Abstract
Introduction
The aim of this study was to determine and compare the physicochemical stability of two carmustine-containing medicinal products licensed and marketed in Europe as Carmustin Obvius (Medac GmbH) and Carmubris (Tillomed Pharma GmbH). Reconstituted stock solutions and diluted ready-to-administer infusion solutions of the two products were investigated.
Methods
Reconstituted carmustine stock solutions (3.3 mg/mL) and ready-to-administer infusion solutions (0.2 mg/mL, 1.0 mg/mL) prepared in prefilled 5% glucose injection solution PP/PE bags were stored at 22°C or 2–8°C over a maximum period of 66 hours protected from light. Samples were taken immediately after reconstitution or dilution and after 3.5, 6, 8.5 and 11 hours when stored at 22°C or after (12), 24, 48 and 60 hours when stored at 2–8°C, followed by 3- and 6-hour storage at 22°C (60+3 hours, 60+6 hours). Physicochemical stability was determined by reversed-phase high-performance liquid chromatography with UV detection, measurement of pH, osmolarity and inspection for visible particles or colour changes.
Results
Carmustin Obvius and Carmubris reconstituted stock solutions were physicochemically stable for at least 48 hours when stored at 2–8°C. Carmustin Obvius and Carmubris infusion solutions 0.2 mg/mL were physicochemically stable for at least 8.5 hours and 60 hours when stored at 22°C and 2–8°C, respectively. After subsequent storage of the 60-hour refrigerated test solutions for 3 hours at 22°C, the carmustine concentrations averaged the 90% limit and fell below the 90% limit after 6 hours. Carmustin Obvius infusion solutions 1.0 mg/mL were physicochemically stable for at least 8.5 hours when stored at 22°C and for 60 hours when stored at 2–8°C.
Conclusion
According to the physicochemical stability data, the shelf life (95% limit) of the refrigerated stock solutions is 48 hours and the shelf life (90% limit) of ready-to-administer infusion solutions (0.2 mg/mL, 1.0 mg/mL) is 60 hours at 2–8°C or 8.5 hours at 22°C under light protection. These results facilitate the use of both medicinal products in a pharmacy-based centralised cytotoxic preparation unit.
Keywords: clinical medicine, analytic sample preparation methods, chemistry, pharmaceutical, medical oncology, pharmaceutical preparations
Introduction
The antineoplastic activity of carmustine (N, N′-bis (2-chlorethyl)-1-nitrosourea, abbreviated BCNU, MW 214.05 g/mol) is based on the alkylation of the DNA/RNA nucleoproteins and less significantly on the carbamylation of lysine residues in enzymes causing irreversible inactivation. Recently, the indication for carmustine was extended to conditioning chemotherapy prior to autologous or allogeneic haematopoietic stem cell transplantation in haematological diseases. The recommended carmustine doses for adults are 150–200 mg/m2 or 300–600 mg/m² in conditioning treatment protocols.1
Carmustine was developed as a medicinal product by Bristol-Myers Squibb and was licensed internationally 40 years ago (trademarks: Carmubris, BCNU). Since 2013 the licences have been held by Emcure Pharmaceuticals, India. The European Medicines Agency authorised Carmustine Obvius as a generic medicine in 2018. Currently, in Germany, the generic and the reference medicines are marketed by Medac GmbH, Wedel, Germany and Tillomed Pharma GmbH, Schönefeld, Germany, respectively. The products are available as powder (100 mg) and solvent (3 mL ethanol) for concentrate for solution for infusion. The pharmaceutical details of the two products are shown in table 1.
Table 1.
