University of Khartoum

Chemical And Photochemical Stability Of Danazol And Diloxanide Furoate

Chemical And Photochemical Stability Of Danazol And Diloxanide Furoate

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Title: Chemical And Photochemical Stability Of Danazol And Diloxanide Furoate
Author: Ahmed, Elrasheed
Abstract: The stability studies carried here for danazol (DZ) and diloxanide furoate (DF), were initiated as a part of preformulation studies to characterize the physicochemical properties of these selected drugs and to aid in the development of possible formulations of these drugs other than their available solid dosage forms. Two selective high-performance liquid chromatographic (HPLC) procedures were developed for the stability-indicating determination and kinetic studies of DZ and DF in the presence of their chemical or photochemical degradation products. The parameters that reflect system suitability for the developed HPLC methods i.e. column/mobile phase efficiency were investigated. These included relative capacity factor or selectivity, resolution, tailing factor, number of theoretical plates (N) and height-equivalent to theoretical plate (HETP). Results were compared with reference standard data implemented for good system suitability in official pharmacopoeias or other relevant references. The stability-indicating power of the developed methods was validated by UVdegraded and chemically-degraded solutions of DZ and DF. The accuracy and reliability of the proposed HPLC methods were also validated by the linearity data of standard solutions of both drugs [correlation coefficient values, r, >0.995]. Assay percent and added recoveryresults were within RSD values of <2% for replicate results. The stability-indicating superiority of the developed vii HPLC method over UV-spectrophotometry was also ascertained. Interference with the assay of both drugs by the UV procedure, in presence of their degradation products, was significant. The application of t-test and F-test confirmed the accuracy and precision of the developed HPLC methods as compared to the official methods. The structures of both drugs incorporate functional groups liable to chemical and photochemical reactions. The photochemical experiments conducted on both drugs in glass bottles or quartz cells revealed the photosensitivity of both drugs. The drugs were subjected to different light exposures i.e. UV-irradiation [at 254nm (UV-C range) and 366nm (UV-A range)], roomartificial light and sunlight. The effects of different solvents on the photodegradation of both drugs were also investigated. DZ was found more photolabile than DF. DZ undergoes photodegradation over the whole range of UV-visible range with fast photolysis in quartz cells (t½value ≈2 minutes) and in glass bottles, (t½ value ≈20 minutes). The drug is more stable in methanol and less stable in solutions containing water. This is in contrary to DFwhich is more stable in aqueous media than in solutions containing alcohols due to the involvement of a transesterificatoin reaction. The t½values for solutions of DF irradiated in quartz cells is about 2-8 minutes depending on the amount of water in the solution; in glass bottles, t½values of more than 2 days were obtained for DF. DZ also undergoes fast photolysis in sunlight; the t½value was less than 2 viii days, compared to that of about 10 days calculated for DF under the same conditions. Irradiation of DZ at 366 nm, gave a t½value of about 27 minutes ± 2; while DF showed slightphotodegradation within 24hours exposure. The use of UV-absorbers (ascorbic acid and para-aminobenzoic acid (PABA) and a commercially available Tang®preparation (containing mainly ascorbic acid, a colouring material in a buffered system) enhanced the photostability of both drugs irradiated at 254 nm or 366. Ascorbic acid showed less photostabilizing effect on DZ. The mechanism of photostability is suggested to involve spectraloverlay effect. The degradation kinetics of methanolic solution of danazol (0.002%) in aqueous buffers and sodium hydroxide was investigated using the stabilityindicating HPLC method. The drug degrades in alkaline medium through a base-catalysed proton abstraction rather than via an oxidative mechanism involving oxygen species. The degradation followed pseudo-first-order kinetics and the pH-rate-profile implicated specific base catalysis. The stability of the drug was found to be dependent on pH, buffer concentration, buffer species (acetate, borate, phosphate) and temperature. The ionic strength did not affect the stability of the drug. According to Arrhenius plot, the activation energy was estimated to be 22.62 kcal mol −1 at pH 12 and temperatures between 30-60°C. Two major hydrolytic degradation products, namely cyanohydrin and a hydroxyacid derivatives, were separated and