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Influence of Darunavir: β-Cyclodextrin Complex on the Solubility of Darunavir

Ana Carolina Kogawa*, Josilene Chaves Ruela Corrêand Hérida Regina Nunes Salgado

Department of Pharmaceutics, School of Pharmaceutical Sciences ofraraquara, Universidade Estadual Paulista “Júlio de Mesquita Filho” - UNESP,raraquara, São Paulo, Brazil.

*Corresponding Author:
Ana Carolina Kogawa, Department of Pharmaceutics, School of Pharmaceutical Sciences ofraraquara, Universidade Estadual Paulista “Júlio de Mesquita Filho” - UNESP,raraquara, São Paulo, Brazil
Phone:
+55 16 3301 4681, Fax: +55 16 3301 6967

Received date: 15/09/2014 Revised date: 22/09/2014 Accepted date: 29/09/2014

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Abstract

Darunavir, a protease inhibitor used in the treatment of HIV infection, was complexed with β-cyclodextrin because of its low solubility in water and poor bioavailability, with the objective of improving the solubility of darunavir aiming subsequently the administration of lower doses and increasing patient adherence to the treatment. Children under seven are usually unable to swallow the solid medications, especially tablets 300, 400 or 600 mg, such as darunavir. To make adult medicines suitable for children, tablets or capsules are often processed to adjust dosages and facilitate swallowing, but in most cases they do not support the medication. Therefore, complexation developed is extremely interesting. The last World Health Assembly launched the global campaign „Make medicines child size‟. The determination of the solubility of drugs is a fundamental part in Biopharmaceutics Classification System. In this research purified water with pH 8.0, acetate buffer 0.05 M pH 4.5, phosphate buffer 0.2 M pH 6.8 and phosphate butter 0.05 M with 0.5 % Tween pH 3.0 were evaluated in the solubility of darunavir:β-cyclodextrin complex. In all dissolution media tested complex showed solubility at least 5 times greater than the free drug.

Keywords

Biopharmaceutics Classification System, child size, darunavir:β-cyclodextrin, solubility.

Introduction

Darunavir (Figure 1), protease inhibitor used in the treatment of HIV infection, has low solubility in waternd poor bioavailability, therefore it requiresdministration in relatively high doses in order to exhibit therapeutic efficacy [1-2].

pharmacology-toxicological-studies-Chemical-structure-darunavir

Figure 1: Chemical structure of darunavir (CAS 206361-99-1).

The important characteristics of molecule that needs to be considered essential fornti-HIV effectsre solubility, the extent to which molecule of solid is released from the surface by dissolution [3],nd stability in biological fluids. When these propertiesre unfavorable for some specific drugs, the formulationnd processinglternatives can be employed tochieve the maximum therapeutic gain [4].

The dissolution refers to the process by which drug moleculesre released from the solid phasend enter the solution phase that is dependent on the time that represents the final step in the release of thective substance [5]. The drug release from the dosage form depends on the drug solubility characteristicss wells the formulation componentsnd manufactory process.

The solubility of drug depends on its molecular propertiesnd itsbility to form hydrogen bonds with water molecules. Factors suchs pKa, pH, polymorphism, particle size, dosage form, excipients, manufacturing processes, intestinal transit, motility, volumend composition of intestinal fluidsffect the solubility of the drugs.

According to the FDA [6], the solubility of drug is determined by dissolving the higher dose ofn immediate release dosage form in the volume of 250 ml, or less, of buffer solution present in the range of pH 1.0 to 7.5t temperature of 37 °C.

The test of solubility of drug must be performed by the methods of equilibrium, potentiometric or intrinsic dissolution. The equilibrium method is the most used, in which the saturation concentration of the drug, the speednd time ofgitationre fundamental [6].

The solubility is parameter used for the classification of drugsccording to the Biopharmaceutics Classification System (BCS),s wells the intestinal permeability of the drug. Nowadays the BCS becamen important tool for the development of formulations.

Darunavir: β-cyclodextrin complex (Figure 2) was carried out with the objective of improving the solubility of darunaviriming subsequently thedministration of lower dosesnd increasing patientdherence to the treatment [2]. Because using smaller doses thedverse drug reactionsnd drug interactionsssociated withntiretroviral therapy can be decreased. It is worth remembering that in chronic treatments even moderate toxicity can lead to serious complications [4].

pharmacology-toxicological-studies-Darunavir-cyclodextrin-cluster

Figure 2: Darunavir: β-cyclodextrin complex, cluster-b.