Pharmaceutical details of Carmustin Obvius (Medac GmbH) and Carmubris (Tillomed Pharma GmbH) according to the Summary of Product Characteristics1 2
| Product | Carmustin Obvius (Medac GmbH, Wedel, Germany) | Carmubris (Tillomed Pharma GmbH, Ahrensberg, Germany) |
| Active substance | Carmustine | Carmustine |
| Medicinal product | Carmustin 100 mg powder and solvent for concentrate for solution for infusion | Carmubris powder and solvent for preparing an infusion solution |
| Excipients | No | No |
| Powder | White to almost white powder or lyophilisate | Powder, lyophilisate |
| Refrigerated storage and transport | Refrigerated storage | |
| Maximum temperature 30°C | Maximum temperature 27°C | |
| Solvents | 3.0 mL ethanol anhydrous 27.0 mL water for injection |
3.0 mL ethanol absolute 27.0 mL water for injection |
| Stock solution | 3.3 mg/mL carmustine | 3.3 mg/mL carmustine |
| Clear, colourless to light yellow | Clear, colourless to light yellow | |
| pH 4.0–5.0 (EPAR)9 | pH 5.6–6.0 | |
| Diluent in glass containers | 500 mL 5% glucose solution for injection 500 mL 0.9% sodium chloride solution for injection |
500 mL 5% glucose solution for injection 500 mL 0.9% sodium chloride solution for injection |
| Concentration in diluted infusion solutions | 0.2 mg/mL carmustine (0.5 mg/mL, 1.0 mg/mL in conditioning treatment) |
0.2 mg/mL carmustine |
| pH and osmolarity of diluted (ready-to-administer) infusion solutions | pH 4.0–5.0 and 385–397 mOsm/L if stock solution is diluted in 5% glucose solution for injection; pH 4.0–6.8 and 370–378 mOsm/L if stock solution is diluted in 0.9% sodium chloride solution for injection | NA |
| Shelf life after reconstitution | Not declared | 24 hours at 2–8°C |
| Shelf life of the ready-to-administer infusion solution | 3 hours | 8 hours at room temperature protected from light 24 hours at 2–8°C and further 6 hours at room temperature protected from light |
EPAR, European Public Assessment Report; NA, not available.
Prior to infusion, the stock solutions are to be diluted with 5% glucose or 0.9% sodium chloride injection solution.1 2 Carmustin Obvius infusion solutions should be administered immediately after reconstitution by intravenous drip under light protection via a polyvinylchloride-free polyethylene (PE) infusion set over a 1–2 hour period.
Carmustine is unstable in aqueous solutions and degrades spontaneously to reactive intermediates that are also capable of alkylation and carbamylation. It is known from the literature that the degradation of reconstituted and diluted infusion solutions depends mainly on pH, but also on temperature and light.3 4 Of the known high-performance liquid chromatography (HPLC) methods used for the analysis of carmustine,4–7 the current method specifically developed for the medicinal product has been adopted and modified.8
In the official documents of the licensed products, different information is given about the in-use shelf life at room temperature of the reference (8 hours) and the generic product (3 hours; see table 1). However, the assessment report of Carmustin Obvius states that the reconstituted/diluted generic and ‘reference product Carmubris shows similar degradation tendencies’9 at room temperature with a decrease of approximately 4–5% and 6–7% in content after 3 hours and 4 hours, respectively.9 Data regarding the physicochemical stability of reconstituted and diluted Carmustin Obvius stored under refrigeration are not available, but these are crucial for shelf life determination in pharmacy-based centralised cytotoxic preparation units.
The aim of this study was to determine and compare the physicochemical stability of Carmustin Obvius and Carmubris reconstituted stock solutions and diluted infusion solutions, concentration 0.2 mg/mL and 1.0 mg/mL, in polypropylene/polyethylene (PP/PE) bags prefilled with 5% glucose (G5) vehicle solution. Physicochemical stability of the test solutions was analysed by reversed-phase high-performance liquid chromatography (RP-HPLC) with UV detection, measurement of pH and osmolarity, and by observation of visible particles and colour changes.
Materials and methods
Preparation of test solutions
The stability tests were performed with the authorised and marketed medicinal products. Test solutions were stored protected from light, either refrigerated at 2–8°C or in a climatic chamber (ICH260L, Memmert) at 22°C. For each medicinal product, storage condition and concentration, three test solutions were prepared.
Stock solutions
Carmustin Obvius (Medac GmbH; Carmustin: batch 1805502, expiry date August 2020, ethanol: batch 80 528A, expiry date May 2020) and Carmubris (Tillomed Pharma GmbH; Carmustin: batch CDAA919, expiry date June 2021, ethanol: batch DHAA8008, expiry date June 2021) were dissolved with 3 mL of the ethanol attached and further diluted with 27 mL of water for injection (B Braun, Melsungen, Germany; batch 184228091, 194438091). Stock solutions of the nominal concentration 3.3 mg/mL carmustine were stored at 2–8°C.
