The Structural Role of N170 in Substrate-Assisted Deacylation in KPC-2 β-Lactamase

The amino acid substitutions in Klebsiella pneumoniae carbapenemase 2 (KPC-2) that have arisen in the clinic are observed to lead to the development of resistance to ceftazidime-avibactam, a preferred treatment for KPC bearing Gram-negative bacteria. Specific substitutions in the omega loop (R164-D179) result in changes in the structure and function of the enzyme, leading to alterations in substrate specificity, decreased stability, and more recently observed, increased resistance to ceftazidime/avibactam. Using accelerated rare-event sampling well-tempered metadynamics simulations, we explored in detail the structural role of R164 and D179 variants that are described to confer ceftazidime/avibactam resistance. The buried conformation of D179 substitutions produce a pronounced structural disorder in the omega loop - more than R164 mutants, where the crystallographic omega loop structure remains mostly intact. Our findings also reveal that the conformation of N170 plays an underappreciated role impacting drug binding and restricting deacylation. The results further support the hypothesis that KPC-2 D179 variants employ substrate-assisted catalysis for ceftazidime hydrolysis, involving the ring amine of the aminothiazole group to promote deacylation and catalytic turnover. Moreover, the shift in the WT conformation of N170 contributes to reduced deacylation and an altered spectrum of enzymatic activity.

Simultaneous determination of ceftazidime and pyridine in human plasma by LC-UV

A sensitive, accurate and precise liquid chromatography (LC) method for the simultaneous determination of ceftazidime and pyridine in human plasma has been developed and validated. Acetonitrile (ACN) was employed to precipitate the proteins in the plasma samples. Chromatographic separation was performed with a Kinetex® C18 (150 mm × 3 mm, 2.6 µm) column with gradient elution. Ammonium formate 20 mM and ACN were mixed in a ratio of 98:2 (v/v) for mobile phase A and 85:15 (v/v) for mobile phase B. Both were adjusted to pH 4.5 with formic acid. The flow rate was 0.4 mL/min. UV detection was performed at 254 nm. Calibration curves were linear in the range from 0.3 to 225 μg/mL for ceftazidime and from 0.2 to 10 μg/mL for pyridine with correlation coefficients ≥ 0.999. Within- and between-run precision and accuracy were satisfactory with coefficients of variation (CV) ≤ 8.0% and deviations ≤ 7.0%, respectively. The method fulfilled all validation criteria prescribed by the European Medicines Agency guidelines. Next, it has been used successfully to analyze plasma samples of patients who received ceftazidime under intermittent and continuous administration. With intermittent administration, the concentration of the antibiotics reached a peak and then dropped quickly, which may be below the minimal inhibitory concentration (MIC). With continuous administration, the concentration of the antibiotics remained stable over 24 h, certainly above the MIC. Although the same tendency in ceftazidime concentration changes over time was observed, a difference in concentration amongst the patients was noticeable. The concentration of pyridine in plasma was negligible.

Sustained Release of Antifungal and Antibacterial Agents from Novel Hybrid Degradable Nanofibers for the Treatment of Polymicrobial Osteomyelitis

This study aimed to develop a drug delivery system with hybrid biodegradable antifungal and antibacterial agents incorporated into poly lactic-co-glycolic acid (PLGA) nanofibers, facilitating an extended release of fluconazole, vancomycin, and ceftazidime to treat polymicrobial osteomyelitis. The nanofibers were assessed using scanning electron microscopy, tensile testing, water contact angle analysis, differential scanning calorimetry, and Fourier-transform infrared spectroscopy. The in vitro release of the antimicrobial agents was assessed using an elution method and a high-performance liquid chromatography assay. The in vivo elution pattern of nanofibrous mats was assessed using a rat femoral model. The experimental results demonstrated that the antimicrobial agent-loaded nanofibers released high levels of fluconazole, vancomycin, and ceftazidime for 30 and 56 days in vitro and in vivo, respectively. Histological assays revealed no notable tissue inflammation. Therefore, hybrid biodegradable PLGA nanofibers with a sustainable release of antifungal and antibacterial agents may be employed for the treatment of polymicrobial osteomyelitis.

Cyclodextrins Allow the Combination of Incompatible Vancomycin and Ceftazidime into an Ophthalmic Formulation for the Treatment of Bacterial Keratitis

Ceftazidime (CZ) and vancomycin (VA) are two antibiotics used to treat bacterial keratitis. Due to their physical incompatibility (formation of a precipitate), it is not currently possible to associate both molecules in a single container for ophthalmic administration. We firstly characterized the incompatibility then investigated if 2-hydroxypropyl-beta (HPβCD) and 2-hydroxypropyl-gamma cyclodextrins (HPγCD) could prevent this incompatibility. The impact of pH on the precipitation phenomena was investigated by analysing the supernatant solution of the mixture using high performance liquid chromatography. A characterization of the inclusion of CZ with HPγCD using ¹H nuclear magnetic resonance (NMR), and VA with HPβCD using ¹H-NMR and a solubility diagram was performed. A design of experiment was built to determine the optimal conditions to obtain a formulation that had the lowest turbidity and particle count. Our results showed that VA and CZ form an equimolar precipitate below pH 7.3. The best formulation obtained underwent an in-vitro evaluation of its antibacterial activity. The impact of HPCDs on incompatibility has been demonstrated through the inclusion of antibiotics and especially VA. The formulation has been shown to be able to inhibit the incompatibility for pH higher than 7.3 and to possess unaltered antibacterial activity.

Intravenous Compatibility of Ceftazidime-Avibactam and Aztreonam Using Simulated and Actual Y-site Administration

PURPOSE

The objective of this communication was to determine the intravenous compatibility of ceftazidime/avibactam and aztreonam using simulated and actual Y-site administration.

METHODS

Ceftazidime-avibactam was reconstituted and diluted to concentrations of 8, 25, and 50 mg/mL in 0.9% sodium chloride. Aztreonam was reconstituted and diluted to concentrations of 10 and 20 mg/mL. Each combination of concentrations was tested for compatibility using visual, Tyndall beam, microscopy, turbidity, and pH assessments. Microscopy results were compared to those from sodium chloride 0.9% in water, pH was compared to that at time 0, and turbidity of combinations was compared to that of individual agents. Actual Y-site mixing was conducted over 2-h infusions with samples collected at 0, 1, and 2 h. Test results were evaluated at 0, 1, 2, 4, 8, and 12 h after mixing. All experiments were completed in triplicate.

