Solubility Enhancement, Formulation and Evaluation of Dolutegravir

Solubility phenomena have great influence on pharmaceutical industry1. It is defined as dissolution of solute in solvent to give a homogeneous system2. The solubility of substance basically depends on the temperature, pressure and existence of other chemicals of the solution and also chemical and physical properties of solute3,4. Solubility take place under equilibrium, which means solubility, obtain from the simultaneous and diverging process of dissolution and phase joining5. Because of certain condition solubility may increases which give a supersaturated solution. IUPAC defined solubility; it is the analytical composition of a saturated solution expressed as a fraction of solute in a designated solvent. It may be asserted in units of molality, mole ratio and concentration6,7. It is applied to all areas of chemistry, organic, inorganic physical and biochemistry. In all areas it will depend on the important physical condition that is concentration, temperature and pressure and also enthalpy and entropy that are directly related to the solvents and solute. Solubility behavior of drugs in solvent is important because solvent blends are often used in preformulation and drug formulation. Also, it is important to obtained desired concentration of the drug in systemic circulation, to attain maximum utilityin newly developed drug and to increase the therapeutic effectiveness8,9. Solubility of drug substance can be changed by two ways, either through formulation approaches or through material engineering10. Active pharmaceutical ingredient with poor aqueous solubility is one of the major obstacles in formulation development of oral dosage form. Because of this reason solubility is on the utmost point of formulation scientist. The solubility of drug is essential factor in determining the rate and extent of absorption. More than 90% of drugs are taken orally. Drug absorption, bioavailability, pharmacokinetic profile of orally taken drug, these factors is highly reliant on solubility of that compound in water11. About 90% of drugs approved since 1995 exhibit poor solubility. Nearly 40% of new chemical entities identified in combinatorial screening programs used by many pharmaceutical companies are practically insoluble in water and not well absorbed when taken orally, which affect dissolution rate and bioavailability, resulting in high intra and inter subject variability and lack of dose proportionality12. Only 8% of new drugs in the world possess high solubility and permeability13. Poor water solubility obstructs drug bioavailability and decreases its pharmaceutical development. Pharmaceutical development of drug with low water solubility requires creation of appropriate formulation with various techniques14. Lack of solubility is the most rate-limiting step in the process of oral drug absorption; therefore, there is need to increase the solubility of drug. The Noyes- Whitney equation gives relation between solubility and dissolution, an increase in dissolution gives a significant enhance in solubility15,16. For this reason, the drug entities are grouped into four classes which are mainly based on solubility and permeability and this categorization are called as Biopharmaceutical Classification System (BCS). G.L. Amidon invent this classification in 1995 and since then it has become a yardstick in the bioequivalence regulation of oral drug products17,18.

Biopharmaceutical classification system of drug

The Biopharmaceutical Classification System (BCS) is a scientific structure for categorizing drug moieties according on their aqueous solubility and intestinal permeability). The BCS plays vital role for formulation scientist, for advising strategy to increase the effectiveness of drug development by proper choice of dosage form and bioequivalence tests19,20. The BCS guidance depends on three major factors, solubility intestinal permeability and dissolution, which govern the rate and extent of drug absorption21,22. Solubility of the drug substance will not be principal parameter when the absorption of the drug substance is permeation rate limited and so that in vitro dissolution study can be used to express bioavailability or bioequivalence of the drug product through in vitro-in vivo correlation. BCS gives better understanding of the connection between drug release from the product and the absorption process. According to this, the rate limiting step has prime importance. If drug release or dissolution is rate limiting process, then the bioavailability will be influence only by the in vivo performance of dosage form. On the contrary, as long as the penetration through bio-membranes is a restricted course, bioavailability and bioequivalence are not so reliant upon the release of drug behavior of the dosage form23,24.