Infusion solutions
Carmustine infusion solutions (0.2 mg/mL, 1.0 mg/mL) were prepared by injecting 6 mL or 30 mL (20 mg or 100 mg) of freshly reconstituted stock solutions into prefilled G5 freeflex infusion bags of the nominal volume 100 mL (freeflex, Fresenius Kabi, Bad Homburg, Germany; batch 13NGS133, 13MFS302). Due to the 6.0 mL average overfilling of the freeflex bags and the added volume (6 mL, 30 mL) of carmustine stock solution, 12 mL or 36 mL of G5 solution were withdrawn to obtain a final volume of 100 mL in the test infusion bags. Three infusion solutions each were stored at 2–8°C or 22°C.
Preparation of samples
Stock solutions
Immediately after reconstitution and after 12, 24 and 48 hours storage at 2–8°C, 1.0 mL samples were withdrawn from each stock solution and further diluted in HPLC vials to fit the calibration curve by mixing 60 µL aliquots with 940 µL G5 (B Braun, Melsungen, Germany; batch 19351015, 19222010) to a final concentration of 0.2 mg/mL in triplicate.
Infusion solutions 0.2 mg/mL
Immediately after dilution and after 12, 24, 48 and 60 hours storage at 2–8°C, and after an additional 3 and 6 hours storage at 22°C or after 3.5, 6, 8.5 and 11 hours storage at 22°C, 1.0 mL samples were withdrawn in triplicate and assayed without further dilution.
Infusion solutions 1.0 mg/mL
Immediately after dilution and after 24, 48 and 60 hours storage at 2–8°C, or after 3.5, 6, 8.5 and 11 hours storage at 22°C, 0.2 mL samples were withdrawn and diluted in HPLC vials with 0.8 mL G5 (batch 19351015, 19222010) to a final concentration of 0.2 mg/mL in triplicate.
pH and osmolarity
Undiluted samples were used for measurement of pH and osmolarity at each sampling time point.
HPLC assay
Carmustine concentrations were determined by a stability-indicating RP-HPLC method (see table 2), adopted from a known RP-HPLC assay and slightly modified.8
Table 2.
Characteristics of the RP-HPLC assay based on the method of Allamneni et al 8
| Parameter | Condition/set value |
| Column | C18 ODS HypersilTM, 5 µm, 150 mm x 4.6 mm, Thermoscientific |
| Column temperature | 25°C |
| Sample temperature | 2–8°C |
| Flow rate | 1.5 mL/min |
| Injection volume | 10 µL |
| Run time | 15 min |
| Detection wavelength | 230 nm |
| Mobile phase | 70% water HPLC grade and 30% acetonitrile HPLC grade |
| Flush solution | 95% water HPLC grade and 5% acetonitrile HPLC grade |
| Pump mode | Isocratic |
RP-HPLC, reversed-phase high-performance liquid chromatography.
The HPLC equipment consisted of a Waters Alliance 2695 pump connected to a Waters photodiode array detector 2990 (Waters, Eschborn, Germany). Waters Empower Pro, Empower 2 Software, Version 6.10.01.00 was used for instrument operation, data collection and processing. Samples were injected in triplicate by an autosampler. The retention time of carmustine was about 7–8 min. Test solutions were considered to be stable when the measured carmustine concentration was ≥90% of the concentration measured initially (100%).
Validation of the RP-HPLC assay
The validation was carried out in accordance with the ICH Harmonised Tripartite Guidelines for Validation of Analytical Procedures: Text and Methodology Q2 (R1).10 Linearity testing was performed with a stock solution of 10.0 mg carmustine CRS substance (EDQM Code: Y0002128, Id: 00FvGj, batch 1.0) dissolved in 0.3 mL ethanol 96% (VWR International GmbH, HiPerSolv CHROMANORM for HPLC, batch 19D234008) and further diluted with 2.7 mL water for injection (B Braun, batch 19041012). By further dilution with G5 (batch 19351015, 19222010) solutions of the concentration 0.10 mg/mL, 0.16 mg/mL, 0.18 mg/mL, 0.20 mg/mL, 0.22 mg/mL, 0.24 mg/mL and 0.30 mg/mL were achieved. Aliquots of the calibration standards were injected in triplicate. The calibration curve was constructed by plotting the peak area versus the nominal concentration of carmustine.