FINDINGS

Across simulated and actual Y-site experiments, no evidence of incompatibility between combinations of ceftazidime-avibactam + aztreonam was observed. Visual and microscopic tests revealed no particulate matter, color changes, or turbidity. Tyndall beam tests were negative with all combinations. No evidence of incompatibility was observed in turbidity testing. The pH values were consistent across each of the 6 combinations, from immediately after mixing until 12 h after mixing. When the addition of agents was reversed in simulated Y-site experiments, no differences in compatibility were observed. No differences in compatibility between actual and simulated Y-site administration were observed, and there was minimal variability across all replicate experiments.

IMPLICATIONS

Ceftazidime-avibactam, at concentrations of 8, 25, and 50 mg/mL, appeared compatible with aztreonam at concentrations of 10 and 20 mg/mL.

Antagonism between substitutions in β-lactamase explains a path not taken in the evolution of bacterial drug resistance

CTX-M β-lactamases are widespread in Gram-negative bacterial pathogens and provide resistance to the cephalosporin cefotaxime but not to the related antibiotic ceftazidime. Nevertheless, variants have emerged that confer resistance to ceftazidime. Two natural mutations, causing P167S and D240G substitutions in the CTX-M enzyme, result in 10-fold increased hydrolysis of ceftazidime. Although the combination of these mutations would be predicted to increase ceftazidime hydrolysis further, the P167S/D240G combination has not been observed in a naturally occurring CTX-M variant. Here, using recombinantly expressed enzymes, minimum inhibitory concentration measurements, steady-state enzyme kinetics, and X-ray crystallography, we show that the P167S/D240G double mutant enzyme exhibits decreased ceftazidime hydrolysis, lower thermostability, and decreased protein expression levels compared with each of the single mutants, indicating negative epistasis. X-ray structures of mutant enzymes with covalently trapped ceftazidime suggested that a change of an active-site Ω-loop to an open conformation accommodates ceftazidime leading to enhanced catalysis. 10-μs molecular dynamics simulations further correlated Ω-loop opening with catalytic activity. We observed that the WT and P167S/D240G variant with acylated ceftazidime both favor a closed conformation not conducive for catalysis. In contrast, the single substitutions dramatically increased the probability of open conformations. We conclude that the antagonism is due to restricting the conformation of the Ω-loop. These results reveal the importance of conformational heterogeneity of active-site loops in controlling catalytic activity and directing evolutionary trajectories.

Magnetic zeolite imidazole framework material-8 as an effective and recyclable adsorbent for removal of ceftazidime from aqueous solution

Zeolitic imidazolate framework-8 (ZIF-8) was synthesized by solvothermal method and the adsorption pore size was adjusted by changing the amount of template agent. The ZIF-8@SiO₂@Fe₃O₄ derived from self-assembly of ZIF-8 and SiO₂@Fe₃O₄ were then synthesized and used for ceftazidime (CAZ) removal. ZIF-8 was a regular dodecahedral particle with uniform particle size. The pore diameter was 6.47 nm and the specific surface area was 1182.5 m²·g^-1 in ZIF-8@SiO₂@Fe₃O₄. The adsorption of CAZ on ZIF-8@SiO₂@Fe₃O₄ as a function of adsorption temperature, contact time, ionic strength solution pH, and humic acid concentration were investigated. The error of equilibrium adsorption capacity between model fitting and actual experiments is only 1.19%. Kinetics for CAZ removal on ZIF-8@SiO₂@Fe₃O₄ was found to follow pseudo-second-order kinetics. Langmuir, Freundlich and Sips isotherm fitted the adsorption data well and gave similar correlation coefficients, suggesting a single layer adsorption of CAZ on ZIF-8@SiO₂@Fe₃O₄. The ZIF-8@SiO₂@Fe₃O₄ showed no apparent loss in CAZ adsorption after five cycles. These features indicate that the ZIF-8@SiO₂@Fe₃O₄ may be a promising adsorbent for CAZ removal from aqueous solution.

Molecular Basis of Class A β-Lactamase Inhibition by Relebactam

β-Lactamase production is the major β-lactam resistance mechanism in Gram-negative bacteria. β-Lactamase inhibitors (BLIs) efficacious against serine β-lactamase (SBL) producers, especially strains carrying the widely disseminated class A enzymes, are required. Relebactam, a diazabicyclooctane (DBO) BLI, is in phase 3 clinical trials in combination with imipenem for the treatment of infections by multidrug-resistant Enterobacteriaceae We show that relebactam inhibits five clinically important class A SBLs (despite their differing spectra of activity), representing both chromosomal and plasmid-borne enzymes, i.e., the extended-spectrum β-lactamases L2 (inhibition constant 3 μM) and CTX-M-15 (21 μM) and the carbapenemases KPC-2, -3, and -4 (1 to 5 μM). Against purified class A SBLs, relebactam is an inferior inhibitor compared with the clinically approved DBO avibactam (9- to 120-fold differences in half maximal inhibitory concentration [IC₅₀]). MIC assays indicate relebactam potentiates β-lactam (imipenem) activity against KPC-producing Klebsiella pneumoniae, with similar potency to avibactam (with ceftazidime). Relebactam is less effective than avibactam in combination with aztreonam against Stenotrophomonas maltophilia K279a. X-ray crystal structures of relebactam bound to CTX-M-15, L2, KPC-2, KPC-3, and KPC-4 reveal its C2-linked piperidine ring can sterically clash with Asn104 (CTX-M-15) or His/Trp105 (L2 and KPCs), rationalizing its poorer inhibition activity than that of avibactam, which has a smaller C2 carboxyamide group. Mass spectrometry and crystallographic data show slow, pH-dependent relebactam desulfation by KPC-2, -3, and -4. This comprehensive comparison of relebactam binding across five clinically important class A SBLs will inform the design of future DBOs, with the aim of improving clinical efficacy of BLI-β-lactam combinations.

