Unité de Pharmacologie Cellulaire et Moléculaire, Université Catholique de Louvain, UCL 73.70 avenue E. Mounier 73, B-1200 Brussels, Belgium
Received 25 July 2002; returned 19 October 2002; revised 24 November 2002; accepted 24 December 2002
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Abstract |
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Keywords: stability, continuous infusion, degradation, compatibility
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Introduction |
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Materials and methods |
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All conditions were aimed at mimicking the use of cefepime by continuous infusion in cystic fibrosis and intensive care patients. Based on the most accepted susceptibility breakpoint for cefepime (8 mg/L), a stable serum concentration of at least 2040 mg/L was considered desirable,3 meaning a daily dose of up to 6 g. Anticipated clinical practice implied that this daily dose would be placed in a single container (typically a 48 mL syringe, as used in commercially available motor-operated syringe pumps for intensive care patients, or a 125 mL motor-less elastomeric pump carried under clothes for cystic fibrosis patients), which would be left in place for a 24 h period. This led us to set the drug concentration in a 512% (w/v) range. After having determined that maintaining either cefepime or ceftazidime in solution at 37°C for more than a few hours caused appreciable degradation, we systematically investigated the 2030°C (6886°F) temperature range, which is the most frequently encountered in intensive care units. Compatibility studies were designed to take into account the situation most likely to cause unnoticed adverse effects, i.e. the ß-lactam and another medication infused from distinct containers but through a common line using a Y-shaped connector. The drugs tested were selected based on a survey identifying those most frequently used via the intravenous route in intensive care patients in Belgium. These premises led us to adopt the methods described here.
Preparation of solutions and condition of storage
All solutions of cefepime and ceftazidime were freshly prepared using commercially available compounds. Dissolution was in water obtained from a Milli-Q Academic Ultrapure Water System (Millipore Corp., Bedford, MA, USA). No addition of NaCl or glucose was deemed necessary since the solutions were highly hypertonic. The solutions equilibrated spontaneously at pH 4.8 for cefepime, and at
pH 7 for ceftazidime. No pH adjustment was attempted since: (i) preliminary studies, as well as private (during the review process of this paper, the Bristol-Myers Squibb Company communicated to one of us unpublished data on the pHrate profile of cefepime degradation at 35°C, showing a typical U-shaped profile with maximum stability at
pH 45) and published data,17 showed that these conditions provided optimal stability; and (ii) no commercially available and/or pharmaceutically validated means of adjusting the pH of such concentrated solutions is presently available to the clinician. In the case of ceftazidime, for which the commercially available form contains sodium carbonate (118 mg/g of ceftazidime) and is stored in a CO2-containing vial, care was taken to avoid CO2 release and subsequent change of pH by running all experiments in closed and completely filled vials.
Compatibility studies
Each drug was prepared in solution (or diluted if supplied in solution) exactly as recommended for hospital usage in the corresponding Belgian Notice Scientifique18 [i.e. the Summary of Product Characteristics (SPC) or following the corresponding suppliers documentation]. The final concentration and rate of infusion of each drug were those corresponding to recommendations for use in intensive care patients. The rate of infusion of the ß-lactam (12% w/v) was set up at 2 mL/h. Based on these considerations, we calculated the concentrations of the antibiotic and of the co-administered drug that would be reached in the common line of the Y-shaped infusion set. Appropriately dosed mixtures were then prepared and left standing at 25°C for 1 h before being examined for physical compatibility. The latter was assessed by visual inspection using an LV 28 Liquid Viewer (P. W. Allen and Co. Ltd, Tewkesbury, UK) in comparison with a pure solution of cefepime (or ceftazidime) and distilled water. All mixtures showing visible signs of precipitation were considered as demonstrating physical incompatibility [and the presence of particles thereafter confirmed by light scattering analysis; Sub Micron Particle Analyser COULTER N 4 MD (Coulter Corp., Miami, FL, USA)]. All mixtures with no sign of precipitation were examined for their content of the corresponding ß-lactam using HPLC analysis, and were considered as demonstrating chemical stability if the ß-lactam concentration had not fallen below 90% of its nominal content.