Intra- and inter-day accuracy and precision were validated by analysing carmustine solutions on five consecutive days. Stock solutions were freshly prepared as described above. Ten test solutions of the nominal concentration 0.2 mg/mL were obtained by mixing 60 µL stock solution and 940 µL G5 in HPLC vials. From test vials 1 and 10, samples were injected 10-fold on five consecutive days. From test vials 2–9, a single injection was performed on the same days.
pH measurement
The pH values were measured using a pH 210 Micoprocessor pH meter (Hanna Instruments, Kehl am Rhein, Germany) equipped with an InLab Micro pH glass electrode (Mettler Toledo, Greifensee, Germany). The pH meter was calibrated with standard buffer solutions pH 4.01 (DuraCal buffer, Hamilton Bonaduz AG; batch 1720122, expiry date 14 September 2021) and pH 7.00 (DuraCal buffer, Hamilton Bonaduz AG; batch 111005562, expiry date 22 April 2023) directly before each measurement time point. Each sample was measured once.
Osmolarity
Osmolarity of each sample was measured once by using an Osmomat 3000 D (serial number 300160266; Gonotec GmbH, Berlin, Germany).
Visual inspection
Test solutions were visually examined in normal laboratory light whenever samples were withdrawn. Test solutions with no colour change or any precipitation were defined as physicochemically stable.
Results
Validation of the RP-HPLC assay
The HPLC method was adopted from the stability-indicating method originally developed to analyse the bulk product and lyophilised powder of the licensed medicinal product.8 The correlation coefficient of the modified assay attained by plotting the peak areas against the corresponding concentrations amounted to R2=0.999 and proved linearity over the defined concentration range. The intra-day precision tests showed a mean carmustine concentration of 0.1965 mg/mL (98.25%)±0.66% relative standard deviation (RSD). The inter-day precision tests revealed a mean carmustine concentration of 0.1943 mg/mL (97.15%)±1.58% RSD. The results met the acceptance criteria based on ICH Q2 (R1)10 and proved reproducibility.
Stability of carmustine stock solutions and diluted infusion solutions
The HPLC chromatograms of the test solutions were consistently characterised by sharp peaks and retention times of about 7–8 min for the carmustine peak (see online supplemental figures 1 and 2). Peaks of related impurities and degradation products were not detected in the chromatograms during the stability tests. However, the peak area of the carmustine peak decreased rapidly in all test solutions prepared from the generic and the reference products. Detailed results regarding the loss of carmustine in the stock solutions and diluted infusion solutions during storage at 2–8°C and 22°C are shown in tables 3 and 4, respectively.
Table 3.
Stability of carmustine (Carmustin Obvius, Carmubris) stock solution stored for 48 hours at 2–8°C in the punctured vial and carmustine infusion solutions (0.2 mg/mL, 1.0 mg/mL) diluted in 5% glucose injection solution (freeflex PP/PE bags) stored at 2–8°C for 60 hours±further 6 hours stored at 22°C under light protection
| Carmustine-containing medicinal product | Initial carmustine concentration (mg/mL)±RSD (%) |
% Initial carmustine concentration remaining±RSD (%) (n=9) Measured concentration 0 hour=100% |
||||||
| Nominal | Measured | 12 hours | 24 hours | 48 hours | 60 hours | 60+3 hours | 60+6 hours | |
| Carmustin Obvius | 3.33 | 3.3707 (±0.57) | 98.46 (±1.52) | 96.87 (±1.11) | 94.02 (±2.31) | NA | ||
| Carmubris | 3.3481 (±0.93) | 99.61 (±0.68) | 97.89 (±0.47) | 95.45 (±0.76) | ||||
| Carmustin Obvius | 0.2 | 0.2011 (±1.39) | 96.84 (±0.60) | 95.42 (±0.39) | 93.03 (±0.22) | 91.95 (±0.40) | 89.82 (±0.49) | 86.80 (±0.29) |
| Carmubris | 0.1994 (±0.77) | 97.79 (±0.28) | 96.04 (±0.29) | 93.81 (±0.25) | 92.57 (±0.42) | 91.76 (±1.78) | 88.70 (±0.35) | |
| Carmustin Obvius | 1.0 | 0.9649 (±1,00) | NA | 96.39 (±0.83) | 95.47 (±0.56) | 93.07 (±0.67) | NA | |
The remaining carmustine concentration is expressed as mean±RSD percentage rate (%) of nine measurements per time point (n=9).
