Degradation of carmustine in aqueous media

Physicochemical stability of carmustine-containing medicinal products after reconstitution and after dilution to ready-to-administer infusion solutions stored refrigerated or at room temperature

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.

Voltammetric and amperometric determination of N-nitroso antineoplastic drugs at mercury and amalgam electrodes

A hanging mercury drop electrode and a mercury meniscus modified silver solid amalgam electrode were used as electroanalytical sensors for voltammetric determination of antineoplastic drugs carmustine, lomustine and streptozotocin containing reducible N-nitroso groups. On the example of carmustine it was shown that its one-step reduction proceeds at substantially more negative potentials at amalgam electrode as compared with mercury electrode. Both electrodes offer satisfactory repeatability of current response (relative standard deviations < 5%) using DC voltammetry and differential pulse voltammetry. The achieved limits of determination lie mostly in the 10–7 mol l–1 concentration range. The mentioned voltammetric methods were applied to determination of carmustine and lomustine in pharmaceutical formulations. Further, the mercury meniscus modified silver solid amalgam electrode was employed in a “wall-jet” amperometric detection cell in the determination of carmustine by flow injection analysis. Under optimized conditions (run electrolyte Britton– Robinson buffer of pH 7.0; flow rate 5.5 ml min–1; detection potential –1.5 V; injection volume 0.02 ml) the limit of quantitation 7.1 × 10–6 mol l–1 was achieved.

Polyanhydride degradation and erosion

It was the intention of this paper to give a survey on the degradation and erosion of polyanhydrides. Due to the multitude of polymers that have been synthesized in this class of material in recent years, it was not possible to discuss all polyanhydrides that have gained in significance based on their application. It was rather the intention to provide a broad picture on polyanhydride degradation and erosion based on the knowledge that we have from those polymers that have been intensively investigated. To reach this goal this review contains several sections. First, the foundation for an understanding of the nomenclature are laid by defining degradation and erosion which was deemed necessary because many different definitions exist in the current literature. Next, the properties of major classes of anhydrides are reviewed and the impact of geometry on degradation and erosion is discussed. A complicated issue is the control of drug release from degradable polymers. Therefore, the aspect of erosion-controlled release and drug stability inside polyanhydrides are discussed. Towards the end of the paper models are briefly reviewed that describe the erosion of polyanhydrides. Empirical models as well as Monte-Carlo-based approaches are described. Finally it is outlined how theoretical models can help to answer the question why polyanhydrides are surface eroding. A look at the microstructure and the results from these models lead to the conclusion that polyanhydrides are surface eroding due to their fast degradation. However they switch to bulk erosion once the device dimensions drop below a critical limit.

Comparative effects of (SBE)7m-beta-CD and HP-beta-CD on the stability of two anti-neoplastic agents, melphalan and carmustine

The purpose of this study was to evaluate and compare the potential use of two parenterally safe beta-cyclodextrins derivatives, (SBE)7m-beta-CD and HP-beta-CD, as solubilizers and stabilizers for melphalan and carmustine, two very unstable antineoplastic agents. Phase solubility and chemical stability of the compounds in the presence of the cyclodextrins were studied. UV, fluorescence, and several NMR techniques were used to probe the potential causes for the differences observed. The phase solubility method was found to provide only qualitative data on the binding of melphalan to the cyclodextrins since rapid degradation and the presence of products of degradation complicated the interpretation of the results. Qualitatively, however, the solubilizing potential was similar for the two cyclodextrins. The chemical stability studies indicate that both of the drugs had similar binding constants for both cyclodextrins; however, the intrinsic reactivities in the complexes were significantly lower with (SBE)7m-beta-CD than for HP-beta-CD. The main cause for this distinct difference appeared to correlate with differences in the site of binding and the polarity of the binding site.

