STABILITY OF CEFUROXIME AXETIL ORAL SUSPENSION AT DIFFERENT TEMPERATURE STORAGE CONDITIONS

Stability testing of an active substance or fi nished product provides information of the variation of drug substance or fi nal product with time infl uenced by a variety of environmental factors such as temperature, humidity and light. Knowledge gained from stability studies enables understanding of the eff ects of the environment on the drugs. Th e aim of our study was to determine the stability of cefuroxime axetil oral suspension at diff erent temperature storage conditions (stored at room /oC/ and refrigerated /oC/ conditions). Determination of cefuroxime (as cefuroxime axetil) was performed by dissolution testing. Fractions of the released cefuroxime axetil were compared using f value. After interpolating data for dissolution profi les at room and refrigerated conditions the following fvalues were obtained: ,; , and , on rd, th and th day, respectively. Th ese values indicate similarities in drug release from analyzed cefuroxime axetil oral suspension on rd, th day, and diff erences on th day. Based on our results, we may assume that cefuroxime axetil oral suspension preserves its stability for  days after reconstitution under room and refrigerated conditions. It is obvious, according to the f value obtained on the th day, that there is a diff erence between the released ceforoxime axetil from oral suspension at room (,) and refrigerated (,) conditions. Concentration changes can be caused by the mechanisms associated with drug release and hydrolytical decomposition of the sample and higher temperatures during longer period of storage.


Introduction
Cefuroxime axetil (-acetoxyethyl ester of cefuroxime) is orally active prodrug of cefuroxime, second generation semi-synthetic cephalosporine antibiotic.Upon oral administration, cefuroxime axetil is absorbed from gastrointestinal tract and rapidly hydrolyzed by nonspecific esterase in the intestinal mucosa and blood releasing microbiologically active form (free acid), cefuroxime.Cefuroxime exerts its bactericidal eff ect against a range of gram-positive and gram-negative bacteria by inhibiting the synthesis of bacterial cell wall (,,).Cefuroxime axetil (Figure .) has a carbamoyl group in position , which accounts for considerable metabolic stability, and a methoxyimino group in position , which provides resistance to β-lactamase attack and, together with a furyl ring, contributes to the antibacterial properties of the molecule by enhancing its activity against Gram-negative bacteria.A -acetoxyethyl ester group in the position  of cefuroxime axetil ensures its lipophilicity and promotes the intestinal absorption of cefuroxime.For the preparation of pharmaceutical formulations only the amorphous form is used.It has better physicochemical and biological properties than the crystalline form, e.g.signifi cantly higher solubility and bulk density as well as higher degree of absorption after oral administration (,).Due to their possible composition, pharmaceuticals are especially sensitive to environmental factors.Strict storage conditions are necessary for the maintenance of integrity and product activity.Stability is defined as the capacity of a drug substance or drug product to remain within the established specifications to maintain its identity, strength, quality, and purity throughout the retest or until expiry date period ().Stability testing of an active substance or finished product provides information on how the quality of drug substance or drug product varies with time influenced by a variety of environmental factors such as temperature, humidity and light.Knowledge from stability studies enables understanding of the long-term effects of the environment on drugs ().Stability testing also provides information about the degradation mechanisms, potential degradation products, possible degradation pathways of drug as well as interaction between the drug and the excipients in drug product.Th e gained information is applied in the development of manufacturing processes, selection of proper packaging and storage conditions, and determination of product's shelf life and expiration date ().Th e aim of present study was to determine the stability of cefuroxime axetil oral suspension at diff erent tem-perature storage conditions (stored at room / o C/ and refrigerated / o C/ conditions).Determination of cefuroxime (as cefuroxime axetil) was performed by dissolution testing.

Material and Methods
Reagents Th e reagents used were of analytical grade, unless otherwise stated.Cefuroxime axetil working standard was provided by GlaxoSmithKline.Sodium dihydrogen phosphate and disodium hydrogen phosphate were provided by Carl Roth GmbH & Co. (Karlsruhe, Germany).

Preparation of standard solutions
A standard curve of absorbance versus concentration was constructed using dilutions of cefuroxime axetil in the dissolution medium (phosphate buff er, pH=,; previously degassed) ranging in concentration from , to , mg/ml.Absorbance versus concentration plot was linear over this concentration range and was used to determine percent of drug dissolved in the dissolution experiments.UV absorbance of each standard solution was measured spectrophotometrically at  nm.