identified by IR, NMR and mass spectrometry and a degradative pathway suggested. ix The degradation of the amoebicide diloxanide furoate in alkaline medium at different temperatures was investigated using both a spectrophotometric and the developed HPLC method. In solutions, the drug was found to undergo decomposition that is temperature- and pH-dependent. The pH-rate profile at pHs between 7.6-9.6 indicated a first-order dependence of Kobson [ − OH]. Arrhenius plot obtained at pH8 was linear between 40-63°C. The estimated activation energy of hydrolysis was 18.25 kcal mol −1 . A new thin-layer chromatographic (TLC) procedure for the fractionation of the drug and its alkaline hydrolysis products was developed and found to compare favorably with that of the British Pharmacopoeia (B.P.). Three hydrolytic products of a basic methanolic solution of the drug, namely furoic acid, diloxanide and methylfuroate, were identified by the use of TLC, HPLC, infra-red, and mass spectrometry. The chemical stability of DZ in aqueoussolutions containing sucrose, glucose, fructose, lactose, sorbitol and cyclodextrins (β-cyclodextrin and hydroxypropyl-β-cyclodextrin) was investigated for 30 days in acid media at room temperature (25°C±1) in the dark. DZ was stablein all these media (pH range 3−6.5). The drug was also stable in a commercially available Tang ® preparation containing sugar, buffers, stabilizers and artificial colours (pH 3.0 in solution). In alkaline media (pHs 10.4 and 11.0) at 65°C, sucrose, sorbitol and the cyclodextrins accelerated the rate of hydrolysis of DZ in the order of x 4−7. The accelerated rate ofhydrolysis of DZ in the presence of sucrose, sorbitol and the cyclodextrins in alkaline medium is proposed to be due to an enhanced proton abstraction followed ring opening. The effects of aqueous solutions containing sucrose, glucose, fructose, lactose and sorbitol on the chemical stabilityof diloxanide furoate (DF) was investigated in acid and alkaline media at room temperature (25°C±1) and at 40°C. All the compounds accelerated the rate of hydrolysis of DF in alkaline medium at 40°C. At room temperature, different brands of sucrose and glucose had adverse effects on the stability of DF. DF was relatively stable in fructose, lactose and sorbitol as well as inthe commercially available Tang ® preparation. The optimum pH range of stability ofDF in solutions containing these carbohydrates lies around pH < 4.5. The effect of β-cyclodextrin (β-CD) and hydroxypropyl-β-cyclodextrin (HP-β-CD) on the chemical stability of DF at pH values of about 9 in borate, phosphate, and tris buffer had an adverse effect on the stability of DF showing a relative enhancement inthe hydrolysis rate in the order of about 1.7-2.0. The observed accelerated rate ofhydrolysis of DF by carbohydrates in alkaline medium is proposed to involve a nucleophilic reaction mechanism. The effect of simulated gastric and intestinal fluids on DZ stability was investigated. No effect was observed on danazol solutions incubated in the gastric or intestinal fluids, indicating that the drug passes these media without xi being subjected to chemical or enzymatic reactions. However, the in vitro metabolism of danazol using liver homogenate led to the formation of the two metabolites quoted in the literature; one metabolite was confirmed by HPLC and TLC as ethisterone by comparison withreference ethisterone retention time and Rf values; the other metabolite, believed to be 2-hydroxymethyl ethisterone was not confirmed due to lack of authentic material. The effect of simulated gastric and intestinal fluids on the hydrolysis of DF was also investigated. The results of the stability study on DF in simulated gastric and intestinal fluids confirmed its hydrolysis, in the intestine, to its active form diloxanide and to furoic acid. It is alsoestablished that the hydrolytic reaction is an enzyme-catalysed process that takes place in the intestine. Chymotrypsin seems to be the major enzyme involved in DF metabolism in the intestine. In conclusion the stability results obtainedin this study for DZ and DF revealed their stability in acid media and lability to alkaline media. Optimal pH for the stability of both drugs in presence ofcarbohydrates or polyols, or the Tang ® preparation was 3-4. The photolability of both drugs necessitates special storage conditions and protection from light. The Tang ® preparation used in these studies proved its efficiency as a chemical and photochemical stabilizer of both drugs due to its components and buffered pH of 3. Accordingly we recommended the use of the Tang ® preparation as an effective diluent which can act as flavouring, colouring, stabilizing and sweetening agent
URI: http://hdl.handle.net/123456789/8213
Date: 2015-04-03


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