Optimization Of Dolutegravir Solid Dispersion To Enhance Its Solubility By 22 Factorial Designs

The majority of drugs on the market are designed for administration via the oral route; this is the most convenient method of drug delivery. The solubility of drug compounds in water is such an important issue in drug development. If a drug has poor oral bioavailability, methods to Improve its solubility are often considered first in an attempt to move compounds from BCS [2,4] Various methods were employed to enhance the solubility of class II drugs.[1,6,7.] Solid dispersion is one that is widely used to describe a system in which drug particles are homogeneously dispersed in a carrier matrix [1]  Factorial designs (FD, full or fractional), also known as experimental designs for the first-degree models, are the most popular response surface designs. In the present study we tried to enhance the solubility of Dolutegravir class-II using various polymers and different methods. The maximum solubility was enhanced using polymers Kollidan and Polaxmer-237. These two polymers were used to optimize the solid dispersion formulation by 22 factorial design using Design Expert® 12 software. The optimsed solid dispersion mixture was used to formulate tablets. We determined the Drug excipient incompatibility studies using TLC and FTIR. SEM photographs of Dolutegravir exhibited high crystallinity with several planes of surfaces. Polaxamer 237 exhibited a spherical shape of granular form of beads. Blend shows that the drug was adsorbed on to the spherical beads and there by enhanced the solubility of dolutegravir and reduces the crystallinity.

MATERIALS AND METHODS

Preformulation studies:

Phase Solubility: Phase solubility analysis is the quantitative determination of the purity of a substance through the application of precise solubility measurements. A 50 mg of dolutegravir drug was taken and it is solubilised in 50ml of phosphate buffer 6.8pH and the results were discussed in later section. Saturation Solubility Studies Dolutegravir solubility was determined by  shake-flask method. Plain dolutegravir in excess quantity was placed in separate glass stoppered flasks containing few ml of distilled water. The samples were placed on magnetic stirrer at 37? and 100 rpm until equilibrium was achieved (24 h). The aliquots were filtered through wattman No.41 filter paper. The filtrates were diluted appropriately in distilled water and assayed spectrophotometrically at 254 nm. The results were given in later section. 

Drug Excipient Compatibility Studies [3]

Study of drug-excipient compatibility is an important phase in the pre-formulation stage of drug development. The potential interactions between drugs and excipients have effects on the chemical, physical, bioavailability and stability of the dosage form. Drug-excipient compatibility studies to provide data for drug-excipient interaction which can further help in selection of excipient for the development of stable dosage form. It Includes TLC and FTIR studies

Thin Layer Chromatography (TLC):

A simple TLC technique is used in order to know the interaction between drug and excipients as a part of Preformulation studies. For this the pure drug, polymer and its combinations with the polymers were subjected to chromatographic studies.

TLC system

Precoated TLC plates:

Mfg. by S.d fine chemicals silica gel G 

Adsorbent Layer:

Mfg. by S.d fine chemicals silica gel G

Layer Thickness:

200µm, Separation Technique: Ascending, Size: 10 × 20cm

Mobile phase:

chloroform: Benzene: Methanol: Acetic acid 6: 3: 1: 0.1 Three spots were made on the TLC sheet   A .Drug:

Dolutegravir,   B. Excipient: Polaxmer -237,  C. Drug + Excipient

Amount applied: 

10µL, Detection: UV chamber. The results were given in later section.

Fourier-Transform Infrared Spectroscopy (FTIR):

It is used to identify the compatibility between drug and excipient. A common FTIR spectrometer consists of a source, interferometer, sample compartment, detector, amplifier, A/D convertor, and a computer. The results were given in later section

Preparation Of Solid Dispersion:

Solid dispersion of dolutegravir with ?-cyclodextrin, kollidon, Soluplus polaxamers 188, 237 and 408 were prepared in the ratios of 1:1, 1:2, 1:3 of drug-carrier. Physical mixture techniques have been used for the preparation of solid dispersion in the present study. In this method, 10mg, dolutegravir was accurately weighed and mixed thoroughly; physical mixtures were formulated by mixing drug and carrier in geometric proportions using a spatula without applying pressure. The solid dispersions were passed th

rough a No. 60 sieve and stored over anhydrous calcium chloride in a desiccator. Six polymers were used to test the solubility (Total 18 formulations).  Out of six polymers two were found to be better. By considering  those two polymers few more methods like solvent evaporation method and micro-oven method were employed. F8 and F14 formulations are subjected to solvent evaporation and micro oven method).

F19 formulation formulated using drug and polaxmer-237 (1:2) has shown better solubility of the drug among all. This formulation was selected for dosage form development. Combinations of Kollidon and Polaxmer- 237 were used for optimization studies using DOE version12. In-vitro dissolution testing methodologies can be used to determine the key factors that influence the performance of a drug. 900ml of required buffer was placed into dissolution beaker and switch on the dissolution apparatus. The following conditions are maintained  Bath and bowl temperature- 37ºC. Buffer – 900ml, Stirrer rotation speed – 50rpm When these conditions are reached the tablet was placed in the dissolution medium. Sampling was done properly. i.e., 5ml of sample is withdrawn from the medium with specified time interval (15/30min) for testing and 5ml buffer is replaced to the medium. The withdrawn sample is tested for absorbance in  UV spectrophotometer and results were discussed in later  section.