Children under sevenre usually unable to swallow the solid medications, especially high strength dosess 300, 400 or 600 mg, commonly doses for darunavir. To makedult medicines suitable for children, tablets or capsulesre often processed todjust dosagesnd facilitate swallowing. However, liquid formulations, essential for pediatric pharmacotherapy,re cause for growing concern in safety, efficacynd quality. Because organoleptic drawbacks that lead tovoidancend reduceddherence toRV therapeutic regimesnd decrease in the bioavailability of the drug has been found in many cases [7].

As highlighted by Corrêand coworkers, since the decrease of mortality from HIV/AIDSfter introduction ofntiviral treatment has particular importance for the patients with high life expectancys paediatric patients. However, treatment of HIV-positive children remains challenge in HIV therapy, especially children younger than one year [1].

The last World Healthssemblypproved the resolution “Best medicines for children”nd has recently launched the global campaign „Make medicines child size? [7]. Thus, the increased solubility of darunavir when complexed with β-cyclodextrin would contributes to better treatment regimen fordultsnd children thatreble to swallow small tablets or capsules.

The objective of this research was to determine the solubility of inclusion complex darunavir:β-cyclodextrin,ccording to the criteria established by BCSnd to compare their results with those obtained with the free drug, previously studied by our research group [8].

Experimental

Materials

The materials used were darunavir:β-cyclodextrin complex [2], free darunavir lot SRP07000d (Sequoia Research Products, UK)nd β-cyclodextrin (MW = 1135), kindly supplied by Roquette (France).

Method

For this solubility study the shake-flask method waspplied. shaker incubator MA 420 (MarconiTM), spectrophotometer UV 1800 (ShimadzuTM)nd quartz cuvettes with 1 cm optical path was used.

For the free drug solubility test, the drug was tested by equilibrium solubility measurement by saturation shake-flask method. The solubility was evaluated using physiologically relevant solutioncetate buffer pH 4.5, phosphate buffer pH 3.0, phosphate buffer pH 3.0 with 0.5 % Tweennd purified water. It was used 5 mL of medium were pre-heated to 37 °C ± 0.5 beforedding largemount of darunavir raw material. For darunavir:β-cyclodextrin complexnmount of powder equivalent to 5 mg of darunavir was weighed onnnalytical balance model DV215CD (OhausTM) from pool of darunavir:β-cyclodextrinnd transferred to each test tube containing 300 μL of the same test solutions.

The tubes were sealed with parafilmnd rotatedt 60 rpm in orbital shaking platform incubator.fter 72 hours the samples were filtered through hydrophilic membrane of polytetrafluoroethylene (PTFE) with pore size of 0.45 mnd diameter of 47.0 mmnd some dilutions were carried out. For darunavir free drug, 0.2 mL of the filtered were pipetted into 5 ml volumetric flask, diluted with the same medium. For darunavir:β-cyclodextrin complex 20 μL of filtrate was diluted in varyingmounts of dissolution medium to obtainbsorbance ofbout 0.5nd the spectrophotometric reading performedt 267 nm in the zero order derivative UV spectrum.ll solutions were measuredt 276 nm in the first order derivative UV spectrum,lways using dissolution medias blank. The used spectrophotometric method was previously validated [9]. The solubility in each medium was determined in triplicate.

To calculate the concentration was carried out standard containing free darunavirt the concentration of 15 μg mL-1 for each tested solution. The results were obtained for darunavir free drugnd darunavir:β-cyclodextrin complex were comparednd the role performed by the complex over the darunavir solubility was evaluated.

Results

The figure 3 shows the test tubes containing the darunavir:β-cyclodextrinnd the excesst the bottom of the tubefter 72 hours of test.

pharmacology-toxicological-studies-Tube-darunavir-phosphate

Figure 3: Tube containing (A) darunavir:β-cyclodextrin (B) in phosphate buffer solution 0.05 M with 0.5 % Tween pH 3.0, (C) after 72 hours on shaker at 60 rpm and 37 °C ± 0.5 °C. (D) Detail of the presence of precipitate, ensuring saturation of the solution.