Antibacterial Countermeasures via Metal-Organic Framework-Supported Sustained Therapeutic Release

Long-term antimicrobial therapies are necessary to treat infections caused by virulent intracellular pathogens, including biothreat agents. Current treatment plans include injectable therapeutics given multiple times daily over a period for up to 8 weeks. Here, we present a metal-organic framework (MOF), zeolitic imidazolate framework-8 (ZIF-8), as a robust platform to support the sustained release of ceftazidime, an important antimicrobial agent for many critical bacterial infections. Detailed material characterization confirms the successful encapsulation of ceftazidime within the ZIF-8 matrix, indicating sustained drug release for up to a week. The antibacterial properties of ceftazidime@ZIF-8 particles were confirmed against Escherichia coli, chosen here as a representative of Gram-negative bacteria infection model in a proof-of-concept study. Further, we showed that this material system is compatible with macrophage and lung epithelial cell lines, relevant targets for antibacterial therapy for pulmonary and intracellular infections. A promising methodology to enhance the treatment of intracellular infections is to deliver the antibiotic cargo intracellularly. Importantly, this is the first study to unequivocally demonstrate direct MOF particle internalization using confocal microscopy via 3D reconstructions of z-stacks, taking advantage of the intrinsic emission properties of ZIF-8. This is an important development as it circumvents the need to use any staining dyes and addresses current methodology limitations concerning false impression of cargo uptake in the event of the carrier particle breakdown within biological media.

Coordination and redox interactions of β-lactam antibiotics with Cu2+ in physiological settings and the impact on antibacterial activity

An increase in the copper pool in body fluids has been related to a number of pathological conditions, including infections. Copper ions may affect antibiotics via the formation of coordination bonds and/or redox reactions. Herein, we analyzed the interactions of Cu²⁺ with eight β-lactam antibiotics using UV-Vis spectrophotometry, EPR spectroscopy, and electrochemical methods. Penicillin G did not show any detectable interactions with Cu²⁺. Ampicillin, amoxicillin and cephalexin formed stable colored complexes with octahedral coordination environment of Cu²⁺ with tetragonal distortion, and primary amine group as the site of coordinate bond formation. These β-lactams increased the solubility of Cu²⁺ in the phosphate buffer. Ceftazidime and Cu²⁺ formed a complex with a similar geometry and gave rise to an organic radical. Ceftriaxone-Cu²⁺ complex appears to exhibit different geometry. All complexes showed 1:1 stoichiometry. Cefaclor reduced Cu²⁺ to Cu¹⁺ that further reacted with molecular oxygen to produce hydrogen peroxide. Finally, meropenem underwent degradation in the presence of copper. The analysis of activity against Escherichia coli and Staphylococcus aureus showed that the effects of meropenem, amoxicillin, ampicillin, and ceftriaxone were significantly hindered in the presence of copper ions. The interactions with copper ions should be taken into account regarding the problem of antibiotic resistance and in the selection of the most efficient antimicrobial therapy for patients with altered copper homeostasis.

Synthesis, spectroscopic, biological activity and thermal characterization of ceftazidime with transition metals

Synthesis, physicochemical characterization and thermal analysis of ceftazidime complexes with transition metals (Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II)) were discussed. It's obtained that ceftazidime act as bidentate ligand. From magnetic measurement and spectral data, octahedral structures were proposed for all complexes except for cobalt, nickel and mercury had tetrahedral structural. Hyper chemistry program confirmed binding sites of ceftazidime. Ceftazidime complexes show higher activity than ceftazidime for some strains. From TG and DTA curves the thermal decomposition mechanisms of ceftazidime and their metal complexes were suggested. The thermal decomposition of the complexes ended with the formation of metal oxides as a final product except in case of Hg complex.

The interactions of cephalosporins on polyol pathway enzymes from sheep kidney

CONTEXT

Cephalosporins are derived from the fungus Acremonium. Due to their strong bactericidal ability, these drugs have to a wide usage in medicine.

OBJECTIVE

An investigation of the effects on sheep renal aldose reductase (AR) and sorbitol dehydrogenase (SDH) of cefoperazone, cefazolin, cefuroxime, ceftazidime and ceftriaxone as cephalosporin drugs was carried out in the present study.

METHODS

AR and SDH were purified from sheep kidney by ion exchange, gel filtration and affinity methods with approximately 219- and 484-fold, respectively. Some kinetic properties of the enzymes were determined such as optimal pH, optimal ionic strength, optimal temperature, stable pH, K_m and V_max. IC₅₀ values of the drugs were found for each enzyme.

RESULTS

While the AR was inhibited by all drugs, SDH enzyme was inhibited by only CXM (IC₅₀ 8.10 mM). Interestingly, CZO activated SDH enzyme. This result was evaluated as important for the flow of the polyol reactions. K_i values and inhibition types were determined for AR. However, these values could not have determined for SDH, due to insufficient inhibition.

CONCLUSIONS

From these results, it was concluded that cephalosporins may have an important effect on flow of the polyol metabolism.

Investigation of the removal mechanism of antibiotic ceftazidime by green algae and subsequent microbic impact assessment

The present study provides an integrated view of algal removal of the antibiotic ceftazidime and its basic parent structure 7-aminocephalosporanic acid (7-ACA), including contribution analysis, bacteriostatic and aquatic toxic assessment and metabolite verification. 92.70% and 96.07% of the two target compounds was removed after the algal treatment, respectively. The algal removal can be separated into three steps: a rapid adsorption, a slow cell wall-transmission and the final biodegradation. Additionally, while ceftazidime demonstrated an excellent inhibitory effect on Escherichia coli, there was no bacteriostasis introduced after the algal treatment, which could avoid favoring the harmful selective pressure. On the other hand, no significant aquatic impact of the two target compounds on rotifers was observed and it was not enhanced after the algal treatment. To better reveal the mechanism involved, metabolite analyses were performed. Δ-3 ceftazidime and trans-ceftazidime were regarded as the metabolites of ceftazidime and the metabolite of 7-ACA was regarded as a compound which shared the similar structure with 4-chlorocinnamic acid. Our study indicated that the green algae performed a satisfactory growth capacity and played a dominant role for the biodegradation of the target antibiotics, which achieved high removal efficiency and low environmental impact.

Microspectrofluorimetry to dissect the permeation of ceftazidime in Gram-negative bacteria

A main challenge in chemotherapy is to determine the in cellulo parameters modulating the drug concentration required for therapeutic action. It is absolutely urgent to understand membrane permeation and intracellular concentration of antibiotics in clinical isolates: passing the membrane barrier to reach the threshold concentration inside the bacterial periplasm or cytoplasm is the pivotal step of antibacterial activity. Ceftazidime (CAZ) is a key molecule of the combination therapy for treating resistant bacteria. We designed and synthesized different fluorescent CAZ derivatives (CAZ*, CAZ**) to dissect the early step of translocation-accumulation across bacterial membrane. Their activities were determined on E. coli strains and on selected clinical isolates overexpressing ß-lactamases. The accumulation of CAZ* and CAZ** were determined by microspectrofluorimetry and epifluorimetry. The derivatives were properly translocated to the periplasmic space when we permeabilize the outer membrane barrier. The periplasmic location of CAZ** was related to a significant antibacterial activity and with the outer membrane permeability. This study demonstrated the correlation between periplasmic accumulation and antibiotic activity. We also validated the method for approaching ß-lactam permeation relative to membrane permeability and paved the way for an original matrix for determining "Structure Intracellular Accumulation Activity Relationship" for the development of new therapeutic candidates.