Apparatus: Lab India DS8000,

Rpm: 50 rpm,

Medium: 6.8 pH phosphate buffer

Volume: 900 ml,

Temperature: 37? ± .5?

Scanning Electron Microscope (SEM) analysis [5]

Electron micrographs for solid dispersion of Dolutegravir and polaxamer 237 in 1:2 ratio was obtained using scanning electron microscope (SEM; Joel JSM-5910, Japan) operating at 10 kV.. To study themorphology of solid dispersion of Dolutegravir and polaxamer 237 micrographs with different magnification were obtained and results were discussed in later section.

Factorial Design [11]

Optimization helps in determining the dependent and independent factors and how they exert their effect on the characteristics of the formulation. Four formulations were optimised using design expert software 12.0. Optimized formulation was selected based on Statistical analysis. The study was carried out to design an optimised formulation of dolutegravir solid dispersion using a blend of two solubility enhancers- Kollidon and polaxamer 237. Two independent variables (kollidon and polaxamer 237) and two levels were set as high and low. The study was designed to be a 22 fractional design, meaning that two variables were studied at two different levels

Formulation  and Evaluation Of Dolutegravir Immediate Release Tablets:

The tablets were prepared by direct compression method. In this method, tablet ingredients were accurately weighed and formulated in to tablets.  Dolutegravir, polaxamer 237, MCC, starch, magnesium stearate and finally talc were added and mix thoroughly and passed through sieve 44 and mixed with lubricant and glidant evenly. The blend was compressed using single punch tablet machine.

Pre-compression studies:

Angle of Repose, Determination of Bulk Density and Tapped Density, Compressibility Index (Carr’s Index) and  Hausner’s Ratio:

Post-compression studies:

Thickness, hardness, Weight variation Friability Test, Drug Content, In -Vitro Drug Release studies.

Stability Studies:

The formulated tablets were stored at room temperature for a period of 3 months. The stability of dosage form was examined at regular intervals and results were discussed in the later section.

RESULTS AND DISCUSSION:

Solubility:

Slightly soluble in water and methanol.

0.095mg/ml in water

Phase Solubility:

Table No: 8.    Phase solubility of dolutegravir

Melting point:190-193?

Fourier Transform Infrared Spectroscopy (FTIR): It is a technique used to obtain an infrared spectrum of absorption or emission of a solid, liquid or gas.

1. The pure drug dolutegravirexhibited sharp peak at 2234.96 cm?1,1393.32 cm?1, 856.65 cm?1, and 885.53 cm?1 indicating the presence of C-N stretching, C?C stretching, C-O-C stretching, C-H bending, and Ar-H bending.(Fig 4.1)
2. For Poloxamer 237 sharp peaks at 2237.60 cm?1, 2165.00 cm?1, and 842.24 cm?1 indicated C-N stretching, C?C stretching, and C-H bending. (Fig 4.2)
3. For dolutegravir and polaxamer 237 solid dispersion, sharp peaks at 2237.12 cm?1, 2165.40 cm?1, 1391.18 cm?1, and 842.24 cm?1 indicated C-N stretching, C?C stretching, C-O-C stretching, and Ar-H bending. (Fig 4.3)

The standard Rf value ofis Dolutegravir 0.77 cm according to Literature. The Rf value of pure drug and drug in combination of excipients is 0.71 and 0.74cm.   Very slight deviation in second decimal was observed. This indicates the compatibility of drug and excipients. This is a qualitative index for drug excipient compatibility studies.

Note:

The studies reported that there is no incompatibility between drug and excipients, So we proceed further to experimental work.

 F14 is considered for further studies.

1. SEM photographs of dolutegravir exhibited high crystallinity with several planes of surfaces.
2. Polaxamer 237 exhibited a spherical shape of granular form of beads.
3. Blend shows that the drug was adsorbed on to the spherical beads and there by enhanced the solubility of dolutegravir and reduces the crystallinity.
4. The size of the particles were found to be 10µ

2²factorial Design:

For interaction effect, KOLLIDON AND POLAXAMER-237 is used

Factor coding is Coded..Sum of squares is Type III – Partial. The Model F-value of 84.55 implies the model is significant. There is only a 0.21% chance that an F-value this large could occur due to noise. P-values less than 0.0500 indicate model terms are significant. In this case A, B, AB are significant model terms. Values greater than 0.1000 indicate the model terms are not significant. If there are many insignificant model terms (not counting those required to support hierarchy), model reduction may improve your model

The Interaction between Kollidone-20mg and Poloxamer- 237 -20 mg would give dissolution of 36.5% at 1hr52.8% in 2 hrs and 80.0% in 3hr The Desirability value (should be close to 1) of 1.00 shows that it is highly likely of the most desirable result to have. Note:  The simplest model which we have selected for optimization of various ratios of the polymers was found to be significant statistically.