritonavir tablet

Figure 7. Shows 100.026 % drug release of ritonavir tablet

Compatibility studies:

Stability testing of tablet and excipients carried out under following condition for period as prescribed by ICH guidelines for accelerated studies.

i) 30 C and RH 65%  5%

ii) 40 2 C and RH 75% 5%

The Tablet and excipients was withdrawn after a period of 7, 14, days, 1, 2, 3, month analyzed characterisation.

Table 10: Compatibility studies of drug with excipients

DSC of ritonavir tablet:

Figure 8. The differential scanning calorimetry thermogram of ritonavir tablet shows an endothermic peak at 122.17ºC corresponding to its melting point. This was indicate absence of interaction in drug

PXRD of ritonavir tablet:

Figure 9: In powder X-ray diffractometry (PXRD) evaluation method,

Tablet mixture shows sharp peak. This peak shows that Tablet mixture does not undergo any polymorphic change.  Hence, it was concluded that the Tablet mixture was amorphous in nature.

CONCLUSION

Present work was to enhance the solubility and tablet formulation of ritonavir. It was concluded that ritonavir tablets formulated employing its particle size reduction method gave rapid and higher dissolution rate when compared to plain drug. Particle size reduction method of ritonavir prepared immediate release tablet by employing carrier like PVP, starch. Lactose, talc, magnesium stearate etc.  This particle size reduction method could be formulated into compressed tablets retaining their fast dissolution characteristics and fulfilling official (I.P.) standards.

ACKNOWLEDGMENTS

The authors are thankful to the chairman, management and principal of JES’s college of Pharmacy, Nandurbar for providing the suitable facility to conduct the present work.

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