Biodegradable drug-eluting nanofiber-enveloped implants for sustained release of high bactericidal concentrations of vancomycin and ceftazidime: in vitro and in vivo studies

We developed biodegradable drug-eluting nanofiber-enveloped implants that provided sustained release of vancomycin and ceftazidime. To prepare the biodegradable nanofibrous membranes, poly(D,L)-lactide-co-glycolide and the antibiotics were first dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol. They were electrospun into biodegradable drug-eluting membranes, which were then enveloped on the surface of stainless plates. An elution method and a high-performance liquid chromatography assay were employed to characterize the in vivo and in vitro release rates of the antibiotics from the nanofiber-enveloped plates. The results showed that the biodegradable nanofiber-enveloped plates released high concentrations of vancomycin and ceftazidime (well above the minimum inhibitory concentration) for more than 3 and 8 weeks in vitro and in vivo, respectively. A bacterial inhibition test was carried out to determine the relative activity of the released antibiotics. The bioactivity ranged from 25% to 100%. In addition, the serum creatinine level remained within the normal range, suggesting that the high vancomycin concentration did not affect renal function. By adopting the electrospinning technique, we will be able to manufacture biodegradable drug-eluting implants for the long-term drug delivery of different antibiotics.

[Study on electrochemical degradation of ceftazidime by carbon nanotubes electrode]

A self-made multi-walled carbon nanotubes electrode was characterized by SEM, FITR, CV and Tafel, and applied to study the electrochemical reduction degradation of refractory organics, using ceftazidime as model pollutant, and the mass concentration after the reduction was measured by the HPLC. The results indicate that the electrode has perfect stability, good resistance to corrosion, and perfect performance. According to the CV, a larger oxidation peak was obtained at about 800 mV, with a peak value of -0.2 mA, and the degradation of ceftazidime on the electrode was irreversible. The optimum conditions of the the electrochemical reduction degradation of ceftazidime on carbon nanotubes electrode were: electrode spacing of 1 cm, a voltage of 15 V, an initial concentration of 1 mg x L(-1), ionic strength of 1 g x L(-1), and a pH value of 6.0. Under such conditions, the removal efficiency of ceftazidime reached up to 90% when the reaction time was 60 min, and the degradation process conforms to the second-order kinetics.

New insights in the production of aerosol antibiotics. Evaluation of the optimal aerosol production system for ampicillin-sulbactam, meropenem, ceftazidime, cefepime and piperacillin-tazobactam

BACKGROUND

Several aerosol antibiotics are on the market and several others are currently being evaluated. Aim of the study was to evaluate the aerosol droplet size of five different antibiotics for future evaluation as an aerosol administration.

MATERIALS AND METHODS

The nebulizers Sunmist(®), Maxineb(®) and Invacare(®) were used in combination with four different "small <6 ml" residual cups and two "large <10 ml" with different loadings 2-4-6-8 ml (8 ml only for large residual cups) with five different antibiotic drugs (ampicilln-sulbactam, meropenem, ceftazidime, cefepime and piperacillin-tazobactam). The Mastersizer 2000 (Malvern) was used to evaluate the produced droplet size from each combination

RESULTS

Significant effect on the droplet size produced the different antibiotic (F=96.657, p<0.001) and the residual cup design (F=68.535, p<0.001) but not the different loading amount (p=0.127) and the nebulizer (p=0.715). Interactions effects were found significant only between antibiotic and residual cup (F=16.736, p<0.001). No second order interactions were found statistically significant.

CONCLUSION

Our results firstly indicate us indirectly that the chemical formulation of the drug is the main factor affecting the produced droplet size and secondly but closely the residual cup design.

Stability of ceftazidime in 1% and 5% buffered eye drops determined with HPLC method

The aim of the studies was to determine with HPLC method the stability of ceftazidime in buffered 1% and 5% eye drops of proposed formulary composition, which were stored for 30 days at the temperature of 4 degrees C and 20 degrees C and protected from light. The 1% and 5% eye drops were prepared under aseptic conditions by dissolving Biotum (ceftazidimum), dry injection formulation, in citrate buffer of pH 6.10-6.24. The viscosity of the eye drops was increased with polyvinyl alcohol, phenylmercuric borate combined with 2-phenylethanol was used to preserve the eye drops. The eye drops were stored for 30 days in sterile glass bottles at the temperature of 4 degrees C and 20 degrees C and protected from light. The concentration of ceftazidime and pyridine was analyzed simultaneously with HPLC method every three days; pH, osmotic pressure and viscosity were examined as well as the organoleptic analysis of the eye drops (clarity, color, odor). Storage temperature had the biggest impact on ceftazidime stability in the eye drops. The stability of the drops depended also on ceftazidime concentration in the eye drops, the presence of preservatives and polyvinyl alcohol. The time of 10% ceftazidime degradation in buffered 1% and 5% eye drops, stored at the temperature of 4 degrees C, was from 27 to 18 days in 1% eye drops and from 21 to 12 days in 5% eye drops, depending on their composition. In the eye drops which were stored at the temperature of 20 degrees C 10% ceftazidime degradation occurred on the 3rd day of storage in all 1% and 5% formulary versions.

Technology of eye drops containing metronidazole

The aim of the studies was to determine the stability of metronidazole using UV spectrophotometric method in 0.5% w/w eye drops which were prepared under aseptic conditions and thermally sterilized. 0.9% solution of NaCl, 5% glucose and phosphate buffers of pH 6.97 and 6.81 were used as the solvents of metronidazole in the drops. Thiomersal and phenylmercuric borate were used to preserve the drops. The viscosity of the eye drops was increased using the solution of polyvinyl alcohol. The drops were stored in tightly closed glass infusion bottles, protected from light. For the stability of analysis a long-term assay was used under controlled conditions following the requirements of ICH, i.e., the time of storage was 24 months at the constant temperature of 25 +/- 2 degrees C and constant humidity of 60% +/- 2% RH. The eye drops containing metronidazole were significantly physically and chemically stable: after 24 months of storage the metronidazole concentration in the drops was close to 100% of the initial concentration. The drops were colorless and transparent. Physical and chemical properties such as pH, osmotic pressure and viscosity underwent insignificant changes during the storage. The preservation test showed that the degree of reduction of the pharmacopeal strains of micro-organisms in freshly prepared drops and in those stored for 24 months at the temperature of 25 +/- 20 degrees C was in agreement with the requirements of Ph. Eur. 6.