Thebsorbance values of free darunavirt concentration of 15 mg ml-1 in solvents testedre shown in Table 1.

pharmacology-toxicological-studies-Absorbance-free-darunavir

Table 1: Absorbance values of free darunavir in different solvents at a concentration of 15 mg mL-1

Table 2 shows the comparisons of dilutions performed with the different solvents tested to obtain the samebsorbance value.

pharmacology-toxicological-studies-dilution-absorbance-darunavir

Table 2: The needed dilution to obtain approximately the approximately the same absorbance value for each sample of darunavir:β-cyclodextrin complex at the end of the solubility test

To prove that the β- cyclodextrin does notbsorbt wavelengths used, the whole test was done using β- cyclodextrinlone. The valuesre shown in Table 3.

pharmacology-toxicological-studies-absorbance-cyclodextrin-solvents

Table 3: Values of the absorbance of β-cyclodextrin in different solvents

The free darunavir had relatively low solubility, mainly if compared to darunavir:β-cyclodextrin data. The dilutionpplied for the filtered samples of free drug was 0.2 mL of sample to 2 mL of tested solution. The resultsre shown in Table 4.

pharmacology-toxicological-studies-Solubility-darunavir-equilibrium

Table 4: Solubility of free darunavir accessed by equilibrium method

Discussion

The solubility of drug depends on its molecular propertiesnd itsbility to form hydrogen bonds with water molecules.

In the solubility test of darunavir:β-cyclodextrin complex were evaluated four solvents, purified water with pH 8.0,cetate buffer 0.05 M pH 4.5, phosphate buffer 0.2 M pH 6.8nd phosphate butter 0.05 M with 0.5 % Tween pH 3.0. The free darunavir presents pH 5.0nd five values of pKa 1.66, 1.76, 7.75, 11.43nd 14.31. The inclusion complex presents pH 4.5. Weaklycidic drugs, exposed to dissolution medium having pKa greater than the drug pH tend to have increased solubility. Thus, the bioavailability isffected by changes in pH during the dissolution of the drug,nd even by changes in the formulation of pharmaceutical forms [3].

The results showed that the β-cyclodextrin complex contributes to huge increase in drug solubility. The complex has 28 times higher solubility than free darunavir incetate buffer solution 0.05 Mt pH 4.5; 23 times when using the water purified, 22 times when using phosphate buffer solution 0.2 Mt pH 6.8nd 5 times when using phosphate buffer solution 0.05 M with 0.5 % Tweent pH 3.0.

Thismazing improvement in solubility of darunavir can be explained by changes in the crystalline form of the drug. Darunavir:β-cyclodextrin hasmorphous form.morphous form drugs has rapidlyqueous dissolutionndre generally betterbsorbed, since the moleculesre randomlyrranged, requiring less energy to separate each other, resulting in faster dissolution [10]. The darunavir solvated form, the commercial form of the drug [11], has crystalline form with ordered form of molecules which requires more energy to break thempart. May be due toll this, the inclusion complex showed higher solubility inll solvents tested when compared to the free darunavir.

The determination of the solubility of drugs is fundamental part in BCSnd currentlylsossumes great political importance, since this test, together with the permeability, constitutesn essential criterion for bio-exemption in obtaining registration of genericnd similar medicines. The bio-exemption enables the reduction of costnd time of drug development, which benefits the patient by havingccess to cheaper drugs that leads to compliance with pharmacotherapy,nd the public health, by having greater diversity of drugs for the treatment of large number of diseases.

Conclusion

Solubility test inclusion complex darunavir:β-cyclodextrin was performed by the equilibrium methodnd showed higher solubility than the free drug inll dissolution media tested, which makes this recentdvancement of pharmaceutical technologyn important milestone for the use ofntiretroviralnd for the public health.

We must remember that treatment failure not onlyffects the quality of life of patients, butlso contributes significantly to the economic burden of the health system [4]. Therefore, complexation developed is extremely interesting, both from technological point of viewnd financial [2].

Acknowledgments

Theuthorscknowledge CNPq (Brasília, Brazil), FAPESP (São Paulo, Brasil), CAPES (São Paulo, Brasil)nd PADC/FCF/UNESP (Araraquara, Brazil).

References

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