Purpose Bortezomib (Velcade) is an antineoplastic drug widely used in the treatment of multiple myeloma. According to the manufacturer, once reconstituted, bortezomib is only stable for 8 h at 25 °C. The aim of this study was to evaluate the stability of reconstituted bortezomib stored in original vials and syringes at 4 °C and 28 °C, for up to 10 days.
Methods Samples were prepared by dissolving 3·5 mg of bortezomib powder in 3·5 ml of physiological saline (final concentration 1 mg/ml) under routine clinical conditions. Samples were stored in vials or syringes at 4 °C and 28 °C with photoprotection, and drug stability was analysed by high performance liquid chromatography.
Results Bortezomib was stable in both original vials and syringes for up to 10 days at 4 °C with photoprotection. Furthermore, it was stable for up to 8 days at 28 °C in original vials with photoprotection.
Conclusions Our results showed an extended stability of bortezomib prepared under routine clinical conditions and stored at 4 °C, which could make an important contribution towards reducing drug waste and, consequently, improving cost efficiency.
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Bortezomib, known under the commercial name of Velcade, is an antineoplastic agent which reversibly inhibits the activity of the 26S proteasome. Bortezomib has been approved for use in monotherapy to treat progressive multiple myeloma in patients who have received at least one previous therapy and who have already undergone or are unsuitable for bone marrow transplantation, and in combination with melphalan and prednisone for patients with previously untreated multiple myeloma who are not eligible for high dose chemotherapy with bone marrow transplantation. Recent studies have also suggested a possible role for this drug in the prevention of graft rejection in renal transplantation.1 According to information supplied by the manufacturer, once reconstituted, bortezomib may be stored in vials or syringes at 25 °C but should be administered within 8 h.2 This leads to significant waste of residual drugs and higher costs, considering that patients generally receive twice weekly administrations on days 1, 4, 8 and 11. Despite the best efforts of compounding centres to centralise preparation and administration of therapies on the same day, the short stability of bortezomib remains a major limitation. A few studies recent studies have tried to establish the stability of bortezomib in original vials, but with different results, all suggesting the possibility of preserving residual drugs which could be used later.3–5 Some data are also available on the extended stability of bortezomib reconstituted in syringes and refrigerated for up to 5 days.6
The published literature has demonstrated a different stability of bortezomib compared with that indicated by the manufacturer. Therefore, our study aimed to evaluate the stability of bortezomib prepared according to our routine clinical operating conditions (using standardised procedures, facilities and medical devices) both in vials and syringes and stored at 4 °C and 28 °C for up to 10 days. To ensure clinical validity, samples were prepared in different compounding centres and sent to a single laboratory for stability analysis. Given the growing number of indications for use, an extended stability would facilitate better organisation of compounding centres, while at the same time reduce costs.
High performance liquid chromatography analysis
We used the modified method of André et al6 to separate bortezomib by its degradation products and to quantify bortezomib, to assess its stability. The high performance liquid chromatography (HPLC) system was equipped with an ultraviolet light detector set at 270 nm, an injector device to deliver 20µl, a recording integrator and a C18 inverse phase column (Betasil column Thermo scientific, 250 mm × 4 mm, particle size 5µm). The mobile phase consisted of a mixture of methanol (Chromasolv Methanol; Sigma-Aldrich, Steinheim, Germany) and phosphate buffer 40 mM (potassium phosphate monobasic; Sigma-Aldrich) at pH 7·00 (50/50 v/v), pumped at a flow rate of 1·4 ml/min. A run time of 30 min was used and the retention time for bortezomib was about 21 min. A standard calibration curve was prepared by injecting known concentrations of bortezomib into the HPLC column (2·5, 5·0, 7·5, 10·0 and 12·5µg/ml). Bortezomib was reconstituted each day. Method precision was evaluated by injecting six test solutions of bortezomib 7·5µg/ml to simulate the concentration used in the stability study.
To ensure uniformity of results, samples were prepared and transported according to an established protocol by the Oncology Network of Hospital Pharmacies of Emilia Romagna. To avoid potential microbial or particulate contamination, all solutions were prepared under aseptic conditions in a laminar flow hood. Test syringes (3 ml BD Plastick Luer-Lock polypropylene syringes) were prepared at two different sites (Oncology Pharmacy Services of Ravenna and Istituto Scientifico Romagnolo per lo Studio e la Cura dei Tumori, Meldola) while test vials were prepared at Biochem Sas Laboratory (Bologna, Italy). Bortezomib powder 3·5 mg (Velcade powder glass vials for injection solution, Janssen-Cilag International NV, Beerse, Belgium; lot 9GZSK01, expiration date June 2012) was reconstituted in 3·5 ml of physiological saline (physiological saline, Fresenius Kabi Italia, Isola Della Scala, Verona, Italy; lot 19CE05GB, expiration date 5 April 2012; final concentration: 1 mg/ml) in the original vial and then 1·75 ml of this solution was transferred to a polypropylene syringe. Samples at time 0 were collected and transported to the Biochem Sas Laboratory within 2 h after preparation. To avoid the possibility of degradation during transfer, samples were transported in temperature controlled boxes with data loggers. HPLC analysis was performed within 2 h after sample delivery. A 75µl aliquot of each sample was diluted in 10 ml of the mobile phase medium and 20µl of this solution was injected into the HPLC column for analysis.