Crystal structures of penicillin-binding protein 3 from Pseudomonas aeruginosa: comparison of native and antibiotic-bound forms

We report the first crystal structures of a penicillin-binding protein (PBP), PBP3, from Pseudomonas aeruginosa in native form and covalently linked to two important β-lactam antibiotics, carbenicillin and ceftazidime. Overall, the structures of apo and acyl complexes are very similar; however, variations in the orientation of the amino-terminal membrane-proximal domain relative to that of the carboxy-terminal transpeptidase domain indicate interdomain flexibility. Binding of either carbenicillin or ceftazidime to purified PBP3 increases the thermostability of the enzyme significantly and is associated with local conformational changes, which lead to a narrowing of the substrate-binding cleft. The orientations of the two β-lactams in the active site and the key interactions formed between the ligands and PBP3 are similar despite differences in the two drugs, indicating a degree of flexibility in the binding site. The conserved binding mode of β-lactam-based inhibitors appears to extend to other PBPs, as suggested by a comparison of the PBP3/ceftazidime complex and the Escherichia coli PBP1b/ceftoxamine complex. Since P. aeruginosa is an important human pathogen, the structural data reveal the mode of action of the frontline antibiotic ceftazidime at the molecular level. Improved drugs to combat infections by P. aeruginosa and related Gram-negative bacteria are sought and our study provides templates to assist that process and allows us to discuss new ways of inhibiting PBPs.

[Spectrophotometric and HPLC evaluation of ceftazidime stability]

In this paper we followed up the stability of ceftazidime, raw material used in drug industry. Matherials and methods: We used three spectrophotometric methods based on ceftazidime property to form complexes with p-chloranilic acid (ac. p-CA), 3-methylbenzothiazolin-2-on hydrazone (MBTH) and N-(1-naphtil) etilendiamine (NEDA) and a chromatographic method (HPLC).

RESULTS

Our results revealed that the substances analyzed maintained minimum content allowable.

Stability and antibacterial potency of ceftazidime and vancomycin eyedrops reconstituted in BSS against Pseudomonas aeruginosa and Staphylococcus aureus

PURPOSE

We aimed to study the stability and the in vitro antibacterial potency of ceftazidime and vancomycin eyedrops against Pseudomonas aeruginosa and Staphylococcus aureus, respectively, under different storage temperatures and light conditions.

METHODS

Solutions of ceftazidime 50 mg/ml and vancomycin 50 mg/ml were prepared by reconstituting with balanced salt solution (BSS) and stored at 4 degrees C and at 24 degrees C with and without exposure to light. The minimum bactericidal concentrations against P. aeruginosa and S. aureus were measured to evaluate the antimicrobial potency over a 4-week period. Changes in the pH values and physical characteristics of the solutions were recorded over the same period of time.

RESULTS

The antibacterial potency of ceftazidime decreased significantly from days 3 and 7 onwards at storage temperatures of 24 degrees C and 4 degrees C, respectively, but was not affected by light exposure. The pH value progressed from acidic to alkaline, peaking at day 3, in all solutions. The antibacterial potency of vancomycin remained stable during the 4-week period, but its pH showed a slight progression from acidic to less acidic, in all solutions.

CONCLUSIONS

Ceftazidime eyedrops in BSS appear to remain effective against P. aeruginosa for > or = 7 days when stored at 4 degrees C, but were less effective when stored at 24 degrees C. Loss of antibacterial potency coincides with the appearance of visual and olfactory signs of degradation. The transient rise in pH at day 3 is a matter of possible concern, however, as it may affect patient tolerance. By contrast, vancomycin eyedrops in BSS can be safely used for > or = 4 weeks, stored at either 4 degrees C or 24 degrees C.

[Determination of ceftazidime and impurities using high performance liquid chromatography]

A high performance liquid chromatographic (HPLC) method for the determination of ceftazidime and impurities in ceftazidime drug was developed and verified. An Alltima C18 column (250 mm x 4.6 mm, 5 microm) was used as the analysis column. Acetonitrile and phosphate buffer (22.6 g/L aqueous solution of ammonium dihydrogen phosphate, adjusted to pH 3.9 with 10% (v/v) phosphoric acid) were used as mobile phases with gradient elution at a flow rate of 1.3 mL/min. The column temperature was kept at 35 degrees C, and the detection wavelength was set at 255 nm. Fourteen impurities could be well separated. The assay exhibited a good linearity in the ceftazidime concentration range of 0.267-1069 microg/mL with a correlation coefficient of 1.0000. The limits of the quantitation and qualification of ceftazidime were 3.1 ng and 0.93 ng, respectively. The relative standard deviations (RSDs) of the interday and intraday (n=3) determinations at three concentration levels were 0.72% and 0.91%, respectively. At 4 degrees C ang under darkness, ceftazidime solution was stable for 24 h. The developed method is superior to the counterparts in British and Japanese pharmacopeias in the number of the impurities separated and detected.

Study on the resonance Rayleigh scattering spectra of the interactions of palladium (II)–cephalosporins chelates with 4,5-dibromofluorescein and their analytical applications

In pH 2.8-3.8 BR buffer medium, the third generation cephalosporin antibiotics (TGCs) such as ceftazidime (CZD), ceftriaxone (CTRX), cefoperazone (CPZ), and cefotaxime (CFTM) react with palladium(II) (Pd(II)) to form 1:2 yellowish-brown cationic chelates, which further react with 4,5-dibromofluorescein (DBF) to form 1:3 brown ion-association complexes. As a result, not only the spectra of absorption and fluorescence are changed, but also the resonance Rayleigh scattering (RRS) is enhanced greatly and the new RRS spectra are observed. The four TGCs products have similar spectral characteristics and their maximum RRS wavelengths are all located at 291 nm. The quantitative determination ranges and the detection limits of the four TGCs are 0.0065-1.0 microg mL(-1) and 2.0 ng mL(-1) for CZD, 0.0070-1.1 microg mL(-1) and 2.2 ng mL(-1) for CTRX, 0.0090-1.6 microg mL(-1) and 2.7 ng mL(-1) for CPZ, and 0.014-2.2 microg mL(-1) and 4.2 ng mL(-1) for CFTM, respectively. The optimum conditions of the reactions and the effects of foreign substances are investigated, and the composition of ion-association complexes is discussed also. Based on the ion-association reaction, a highly sensitive, simple and rapid method has been proposed to the determination of TGCs.