NA, not applicable; RSD, relative standard deviation.
Table 4.
Stability of carmustine (Carmustin Obvius, Carmubris) infusion solutions (0.20 mg/mL, 1.00 mg/mL) diluted in 5% glucose injection solution (freeflex PP/PE bags), stored at 22°C for 11 hours under light protection
| Carmustine-containing medicinal product | Initial carmustine concentration (mg/mL)±RSD (%) |
% Initial carmustine concentration remaining±RSD (%) (n=9) Measured concentration 0 hour=100% |
||||
| Nominal | Measured | 3.5 hours | 6 hours | 8.5 hours | 11 hours | |
| Carmustin Obvius | 0.2 | 0.2038 (±1.36) | 96.47 (±0.51) | 93.39 (±0.52) | 91.07 (±0.39) | 88.68 (±0.38) |
| Carmubris | 0.2045 (±1.16) | 96.08 (±0.31) | 93.57 (±0.49) | 91.36 (±0.30) | 88.88 (±0.32) | |
| Carmustin Obvius | 1.0 | 0.9855 (±1.28) | 96.41 (±0.86) | 94.59 (±0.64) | 92.14 (±0.76) | 89.99 (±0.69) |
The remaining carmustine concentration is expressed as mean±RSD percentage rate (%) of nine measurements per time point (n=9).
RSD, relative standard deviation.
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Immediately after reconstitution, the stock solutions of both products amounted to nearly 100% of the nominal carmustine content (specification 95–105%).9 The carmustine concentrations decreased to 94.02±2.31% (Carmustin Obvius) and 95.45±0.76% (Carmubris) after 48 hours storage under refrigeration. The in-use shelf life of the stock solutions of both products is therefore proven to be at least 48 hours when stored under refrigeration.
Carmustin Obvius 0.2 mg/mL and 1.0 mg/mL and Carmubris 0.2 mg/mL infusion solutions were found to be physicochemically stable for at least 60 hours when stored at 2–8°C, taking 90% of the initial concentration as acceptance criteria. Concerning the loss of carmustine, there was very little difference between the low and high concentration test solutions and also the undiluted stock solutions (see tables 3 and 4). After subsequent storage of the test solutions at 22°C for 3 hours, the carmustine concentrations averaged the 90% limit set and fell below the 90% limit after 6 hours (Carmustin Obvius 86.8%, Carmubris 88.7%). When the infusion solutions were stored at 22°C from the beginning, the carmustine concentrations were about 91% after 8.5 hours and fell below the 90% limit after 11 hours.
pH, osmolarity and visual inspection
The results of the pH measurements for test solutions stored at 2–8°C and 22°C are shown in tables 5 and 6, respectively.
Table 5.
pH of carmustine (Carmustin Obvius, Carmubris) stock solution stored for 48 hours at 2–8°C in the punctured vial and carmustine infusion solutions (0.20 mg/mL, 1.00 mg/mL) diluted in 5% glucose injection solution (freeflex PP/PE bags) stored at 2–8°C for 60 hours±further 6 hours stored at 22°C under light protection
| Carmustine-containing medicinal product | Concentration (mg/mL) | Mean±SD pH (n=3) | ||||||
| Initial | 12 hours | 24 hours | 48 hours | 60 hours | 60+3 hours | 60+6 hours | ||
| Carmustin Obvius | 3.33 | 5.91 (±0.41) | 5.76 (±0.28) | 4.84 (±0.08) | 4.62 (±0.07) | NA | ||
| Carmubris | 6.53 (±0.06) | 5.41 (±0.08) | 5.42 (±0.10) | 5.24 (±0.02) | ||||
| Carmustin Obvius | 0.2 | 6.77 (±0.13) | 6.51 (±0.05) | 6.41 (±0.06) | 6.39 (±0.08) | 6.28 (±0.02) | 6.08 (±0.07) | 6.21 (±0.19) |
| Carmubris | 6.79 (±0.10) | 6.57 (±0.10) | 6.17 (±0.22) | 6.37 (±0.12) | 5.42 (±0.15) | 5.62 (±0.09) | 4.98 (±0.15) | |
| Carmustin Obvius | 1.0 | 6.67 (±0.17) | NA | 6.08 (±0.07) | 5.57 (±0.14) | 5.55 (±0.20) | NA | |
Mean±SD pH of three measurements per sample per time point (n=3).