BCNU stability as a function of ethanol concentration and temperature

BCNU is increasingly used in low ethanol (ETOH) concentrations, 5% dextrose-water (D5W), or normal saline (NS) solutions, especially for intra-arterial and prolonged (e.g., 3 day) intravenous (IV) infusions. Little work, however, has been done to evaluate BCNU decomposition rates in concentrations, diluents, and temperatures similar to those employed clinically. This study examined BCNU solutions in ETOH, NS, and D5W to evaluate, conclusively, initial recovery and decomposition rates in these three diluents. Initial BCNU recovery rates were: 95.6 +/- 0.3% (100% D5W), 89.6 +/- 0.5% (15% ETOH), and 85.2 +/- 0.5% (NS) (P less than 0.001). Study of all solutions revealed no measurable BCNU decomposition over 24 hrs (0 degrees C) and no significant difference in decomposition rates between any of the diluents (19.5 degrees C). At 37 degrees C, the solutions showed different half-lives: 14.3 +/- 0.19 hrs (15% ETOH), 10.6 +/- 0.02 hrs (10% ETOH), 8.2 +/- 0.21 hrs (5% ETOH), 7.3 +/- 0.06 hrs (NS), and 6.8 +/- 0.07 hrs (D5W) (P less than 0.001). Decomposition rates between all three temperatures (19.5 degrees C, 37 degrees C, and 50 degrees C) were significantly different (P less than 0.01) for each diluent. Dissolving BCNU powder into either D5W or NS required only 5 min when hand-shaken at body temperature. This study of initial recovery and decomposition rates suggests that, although BCNU decomposition rates were significantly increased at body temperature (37 degrees C), it was quite low and essentially unaffected by different diluents at room temperature (i.e., 19.5 degrees C).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of carbamoylating agents on tumor metabolism

Carbamoylation of macromolecules occurs by the displacement of hydrogen on several groups, but the most stable addition at neutral pH is on amino groups. This reaction occurs predominantly with proteins and results from the administration in vivo of inorganic cyanate or organic isocyanates. The latter act more rapidly, but also are more rapidly hydrolyzed in aqueous solution. This instability has been a factor limiting study of the pharmacological properties of organic isocyanates. However, organic isocyanates are released from some nitrosoureas of value in cancer therapy such as 1,3-bis(2-chlorethyl)-1-nitrosourea (BCNU) and 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU). The carbamoylating activities of BCNU and CCNU are generally considered less significant than their alkylating activity in the action of these drugs on tumors, but carbamoylation may serve to inhibit DNA repair. There is evidence that carbamoylating agents can exert selective inhibitory effects on metabolite uptake and macromolecular synthesis in neoplastic tissues. Such selectivity is much more notable in vivo than in vitro. In the case of cyanate, the selectivity in vivo has been variously attributed to a requirement for metabolic activation, to selective effects on circulation in solid tumors, and to diminished pH in tumors. It is the distinction between such factors and the identification of critical cellular targets which provide major challenges in present studies on the effects of carbamoylating agents on tumor metabolism.

pH-induced modification of BCNU toxicity on glial cells

A dose-response relationship for the dependence of the cytotoxic activity of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) on extracellular pH has been established. The hypothesis, that the integral dose of the rapidly degrading BCNU determines cytotoxicity, has been examined. Human glial cells exhibited lower survival rates for BCNU exposure at pH 6.5 and pH 6.7, compared to pH 7.4. This effect can be explained by the more rapid decay of BCNU at pH 7.4, leading to a lower integral dose. However, the determination of BCNU decay constants for different pH values and calculation of the integral exposure dose reveal that tolerance to BCNU is increased with decreasing pH.

Stability of solutions of antineoplastic agents during preparation and storage for in vitro assays. General considerations, the nitrosoureas and alkylating agents

In vitro drug sensitivity of tumour biopsies is currently being determined using a variety of methods. For these chemosensitivity assays many drugs are required at short notice, and this in turn means that the drugs must generally be stored in solution. There are, however, a number of potential problems associated with dissolving and storing drugs for in vitro use, which include (a) drug adsorption; (b) effects of freezing; (c) drug stability under the normal conditions of dilution and setting up of an in vitro assay; and (d) insolubility of drugs in normal saline (NS) or phosphate-buffered saline (PBS). These problems are considered in general, and some recommendations for use of solutions of drugs in in vitro assays are suggested. The nitrosoureas and alkylating agents are also investigated in greater detail in this respect. The nitrosoureas are found to be very labile in PBS at pH 7, with 5% degradation (t0.95) occurring in 10-50 min at room temperature. These values are increased about 10-fold on refrigeration and about 5- to 10-fold on reduction of the pH of the medium to pH 4-5. At pH 7 and room temperature, t0.95 is observed in under 1 h with the alkylating agents nitrogen mustard, chlorambucil, melphalan, 2,5-diaziridinyl-3,6-bis(2-hydroxyethylamino)-1,4-benzoquinone (BZQ), dibromodulcitol, dibromomannitol, treosulphan, and procarbazine. Of the other alkylating agents, 4-hydroperoxycylophosphamide (sometimes used in vitro in place of cyclophosphamide), busulphan, dianhydrogalactitol, aziridinylbenzoquinone (AZQ), and dacarbazine have a t0.95 of between 2 and 24 h, while ifosfamide and pentamethylmelamine are both stable in aqueous solution for greater than 7 days. About half the drugs studied in detail have been stored frozen in solution for in vitro use, although very little is known about their stability under these conditions.