Investigating protein structural plasticity by surveying the consequence of an amino acid deletion from TEM-1 beta-lactamase

While the deletion of an amino acid is a common mutation observed in nature, it is generally thought to be disruptive to protein structure. Using a directed evolution approach, we find that the enzyme TEM-1 beta-lactamase was broadly tolerant to the deletion mutations sampled. Circa 73% of the variants analysed retained activity towards ampicillin, with deletion mutations observed in helices and strands as well as regions important for structure and function. Several deletion variants had enhanced activity towards ceftazidime compared to the wild-type TEM-1 demonstrating that removal of an amino acid can have a beneficial outcome.

Influence of additives and storage temperature on physicochemical and microbiological properties of eye drops containing ceftazidime

The purpose of the studies was to examine the influence of additives and the storage temperature on the physicochemical properties of the eye drops containing ceftazidime and on the antimicrobial activity of ceftazidime in the eye drops stored for 30 days at the temperature of 4 degrees C and 2 degrees C. The eye drops were 1% sterile aqueous solutions of Biotum (Ceftazidimum) in citrate buffer of pH 6.18-6.30, which were preserved with 0.002% thiomersal or 0.001% phenylmercuric borate mixed with 0.4% beta-phenylethyl alcohol. The viscosity of the eye drops was increased with polyvinyl alcohol. The pharmaceutical compatibility test showed the pharmaceutical interaction of 1% solution of Biotum with thiomersal at the concentration higher than 0.003%, with 0.01% chlorhexidine diacetate and with 15% polyvinylpyrrolidone. As the criteria of the qualitative assessment of both freshly prepared eye drops and those stored at the temperature of 4 degrees C and 20 degrees C, the following analyses were considered: organoleptic analysis (color, clarity, and smell), sterility, pH, osmotic pressure and viscosity. The antimicrobial activity of ceftazidime and the preservation efficiency of thiomersal and phenylmercuric borate in the eye drops were determined using methods of the Polish Pharmacopoeia VI (PPh VI). The antimicrobial activity of ceftazidime in the drops was especially influenced by their storage temperature. After 30 days of storage at the temperature of 4 degrees C, there was no decrease of antimicrobial activity of ceftazidime detected in the eye drops. However, when the eye drops were stored at the temperature of 20 degrees C, the decrease of antimicrobial activity of ceftazidime was observed already after 14 days. After 30 days of storage both at the temperature of 4 degrees C and 20 degrees C, neither pH nor viscosity of the eye drops changed; however, the osmotic pressure was decreased.

Relationship between lipophilicity of BCS class III and IV drugs and the functional activity of peroral absorption enhancers

Absorption enhancers (AEs) have been shown to be specific in permeation enhancement capabilities because of which they increase absorption of some drug molecules more than others. Present study was designed to investigate the relationship between lipophilicity of drug molecules and the absorption enhancement potential of AEs. Four drug molecules of different lipophilicity were selected as model compounds, namely, cefotaxime sodium, ceftazidime pentahydrate, lovastatin and cyclosporin A. Their apparent permeability coefficients in the absence and presence of three classes of AEs (fatty acids, cyclodextrins, and bile salts) were determined using in vitro everted rat intestinal sac absorption model. Significant relationship was observed between log P of drug and absorption enhancement ratios by AEs. This relationship was found to be functionally directly or indirectly proportional depending upon nature of AE and explain the mechanism of permeation enhancement.

Examination of stability and compatibility of flucloxacillin (Floxapen®) and ceftazidime (Fortum®) in two infusion media: relevance for the clinical praxis

Flucloxacillin (Floxapen) and ceftazidime (Ceftazidim) are both highly active antibiotics against Gram-positive and Gram-negative organisms, respectively. Because of their complementary spectra of activity, simultaneous administration of both drugs via continuous infusion is highly favored by clinicians. Therefore, the aim of the present study was to examine the stability and compatibility of both drugs in Aqua ad injections and in physiological solution of sodium chloride in the presence and absence of furosemide (Lasix). Physical and chemical stability were examined using different concentrations of flucloxacillin (2-12 g/50 ml) and ceftazidime (2-9 g/50 ml). On the basis of a limit of max. 10% degradation, flucloxacillin and ceftazidime can be considered stable at 4 degrees C and room temperature for up to 24 hours. Neither concentration nor infusion medium had significant influence on the degradation of both compounds. Addition of furosemide (250 mg/50 ml) does not cause any incompatibilities or significant decrease of the antimicrobial drug concentrations.

Long-Circulating Sterically Stabilized Liposomes in the Treatment of Infections

The administration of antimicrobial agents encapsulated in long-circulating sterically stabilized liposomes results in a considerable enhancement of therapeutic efficacy compared with the agents in the free form. After liposomal encapsulation, the pharmacokinetics of the antimicrobial agents is significantly changed. An increase in circulation time and reduction in toxic side effects of the agents are observed. In contrast to other types of long-circulating liposomes, an important characteristic of these sterically stabilized liposomes is that their prolonged blood circulation time is, to a high degree, independent of liposome characteristics such as liposome particle size, charge and lipid composition (rigidity) of the bilayer, and lipid dose. This provides the opportunity to manipulate antibiotic release from these liposomes at the site of infection, which is important in view of the differences in pharmacodynamics of different antibiotics and can be done without compromising blood circulation time and degree of target localization of these liposomes. Depending on the liposome characteristics and the agent encapsulated, antibiotic delivery to the infected site is achieved, or the liposomes act as a micro-reservoir function for the antibiotic. In experimental models of localized or disseminated bacterial and fungal infections, the sterically stabilized liposomes have successfully been used to improve antibiotic treatment using representative agents of various classes of antibacterial agents such as the beta-lactams, the aminoglycosides, and the quinolones or the antifungal agent amphotericin B. Extensive biodistribution studies have been performed. Critical factors that contribute to liposome target localization in infected tissue have been elucidated. Liposome-related factors that were investigated were poly(ethylene glycol) density, particle size, bilayer fluidity, negative surface charge, and circulation kinetics. Host-related factors focused on the components of the inflammatory response.