Dissolution test conditions and analysis procedure
Th e dissolution tests of cefuroxime axetil oral suspension (n=) were performed using USP apparatus  , Van Kel VK  dissolution tester, at a stirring speed of  rpm (Van Kel, Cary, NC, USA).Th e dissolution apparatus was maintained at °C throughout the experiment.Cefuroxime axetil oral suspension, when reconstituted in water, provides the equivalent of  mg of cefuroxime per  ml of suspension.Reconstituted oral suspension in the amount of  ml was transferred into test tube and slowly added to dissolution medium.Samples in the amount of  ml were withdrawn at the following intervals:  th ,  th ,  th and  th min.Prior to use, the dissolution medium was equilibrated at   C overnight to deaerate the medium.Th e dissolution tests of cefuroxime axetil oral suspension (n=) at diff erent temperature storage conditions (stored at room / o C/ and refrigerated / o C/ conditions) was performed on  rd ,  th and  th day.Dissolution samples were collected for the analysis.Correction for volume was calculated mathematically, considering that withdrawn samples were not supplemented with an equal volume of fresh dissolution fl uid to maintain a constant total volume.Th e samples were filtered using a , Pm membrane filter (Sartorious GmbH, Goettingen, Germany).Th e dissolution apparatus was connected with UV/VIS spectrophotometer Shimadzu  (Shimadzu, Kyoto, Japan).Determination of dissolution rates for the active ingredient in oral suspension is carried out according to the previously mentioned spectrophotometric method.All dissolution tests were performed in triplicate.Model independent approach that compare the dissolution profi les was applied to the dissolution data in this study.Th e data were analyzed using pharmacopeial test for similarity of dissolution profi les (f equation), previously proposed by Moore and Flanner ().

Results and Discussion
The results of our studies are summarized in Tables -, and Figures -, which show the fraction of the dissolved drug as a function of time.In vitro release of cefuroxime axetil from oral suspension fulfi lled offi cial requirements if the dissolution of each of the six samples was not less than  of the declared contents in  minutes.Our tests were carried out for a period of  minutes.In our study, in vitro release of cefuroxime axetil fulfi lled these requirements and exhibited release profile: , and ,, for  and  minutes, respectively.Concentration changes of cefuroxime axetil under the experimental (room and refrigerated) conditions were assessed by means of dissolution testing and spectrophotometry, too.Fractions of cefuroxime axetil released in dissolution medium were calculated from calibration curves.Th e data were analyzed using pharmacopeial test for similarity of dissolution profi les (f equation).Th e f value between  and  suggests that the dissolution profi les are similar.Th e value of  suggests that the test and reference dissolution profi les are identical.Fractions of the released cefuroxime axetil were compared using this value.After interpolating data for dissolution profi les at room and refrigerated conditions the following f values were obtained: ,, , and , on  rd ,  th and  th day, respectively.Th ese values indicate similarities in drug release from analyzed cefuroxime axetil oral suspension on rd, th day, and diff erences on  th day.

TABLE 2 .
Fraction of dissolved cefuroxime axetil from oral suspension as a function of time (3 rd day).

TABLE 3 .
Fraction of dissolved cefuroxime axetil from oral suspension as a function of time (6 th day).In vitro release of cefuroxime axetil from oral suspension fulfi lled offi cial requirements ¡ After interpolating data for dissolution profi les at room and refrigerated conditions the following f values were obtained: ,, , and , on  rd ,  th and  th day, respectively.Th ese values indicate similarities in drug release from analyzed cefuroxime axetil oral suspension on  rd ,  th day, and diff erences on  th day.¡ On the basis of the results in this study, we can assume that cefuroxime axetil oral suspension preserves its stability during  days after reconstitution under room and refrigerated conditions.It is obvious, according to the obtained f value on the th day, that there is diff erence between released ceforoxime axetil from oral suspension at room (,) and refrigerated (,) conditions.¡ Changes in concentration may be caused by the mechanisms associated with drug release and hydrolytical decomposition of the sample and higher temperatures during longer period of storage.() Carstensen J.T., Rhodes C.T. Drug Stability, Principles and Practices, Marcel Decer, Inc., New York, .() Moore J.W., Flanner H.H. Mathematical comparison of dissolution profi les.Pharm.Tech.;: -.

TABLE 4 .
Fraction of dissolved cefuroxime axetil from oral suspension as a function of time (10 th day).