Tumor cell anti-oxidant defenses. Inhibition of the glutathione redox cycle enhances macrophage-mediated cytolysis

The basis of resistance to oxidative injury was studied in six murine tumor cell lines that differed 54-fold in their resistance to enzymatically generated H(2)0(2). The tumors varied 56.7-fold in their specific activity of catalase, 5.3-fold in glutathione peroxidase (GPO), 3.3-fold in glutathione reductase (GR), and 2.7-fold in glutathione. There was no correlation among the levels of the three enzymes, and tumor cell resistance to lysis by H(2)0(2). However, the logarithm of the flux of H(2)0(2) necessary to cause 50 percent lysis of the tumor cells correlated with their content of glutathione (r = 0.91). The protective role of glutathione was analyzed by blocking GR and GPO, the catalysts of the glutathione redox cycle. This was facilitated by the demonstration that the anti-neoplastic agent 1,3-bis-(2- chloroethyl)-l-nitrosourea (BCNU) was a potent inhibitor of GR in intact tumor cells. BCNU inactivated tumor cell GR with a 50 percent inhibitory dose of 11 muM and a t(l/2) of inhibition of 30 s. Complete inhibition of GR was attained with no effect on GPO or catalase. Tumor cells whose GR was inactivated by BCNU could be lysed by fluxes of H(2)0(2) to which they were otherwise completely resistant. They could be killed by phorbol myristate acetate (PMA)-stimulated, bacilli Calmette-Guerin-activated macrophages in numbers which were otherwise insufficient, and by nonactivated macrophages, which otherwise were ineffective. BCNU-treated target cells were also much more sensitive to antibody-dependent, macrophage-mediated cytolysis. However, such tumor cells were no more sensitive than controls to lysis by alloreactive T cells or by antibody plus complement. Next, we deprived tumor cells of selenium by passage in selenium-deficient mice. GPO was inhibited 85 percent in such cells, with no effect on GR or catalase. Tumor cells with reduced GPO activity were markedly sensitized to lysis by small fluxes of H(2)0(2) or by PMA-stimulated macrophages or granulocytes. In contrast, inhibition of catalase with aminotriazole had no effect on the sensitivity of three tumors to peroxide-mediated lysis, and had modest effects with two others. Thus, the oxidation-reduction cycle of glutathione serves as one of the major defense mechanisms of tumor cells against three related forms of oxidant injury: lysis by fluxes of H(2)0(2), by PMA-triggered macrophages, and by macrophages in the presence of anti-tumor antibody.

Mechanism of hydrolysis of halogenated nitrosoureas

The hydrolysis kinetics of halogenated nitrosoureas were investigated using chlorozotocin as a model. Evidence is presented to show that the hydrolytic reaction of halogenated nitrosoureas between pH 3 and 8 is a summation of spontaneous water and hydroxide-ion-catalyzed reactions; the later reaction is the sum of two parallel reactions. The relative contribuiton of each reaction changes with pH and results in different product distributions. Dianionic phosphate (HPO42-) increased the amount of free chloride-ion production without significantly altering the hydrolysis rate. A mechanism is proposed to explain this behavior. The role of hydrolytic decomposition products produced at physiological pH on the biological activity of nitrosoureas is discussed.

Degradation of carmustine in mixed solvent and nonaqueous media

The degradation rate of carmustine in several solvent mixtures and in mannitol solution was investigated at 5, 22, and 37 degrees. The solvents chosen were those utilized as parenteral diluents. The apparent first-order degradation rate constants were computed using a linear regression procedure. The most nonaqueous solvent mixtures demonstrated minimum apparent degradation rates. The apparent degradation rate constant decreased with a decrease in the macroscopic dielectric constant. From the data at several temperatures, the apparent activation energies for carmustine degradation in the several solvent mixtures were calculated. There was no evidence for a relationship between the apparent activation energy and the dielectric constant.