X-ray Crystal Structure of the Acylated β-Lactam Sensor Domain of BlaR1 from Staphylococcus aureus and the Mechanism of Receptor Activation for Signal Transduction

Methicillin-resistant strains of Staphylococcus aureus (MRSA) are the major cause of infections worldwide. Transcription of the beta-lactamase and PBP2a resistance genes is mediated by two closely related signal-transducing integral membrane proteins, BlaR1 and MecR1, upon binding of the beta-lactam inducer to the sensor domain. Herein we report the crystal structure at 1.75 A resolution of the sensor domain of BlaR1 in complex with a cephalosporin antibiotic. Activation of the signal transducer involves acylation of serine 389 by the beta-lactam antibiotic, a process promoted by the N-carboxylated side chain of Lys392. We present evidence that, on acylation, the lysine side chain experiences a spontaneous decarboxylation that entraps the sensor in its activated state. Kinetic determinations and quantum mechanical/molecular mechanical calculations and the interaction networks in the crystal structure shed light on how this unprecedented process for activation of a receptor may be achieved and provide insights into the mechanistic features that differentiate the signal-transducing receptor from the structurally related class D beta-lactamases, enzymes of antibiotic resistance.

Unexpected advanced generation cephalosporinase activity of the M69F variant of SHV beta-lactamase

Infections with bacteria that contain hydrolytic beta-lactamase enzymes are becoming a serious problem in the United States. Mutations at Met-69, an amino acid proximal to the active site Ser-70 in the TEM-1 and SHV-1 beta-lactamases, have emerged as a puzzling cause of bacterial resistance to inhibitors of beta-lactamases. Site-saturation mutagenesis of the 69 position in SHV beta-lactamase was performed to determine how mutations of this non-catalytic residue play a role in increasing 50% inhibitory concentrations (IC(50) concentrations) for clinically important beta-lactamase enzyme inhibitors. Two distinct phenotypes are evident in the variant beta-lactamases studied: significantly increased minimum inhibitory concentrations (microg/ml) and IC(50) concentrations to clavulanic acid for the Met69Ile, Leu, and Val substitutions, and unanticipated increased minimum inhibitory concentrations and hydrolytic activity toward ceftazidime, an advanced generation cephalosporin antibiotic, for the Met69Lys, Tyr- and Phe-substituted enzymes. Molecular modeling studies emphasize the conserved structure of these substitutions despite great variation in substrate specificity. This study demonstrates the key role of Met-69 in defining substrate specificity of SHV beta-lactamases and alerts us to new phenotypes that may emerge clinically.

Biochemical analysis of the ceftazidime-hydrolysing extended-spectrum beta-lactamase CTX-M-15 and of its structurally related beta-lactamase CTX-M-3

The extended-spectrum beta-lactamase CTX-M-15 confers resistance to ceftazidime, unlike the majority of CTX-M-type enzymes. Kinetic parameters were determined from purified CTX-M-15 and CTX-M-3, which differ by the single amino acid substitution Asp-240 to Gly, according to the Ambler numbering of class A beta-lactamases. Relative molecular masses of CTX-M-15 and CTX-M-3 were approximately 29 kDa and pI values were 8.9 and 8.4, respectively. CTX-M-15 had higher affinities for beta-lactams (lower K(m) values) than those of CTX-M-3 but catalytic efficiency (k(cat)/K(m) values) was variable depending on the beta-lactam substrate. Only CTX-M-15 showed a measurable catalytic efficiency for ceftazidime. Clavulanic acid and tazobactam were good inhibitors of both enzymes. MICs of beta-lactams for Escherichia coli reference strains expressing cloned beta-lactamase genes in the same genetic background were similar except for ceftazidime. This work underlines the fact that some CTX-M enzymes may hydrolyse ceftazidime and thus confer resistance to this expanded-spectrum cephalosporin in Enterobacteriaceae.

Comparative stability studies of antipseudomonal beta-lactams for potential administration through portable elastomeric pumps (home therapy for cystic fibrosis patients) and motor-operated syringes (intensive care units)

The stability of antipseudomonal beta-lactams in concentrated solutions was examined in view of their potential administration by continuous infusion with external pumps (for intensive care patients) or with portable pumps carried under clothing (for cystic fibrosis patients). Aztreonam (100 g/liter), piperacillin (128 g/liter, with tazobactam), and azlocillin (128 g/liter) remained 90% stable for up to more than 24 h at 37 degrees C (mezlocillin [128 g/liter] was stable at 25 degrees C but not at 37 degrees C). Ceftazidime (120 g/liter), cefpirome (32 g/liter), and cefepime (50 g/liter) remained 90% stable for up to 24, 23.7, and 20.5 h at 25 degrees C but only for 8, 7.25, and 13 h at 37 degrees C, respectively. The control of temperature therefore appears to be critical for all three cephalosporins that cannot be recommended for use in portable pumps carried under clothes for prolonged periods for reasons of stability. Cefpirome and cefepime solutions developed an important color change (from light yellow to dark red) upon exposure when stored at 30 degrees C or higher. Degradation of ceftazidime was accompanied by the liberation of pyridine which, at 37 degrees C, was in excess of what is allowed by the U.S. Pharmacopeia, i.e., 1.1 mg/liter, after 8 and 12 h for drug concentrations of 12 and 8.3%, respectively. Imipenem and meropenem are too unstable (10% degradation at 25 degrees C after 3.5 and 5.15 h, respectively) to be recommended for use by continuous infusion. Faropenem, examined in comparison with imipenem and meropenem, proved as stable as aztreonam or piperacillin.

Comparison of ceftazidime degradation in glass bottles and plastic bags under various conditions

OBJECTIVE

To study the effect of type of container on ceftazidime stability in intravenous solutions.

METHODS

One hundred millilitre polypropylene (PP) and polyvinyl chloride (PVC) bags and 100-mL glass bottles were filled with 5% dextrose or 0.9% sodium chloride solutions containing ceftazidime (Fortumset) at 40 mg/mL. Three containers of each solution were stored at 20 and 35 degrees C. One millilitre samples were drawn from each container at 0 and 20 h and assayed. Pyridine concentrations, the main degradation product of ceftazidime, were determined by high-pressure liquid chromatography.

RESULTS

Pyridine levels increased during storage and were higher in PVC and PP bags than in glass bottles in both diluents. Solutions stored in PP bags showed better stability than in PVC bags.

CONCLUSION

This study shows that ceftazidime undergoes slower degradation in PP than PVC containers although the difference is small. Glass bottles seems to be the better container for storing ceftazidime solutions, whatever storage temperature and diluent used.