NA, not applicable.
Table 6.
pH of carmustine (Carmustin Obvius, Carmubris) infusion solutions (0.20 mg/mL, 1.00 mg/mL) diluted in 5% glucose injection solution (freeflex PP/PE bags), stored at 22°C for 11 hours under light protection
| Carmustine-containing medicinal product | Concentration (mg/mL) | Mean±SD pH (n=3) | ||||
| Initial | 3.5 hours | 6 hours | 8.5 hours | 11 hours | ||
| Carmustin Obvius | 0.2 | 6.59 (±1.31) | 5.32 (±6.51) | 6.23 (±1.54) | 5.36 (±5.10) | 6.11 (±5.50) |
| Carmubris | 4.90 (±6.98) | 4.91 (±6.21) | 5.25 (±2.38) | 4.92 (±4.22) | 4.82 (±4.63) | |
| Carmustin Obvius | 1.0 | 6.18 (±1.18) | 5.77 (±2.23) | 5.75 (±1.25) | 5.57 (±1.67) | 5.36 (±3.82) |
Mean±RSD pH of three measurements per sample per time point (n=3).
RSD, relative standard deviation.
The initial pH values of the stock solutions were 5.9 for Carmustin Obvius and 6.5 for Carmubris. For both products, the measured pH values are higher than the indicated ones (Carmustin Obvius 4.0–5.0,1 Carmubris 5.6–6.02). The pH values of the stock solutions of both brand products fell continuously over a period of 48 hours (Carmustin Obvius pH 4.6, Carmubris pH 5.2). In addition, the initial pH values of the diluted infusion solutions surpassed pH 6, and also decreased over the observation period in test solutions of both medicinal products.
Measurement of the osmolarity showed that both products fulfilled the acceptance criteria of the official documents. No changes in osmolarity were registered during the observation period for stock solutions (∼1900 mOsm/L) or for infusion solutions (∼380 mOsm/L) of both manufacturers and for all storage temperatures. No visible particles or colour changes were found at any time.
Discussion
Experimental conditions
The storage conditions were chosen according to the in-use shelf life given in the Summary of Product Characteristics (SmPC) and practicality issues in a pharmacy-based cytotoxic reconstitution area. Therefore, stock solutions and diluted ready-to-administer infusion solutions were stored refrigerated, in accordance with common pharmacy practice. In order to simulate the administration procedure at room temperature, stability of the light-protected infusion solutions was studied at 22°C in a climatic chamber.
Acidic and especially base-induced decomposition of carmustine in aqueous media is described.3 4 11 Carmustine is most stable in aqueous buffered solutions in pH ranges from minimum 3.5 to maximum 5.0.3 4 Above pH 7, carmustine undergoes more rapid decomposition.11 The pH of marketed G5 infusion solutions is usually lower than the pH of 0.9% NaCl solutions, thus favouring the stability of carmustine.5 Therefore, diluted infusion solutions were prepared by using prefilled G5 infusion bags (pH 4.3) as diluent solutions. Instead of glass containers, inert polyolefin bags (PP/PE) were used. Because of occupational safety, plastic containers are to be preferred and the suitability of PE containers is indicated for the generic product.1 5 6 Laskar and Ayres3 reported sorption of carmustine to polyvinylchloride, ethylene-vinyl acetate and polyurethane administration sets, but not to PE or glass surfaces. Significant sorption and incompatibility with the primary container were not expected. An administration set was not connected, and samples were directly withdrawn from the container.
Carmustine is relatively light-sensitive.4 Therefore, the test solutions were stored in an opaque plastic box and only exposed to fluorescent light during sampling. In clinical practice, light protection is ensured by covering the containers with lightproof bags and using opaque administration sets to avoid light-induced degradation.