Determination of cefepime and ceftazidime concentrations
We used a published HPLC method19 with the following specific conditions: X-terra RP 18 column; elution buffer, 10 mM sodium acetate buffer pH 5/acetonitrile (95:5 v/v); flow rate 1 mL/min; UV detector, 258 nm for cefepime and 254 nm for ceftazidime. All analyses were made with a Waters 2690 System (Waters Corp., Milford, MA, USA) equipped with diode array detector and operated with the proprietary Waters Millennium 32 software. Assays showed linearity from 1 to 200 mg/L [r2 = 0.99; maximal coefficient of variation (based on the repetition of at least 30 determinations of the same samples), 4%]. All measurements were made against freshly prepared quality control solutions run with each series of assays. Each sample was assayed at least three times and the data pooled.
Other studies
pH was measured with an MP 225 pH meter (Metler-Toledo AG, Schwerzenbock, Switzerland) with calibration at each of the temperatures used. Absorbance spectra were obtained with a UVIKON 933 Double Beam UV/VIS Spectrophotometer (Bio-Tek Instruments Inc., Winooski, VT, USA) over a wavelength range of 200800 nm and at a scan speed of 200 nm/min.
Materials
Cefepime was supplied by Bristol-Myers Squibb Belgium and ceftazidime by GlaxoSmithKline Belgium as the original, branded products (MAXIPIME and GLAZIDIM, respectively). All other drugs were obtained through the Hospital Pharmacy as the registered commercial product for parenteral use. Each drug was supplied by the corresponding marketing authorization holder of the original, branded product and complied with the Belgian or other applicable Pharmacopoeia. All products for chromatography were of HPLC grade and obtained from SigmaAldrich Corp. (Steinheim, Germany) or E. Merck AG (Darmstadt, Germany).
Statistical analyses
All experiments were carried out in triplicate (independent experiments), and all data points used to calculate means and standard deviations (S.D.). Two-way ANOVA analysis was carried out with the significance level set at 5%.
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Results |
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In this first series of experiments, solutions of cefepime and ceftazidime were prepared at increasing concentrations from 5% to 12% and systematically exposed at fixed temperatures ranging from 20 to 37°C for increasing periods of time. Cefepime remained >95% stable at 20°C for up to 24 h at all concentrations but was unstable at 37°C (>10% degradation within 12 h) whatever its concentration (in the range studied). We therefore examined in more detail the influence of the temperature for 25°C and 30°C, which are of direct clinical interest. Figure 1 shows indeed that this range is critical since the loss of cefepime reached 10% within 24 h at 25°C (which is the limit set up for ceftazidime solutions by the US Pharmacopeia;20 note that neither the US nor the European Pharmacopoeia sets limits of degradation for cefepime in solution), and markedly exceeded this limit if incubation was carried out at 30°C. A two-way ANOVA analysis of the data presented in Figure 1 showed that cefepime and ceftazidime did not share a common behaviour, with ceftazidime demonstrating globally a greater stability at both 25°C (P = 0.04) and 30°C (P = 0.01). Meaningful differences were, however, only seen at 24 h for incubations at 25°C, and at 16 h for incubations at 30°C.
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A marked difference was noted between cefepime and ceftazidime, with cefepime solutions showing a marked increase in pH progressing over time after an initial lag period of 812 h. This change was temperature dependent. In contrast, almost no change in pH was seen with ceftazidime. Figure 2 shows typical results obtained at 37°C (with respect to time; this temperature was chosen to demonstrate clearly the characteristic lag period) and at 24 h (with respect to temperature) using a fixed concentration for both drugs (12%; less concentrated solutions were more susceptible to pH change due to the reduced buffering capacity of these diluted solutions). Again, no marked change in pH was seen with ceftazidime under similar conditions.
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Freshly prepared solutions of cefepime display a light yellow colour that, according to the Belgian SPC,18 must be considered normal for all cephalosporins and may change gradually to amber yellow without loss of activity. Yet, we noted that the solutions of cefepime turned to redpurple if kept at 30°C for 1216 h, whereas the solutions of ceftazidime remained yellowamber. Spectrophotometry was therefore used to better characterize this change. Whereas complete scans from 200 to 800 nm were made, significant changes were seen only in the 420550 nm range. The corresponding spectra are shown in Figure 3 for 12% solutions kept at 30°C for 16 and 24 h in comparison with that of freshly prepared solutions (0 h). Whereas only a low absorbance in the 420440 nm region (corresponding to a pale yellow colour) was seen with unincubated solutions, a marked absorbance with a maximum at 490 nm (red) was noted at 16 h for cefepime. At 24 h, the absorbance of cefepime solutions had still increased and shifted to a maximum at 500 nm (redpurple). At the same time, the absorbance at 420440 nm had completely disappeared. Figure 3 shows that these changes were much less marked with ceftazidime. In additional experiments, we observed that the change in colour of cefepime solutions was dependent upon the initial drug concentration and temperature (data not shown).