Storage conditions were as follows: two vials were stored in a thermostat at 28 ± 2 °C for 10 days with photoprotection; two vials were stored at 4 ± 2 °C for 10 days with photoprotection; two syringes were stored in a thermostat at 28 ± 2 °C for 10 days, with photoprotection for 22 h a day and then exposed to indirect sunlight for 2 h a day; and two syringes were stored at 4 ± 2 °C for 10 days with photoprotection. Photoprotection was provided by covering the samples with aluminium foil. Each sample was analysed in duplicate at times 0, 5, 8 and 10 days.
An accelerated degradation study was performed to establish the stability indicating nature of the assay and to test the ability of the chromatographic method to separate bortezomib from its degradation products. As an accelerated test is designed to increase the rate of chemical degradation or physical change of a drug substance or drug product by using exaggerated storage conditions,7 a known quantity of drug (concentration 1 mg/ml) was dissolved in a 1 M potassium hydroxide solution and stored in vials at 60 °C. Samples were removed at times 0, 15, 25 and 35 min and neutralised in phosphate buffer at pH 7·00 to avoid damage to the HPLC equipment.
The mean concentration of bortezomib at time 0 was designated 100 % and all subsequent samples were expressed as a percentage of this starting concentration. According to the US Food and Drug Administration, a ‘significant change’ for a drug product is defined as a 5 % change in assay from its initial value7 and/or as failure to meet the acceptance criteria for appearance, physical attributes (eg, colour). Therefore, we agreed on clear and colourless samples with a concentration of at least 95 % as the limits of stability.
Accelerated degradation study and assay validation
Complete degradation of bortezomib was observed at 60 °C. Although many degradation products were formed, they did not elute with bortezomib. Figure 1A shows the characteristic peak of bortezomib at storage time 0, with a retention time of 21 min. After 15 min at 60 °C, some weak degradation product peaks started to appear after a few minutes but the characteristic bortezomib peak was still high (data not shown). After 25 min, the characteristic bortezomib peak decreased while new peaks at a retention time of 2 min appeared (figure 1B).
The HPLC method was shown to be stability indicating as it was able to separate all of the degradation products of bortezomib.
The method was linear over the range 2·5–12·5µg/ml, with a correlation coefficient of R2 = 0·9992. The intraday precision, expressed as relative SD, was less than 1 % (n = 6 injections, concentration 75µg/ml). The interday coefficient of variation (n = 6 injections, concentration 75µg/ml for 3 consecutive days) was less than 2 %.
Stability of bortezomib
Based on the stability limit of >95 % drug product remaining from its initial value, bortezomib was stable at 28 °C for up to 8 days in vials, while the mean concentration decreased to 69·10 % on day 10. As shown by the chromatogram in figure 2, first degradation products started to appear at a retention time of 2 min. Within method precision, no degradation products were observed on analysis at time t = 0, 5 and 8 days (chromatograms not shown). In contrast, at the same storage temperature, bortezomib was only stable in syringes at time 0, with mean concentrations falling below 95 % on days 5, 8 and 10 (table 1). As shown by the chromatogram in figure 3, the first degradation products started to appear at a retention time of 2 min. These degradation products were observed on sample analysis at time t = 5, 8 and 10 days (chromatograms not shown). Meanwhile, bortezomib was stable at 4 °C for up to 10 days in both vials and syringes (table 2). All solutions remained clear and colourless.
The safe preparation of cytotoxic drugs is assured by centralised units in the hospital pharmacy. Each preparation has to keep its physical and chemical properties from the beginning of preparation until the end of administration to the patient. In general, manufacturers provide minimal information relating to stability data; therefore, it is the pharmacist who is responsible for the retrieval and interpretation of existing data on stability, or to perform such studies.8
There are several reasons for studying the stability of cytotoxic drugs: to enhance the stability of very short stability data, to allow preparation for the weekend or for the treatment cycle, and to save money minimising residual waste.8
Product information states that reconstituted bortezomib, commercialised under the tradename of Velcade, is stable for up to 8 h when reconstituted and stored in original vials or syringes at <25 °C and protected from light. This limited stability generates a large quantity of daily residual drugs and, consequently, leads to increased expenditure. Therefore, proof of an extended stability of bortezomib could have a significant impact on these aspects, if we consider that in the region of Emilia Romagna alone a residual drug waste of 550 000 Euros was estimated for the treatment of 338 patients in 2010. This large amount of money represents 12·5 % of the total regional expenditure for chemotherapy drugs and would be greatly reduced by the extension of drug stability.
The aim of this study was to examine the stability of bortezomib reconstituted and stored in vials and syringes at 4 °C or 28 °C for 10 days with photoprotection. The HPLC assay was found to be suitable for checking the stability of bortezomib.
Our results demonstrated that bortezomib is stable at 28 °C for up to 8 days, but only when stored in the original vials with photoprotection. Furthermore, bortezomib is stable at 4 °C for 10 days when protected from light both in vials and in syringes.
Considering the high cost of this drug and the preparation of syringes in the centralised units, our results may allow better use of bortezomib, offering significant savings in costs and pharmacy resources.
The authors would like to thank Biochem SaS and Dr Giulia Arniani for their collaboration in completing this research, and Dr Ian Seymour for editing the manuscript.
Funding This study was financially supported by regional funds as a part of a project studying the stability of oncology drugs set up by the Oncology Network of Hospital Pharmacies of Emilia Romagna.
Competing interests None.
Provenance and peer review Not commissioned; externally peer reviewed.
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