Physicochemical stability
Carmustine decomposes in aqueous solution to form 2-chloroethylamine hydrochloride, acetaldehyde, nitrogen and carbon dioxide.12 Because these degradation products are not absorbing UV light, degradation peaks were not traceable in the HPLC spectra. Further, the originator indicates that the reconstituted injection decomposes by zero order kinetics.13 At ambient and refrigerated temperatures, the anticipated loss is 6% in 3 hours and 4% in 24 hours, respectively. In our studies the loss of carmustine amounted to about 3% in 3 hours at 22°C and about 3% in 24 hours at refrigerated temperatures. The observed degradation rates at ambient temperature and the recommended infusion period of 1–2 hours limit the storage period of the infusion solutions at temperatures above 20°C and may result in carmustine concentrations lower than 90% when the infusion is completed. Of note, the remaining carmustine content of the generic product was equivalent to that reported by other investigators for the reference product.5 6
The rate of degradation is considered to be independent of the carmustine concentration. Loss of carmustine was slightly higher in the more diluted infusion solutions (0.2 mg/mL) in both temperature conditions. Eventually, sorption of lipophilic carmustine to the surface of the infusion bag becomes obvious when the concentration is lower and results in a higher sorption percentage rate. However, the effect seems to be minimal in PE bags and is likely to be irrelevant in clinical practice.7
It is noteworthy that the indicated pH values of the reconstituted generic and reference products differ by one pH unit although the solvents and excipients are identical (see table 1). Measured pH values of the reconstituted stock solutions and of the diluted carmustine infusion solutions were higher than indicated in the official documents. As the pharmaceutical form is a powder or a lyophilisate, this might be the reason why different pH values were measured after dissolution. Like Ostermann-Kraljevic et al,7 we found that the decrease in pH is more intensive when the carmustine concentration is higher. This can be explained by the increased formation of acidic degradation products (eg, acetaldehyde).
Although the measured pH values were higher than those favouring stability,3 4 physicochemical stability was not reduced in our experiments. A limitation of our study is that we did not test 0.9% NaCl infusion solutions as a vehicle solution. However, we assume that the differing pH values of pure G5 (pH 4.3) and 0.9% NaCl infusion solutions (pH 5.98 declared pH 5.0–7.0) do not affect the pH of the admixtures and the physicochemical stability of carmustine infusion solutions to a relevant extent.
By using the same solvents, diluents and primary containers, equivalent degradation kinetics for the reference and generic medicine were found. Although PP/PE bags were used instead of glass containers, in our experiments the stability time of the diluted infusion solutions was longer than the in-use stability time given in the SmPCs of both medicinal products.
Conclusion
Identical carmustine losses were found in stock solutions and infusion solutions prepared in G5 polyolefin bags of the generic product (Carmustin Obvius) and the reference product (Carmubris). Degradation kinetics were shown to be independent of the initial concentration of carmustine. According to the physicochemical stability data, the shelf life (95% limit) of the refrigerated stock solution was 48 hours and the shelf life (90% limit) of the ready-to-administer infusion solution was 60 hours at 2–8°C or 8.5 hours at 22°C under light protection. These results facilitate the use of both medicinal products in a pharmacy-based centralised cytotoxic preparation unit.
What this paper adds.
What is already known on this subject
The degradation of reconstituted and diluted carmustine-containing infusion solutions depends on pH, temperature and light.
The physicochemical stability of the reconstituted and diluted carmustine originator product (Carmubris) was determined by HPLC assays and pH measurement.
What this study adds
Physicochemical stability data of the reconstituted and diluted carmustine generic product (Carmustin Obvius) stored in a refrigerator or at room temperature.
Carmustin Obvius and Carmubris reconstituted stock solutions are physicochemically stable for at least 48 hours when stored at 2–8°C.
Carmustin Obvius and Carmubris infusion solutions 0.2 mg/mL or 1 mg/mL are physicochemically stable for at least 8.5 hours and 60 hours when stored at 22°C and 2–8°C, respectively.
Footnotes
Contributors: LK carried out the experiments, analysed the data and wrote the manuscript. IK supervised the project and checked the manuscript together with JT.
Funding: The laboratory tests were funded by a specific grant of Medac GmbH, Wedel, Germany. The company had no influence on the results presented in the manuscript.
Competing interests: None declared.
Provenance and peer review: Not commissioned; externally peer reviewed.
Supplemental material: This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.
Data availability statement
All data relevant to the study are included in the article or uploaded as supplementary information. The data that support the findings of this study are available from the corresponding author, LK, upon reasonable request.
Ethics statements
Patient consent for publication
Not required.
References
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
ejhpharm-2020-002597supp001.pdf (23.8KB, pdf)
ejhpharm-2020-002597supp002.pdf (23.8KB, pdf)
Data Availability Statement
All data relevant to the study are included in the article or uploaded as supplementary information. The data that support the findings of this study are available from the corresponding author, LK, upon reasonable request.