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All initial studies were carried out using a 12% solution for both cefepime and ceftazidime and the corresponding results are presented in summary in Table 1. Among all antimicrobials tested, only erythromycin was incompatible with both cefepime and ceftazidime, whereas clarithromycin and vancomycin were incompatible with ceftazidime only. For all other drugs tested, incompatibilities were common to both cefepime and ceftazidime but the nature of the incompatibility (i.e. physical versus chemical) was sometimes different (for instance, incompatibility with midazolam was of a chemical nature for cefepime but of a physical nature for ceftazidime). The most severe chemical incompatibility was noted with theophylline (up to 25% degradation of cefepime after 1 h of contact). With respect to physical incompatibility, all samples showing visual evidence of precipitation also gave consistent readings when examined in an automatic particle analyser (data not shown). All these incompatibilities were concentration independent (within a range of clinically meaningful concentrations), except for dobutamine, for which concentrated solutions (250 mg/mL, as used for bolus administration) proved physically incompatible, whereas diluted solutions (1 mg/mL, as used for continuous infusion) showed neither physical nor chemical signs of incompatibility.
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Discussion |
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Whatever the chemical details of the degradation of cefepime, the present study also shows unambiguously that cefepime (or ceftazidime) cannot be administered by continuous infusion in cystic fibrosis patients with pumps carried under clothes, since the temperature of the solution is likely to exceed 2530°C (recent data based on Arrhenius plot analyses show that 29.1°C is the upper limit for ensuring 90% cefepime intactness over 24 h).28 These devices will therefore need to be changed at least every 8 h. Clear warnings must therefore be voiced in this context since clinical investigators seem to have ignored the potentially dangerous degradation of ceftazidime under these conditions.7 Our warning needs to be even stronger for cefepime in view of the liberation of the so far unidentified degradation products as described above.
Moving now to the use of continuous infusion of cefepime and ceftazidime in intensive care units, it must be stressed that both drugs ought to be kept at temperatures preferably not exceeding 25°C. Effective control of the temperature in clinical wards will therefore be essential. Here also, additional warning must be given concerning cefepime in the absence of additional chemical studies concerning the nature of its degradation products. The occurrence of clinical signs of neurotoxicity in renally impaired patients receiving cefepime and other ß-lactams without appropriate dosing corrections (see reference 36 for a recent report) raises questions in this context even though a cause to effect relationship has not been demonstrated.
Finally, our studies on drug compatibility indicate definite limitations in the routine use of continuous infusion with either cefepime or ceftazidime. It must be emphasized that chemical incompatibilities have not been characterized here beyond the mere observation of a decreased content of cefepime or ceftazidime in the solutions. The nature of the chemical compounds formed therefore needs to be studied in detail. Yet, it is clear that the incompatibilities seen here are more numerous than those mentioned in the official SPCs. The latter also contain information that varies between countries [and sometimes in a contradictory fashion; for instance, the official US Product Information (approved labelling)29 for cefepime mentions incompatibilities with vancomycin, gentamicin, tobramycin and theophylline, whereas the official Belgian Notice Scientifique18 mentions only gentamicin as being incompatible but lists theophylline as compatible]. For ceftazidime, only vancomycin incompatibility is listed in both SPCs and has been published as such.37 These inconsistencies and the differences with our observations stem most likely from the fact that studies made in support of registration and used for establishing SPCs have not specifically considered the conditions under which continuous infusion would be implemented in the clinical arena as has been done here. As well as providing direct information to clinicians in this context, our data also illustrate the necessity of examining carefully the conditions of use of ß-lactams if deviating from the originally foreseen and officially approved modes of administration.
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Acknowledgements |
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Footnotes |
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References |
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