MATERIAL & METHOD:

Table .1: List of drug, excipients and chemicals:

Table .2: List of Instruments/ Equipment:

EXPERIMENTAL WORK

Preformulation study

Organoleptic properties:

The sample of Dolutegravir was studied for organoleptic properties such as colour, odour, and appearance. The results are shown in Table

Melting point:

The melting point if the drug was determined by open capillary method using the melting point apparatus. The drug sample was filled into capillary tube which was previously sealed at the end. The tube was then placed in melting point apparatus. Temperature at which sample started melting and the temperature at which it completely melt was noted. The melting point is reported in Table Solubility: Solubility of Dolutegravir was determined in water, methanol, 0.1N HCI, pH6.8 Buffer and DMSO. The solubility was determined by addition of known quantity of drug to 2 ml of solvent each time until saturation. Solubility is determined on the basis of per ml dissolved sample. Results of solubility are shown in Table

Ultraviolet spectroscopy:

A) Calibration curve in Methanol:

Accurately weighed 10 mg of drug was transferred to calibrated 100 mL volumetric flask. It was dissolved in 20 mL methanol by sonication for 10 minutes. Final volume was made up to 100 mL with methanol to give the solution containing 100 μg/mL. From working standard solution, by pipetting out 5-25 μg/mL solution respectively into separate 10ml volumetric flask and diluting to volume with methanol to produce the concentration. The above solutions were scanned over the range of 400 nm to 200nm against blank (methanol). λ max was recorded and the absorbance of all solution was measured. The calibration curve was constructed by plotting concentration (5-25μg/mL v/s absorbance at λ max). Results shown in the Table

FTIR spectroscopy:

Infrared spectrophotometry is a useful analytical technique utilized to check the chemical interaction between the drug and other excipients used in the formulation. The sample (1 mg) was powdered and mixed with 10 mg of dry powdered potassium bromide. The powdered mixture was taken in a sample and the spectrum was recorded by scanning in the wavelength region of 4000-400 cm-1 using FTIR spectrophotometer Shimadzu(8400S). The IR spectra obtained is represented in Fig. No. and peaks values are mentioned in Table

Compatibility Studies:

To determine the compatibility of drug with excipients, drug-excipient compatibility study was carried out. Drug and excipient in 1:1% W/W were filled in the prewashed and dried amber colored glass vials and sealed with Aluminum cap. The sealed vials were kept at 40± 2°C for 1 day in oven. At the end of one day vials were removed from desiccator and were compared with control samples which were kept at room temperature. The control and test samples were examined. They were examined by FTIR method to study any interactions that may occur between drug and excipient. Peaks observed are shown in Figure.

Solubility Enhancement by Inclusion Complexation

Preparation of Inclusion Complexes:

For the preparation of binary inclusion complexes of Dolutegravir various technique like kneading method and various excipient. Polymer ratio was prepared out of which kneading method and β-Cyclodextrins were optimized as it gives better result than others.

Kneading Method:

Inclusion complex of Dolutegravir and Beta cyclodextrins were prepared by kneading method. In which distilled water was used to prepare drug: carrier complex in a mortar by grinding ingredients for half an hour. After grinding, the wet mass left to air dry at room temperature for 48 hours with intermit tent mixing and agitation. The complexes were made in different ratios with respect to drug and carriers.

Table 3: Formulation of Inclusion complex of dolutegravir and Beta cyclodextrin by Kneading method

Characterization of each Approach:

Production Yield:

The Percentage yield of complexes of various combinations was calculated using the weight of final product after drying with respect to the initial total weight of the drug and carrier used for the preparation of complexes. Percent production yields were calculated as per the formula given below. Table

PY: Product yield

PY =WO/WT × 100

WO: Practical mass (complexes)

WT: Theoretical mass (carrier + drug)

Drug content:

About 10 mg drug equivalent of complexes (theoretical) were weighed accurately and transferred to 100 ml volumetric flask to which 20 ml methanol was added and sonicated for 15 min. Final volume was made up with methanol to give 100 ppm ck solution. From this stock solution (100 ml), 1 ml was withdrawn and further diluted up to 10 ml with method solution was used for the assay for dray content by UV spectrophotometer at Concentration of drug in stock solution was calculated by using calibration curve and form which percent drug content was calculated, Table

% Drug Content = WA/WT × 100

WA: actual drug content: WT: theoretical drug content.

Method of preparation and evaluation of powder blend

Table No. 4 Formula for immediate release Tablet