An in vitro study of ceftazidime and vancomycin concentrations in various fluid media: implications for use in treating endophthalmitis

PURPOSE

To investigate the precipitation process of a mixture of vancomycin and ceftazidime by equilibrium dialysis and determine its subsequent effect on the level of free antibiotics for treatment of endophthalmitis.

METHODS

Concentrations of vancomycin and ceftazidime in an equilibrium dialysis chamber were measured during the equilibrium process by high-performance liquid chromatography. Normal saline (NS), balanced salt solution (BSS), and vitreous were used separately as the medium of dialysis.

RESULTS

Precipitation of ceftazidime occurred at 37 degrees C but not at room temperature and did not affect the pH of the medium. It formed precipitate on its own or when mixed with vancomycin in all the three media of NS, BSS, and vitreous. More precipitation was formed if ceftazidime was initially prepared in BSS than in NS. After 168 hours in the dialysis chambers, ceftazidime prepared in NS precipitated to 54% of that in vitreous, compared with 88% if prepared in BSS. At 48 hours, ceftazidime prepared in NS decreased from an initial concentration of 137.5 to 73.4 microg/mL in vitreous medium and to 6.3 microg/mL if prepared in BSS. Precipitation of vancomycin was negligible.

CONCLUSIONS

Based on this in vitro investigation, ceftazidime precipitates in vitreous at body temperature, regardless of the presence of vancomycin. NS is preferred to BSS as a preparation medium for antibiotics for intravitreal injection, because the extent of ceftazidime precipitation is less. However, due to precipitation, the concentration of free ceftazidime in vitreous may not be sufficiently high for antibacterial activity against most common organisms.

Fortum stability in different disposable infusion devices by pyridine assay

The stability of ceftazidime in 5% dextrose injection and 0.9% sodium chloride injection when stored in a different disposable infusion device was determined. Solutions of ceftazidime 40 mg/ml were used to fill the drug administration devices. Stability was determined for both 5% dextrose injection and 0.9% sodium chloride injection solutions at 37 degrees C in four disposable infusion devices. Ceftazidime and its mean degradation product, pyridine, were simultaneously assayed in triplicate by a stability-indicating high-performance liquid chromatographic (HPLC) method. This method was simple, sensitive (limit of quantitation (LOQ), 2 ng injected for both compounds), rapid (run time was 7 min) and precise (mean recovery was 100.5+/-2.9 and 103.6+/-1.9% for pyridine and ceftazidime, respectively). The ceftazidime stability in the 5% dextrose solution was lower than in the 0.9% sodium chloride solution. When stored at 37 degrees C in a disposable infusion device, the stability of the ceftazidime is included in large hourly range, depending strongly on the manufacturer. The stability of ceftazidime exceed 19 h in none studied cases. The pyridine formed in 24 h was in the range of 100-400 mg depending on devices and infusions.

Structures of ceftazidime and its transition-state analogue in complex with AmpC beta-lactamase: implications for resistance mutations and inhibitor design

Third-generation cephalosporins are widely used beta-lactam antibiotics that resist hydrolysis by beta-lactamases. Recently, mutant beta-lactamases that rapidly inactivate these drugs have emerged. To investigate why third-generation cephalosporins are relatively stable to wild-type class C beta-lactamases and how mutant enzymes might overcome this, the structures of the class C beta-lactamase AmpC in complex with the third-generation cephalosporin ceftazidime and with a transition-state analogue of ceftazidime were determined by X-ray crystallography to 2.0 and 2.3 A resolution, respectively. Comparison of the acyl-enzyme structures of ceftazidime and loracarbef, a beta-lactam substrate, reveals that the conformation of ceftazidime in the active site differs from that of substrates. Comparison of the structures of the acyl-enzyme intermediate and the transition-state analogue suggests that ceftazidime blocks formation of the tetrahedral transition state, explaining why it is an inhibitor of AmpC. Ceftazidime cannot adopt a conformation competent for catalysis due to steric clashes that would occur with conserved residues Val211 and Tyr221. The X-ray crystal structure of the mutant beta-lactamase GC1, which has improved activity against third-generation cephalosporins, suggests that a tandem tripeptide insertion in the Omega loop, which contains Val211, has caused a shift of this residue and also of Tyr221 that would allow ceftazidime and other third-generation cephalosporins to adopt a more catalytically competent conformation. These structural differences may explain the extended spectrum activity of GC1 against this class of cephalosporins. In addition, the complexed structure of the transition-state analogue inhibitor (K(i) 20 nM) with AmpC reveals potential opportunities for further inhibitor design.

Stability of ceftazidime in normal saline solution after exposure to light

Bactericidal activity of ceftazidime is determined by the time that concentrations in tissue and serum are above the MIC for the pathogens during the dosing interval. Thus, the most effective mode of administration of ceftazidime is continuous infusion. However, this agent is light sensitive which may result in instability when administered by this method without protection from light. Until now we have had no data to demonstrate the stability of this drug during continuous infusion. Therefore, the objective of this study was to provide such data. One gram of ceftazidime was mixed with 1,000 ml normal saline and exposed to two 36 watt fluorescence lights for 24 hours. The distance between ceftazidime solution and light source was 1 meter. Twenty samples (1 g-ceftazidime in normal saline) solution were evaluated. The mean ceftazidime concentrations in normal saline solution were decreased by only 1.69%, 4.44% and 7.19% after 6, 12 and 24 hours after exposure to light, respectively. Therefore, we conclude that the reduction of drug concentration was not considered to be significantly high, and this agent can be administered by continuous infusion.

Anti-HIV-1 activity in vitro of ceftazidime degradation products

Cephalosporins in aqueous solutions generate degradation products that inhibit in vitro HIV-1 replication in cell lines, as well as in primary cells (lymphocytes and macrophages). This effect is observed at concentrations that do not interfere with the normal functions of these cells. Upon chromatographic fractionation of an aqueous solution of hydrolysed ceftazidime, a high molecular weight fraction (MW 8000) with antiviral activity was isolated. The exact chemical nature of the active component responsible for the anti-HIV activity in vitro appears to be complex and is currently unknown. Inhibition of HIV-1 reverse transcriptase and RNase H activity was observed, however, higher concentrations than those needed to inhibit HIV replication were required. The inhibitory action of the hydrolysed ceftazidime was manifested during the early phase of the HIV-1 life-cycle. Despite a lack of a direct effect of the CD4/gp120 interaction, HIV-1 mediated cell fusion was inhibited by the hydrolysed ceftazidime, suggesting that the active principle acts in a very early stage of the viral life-cycle.

Compatibility and stability of linezolid injection admixed with three cephalosporin antibiotics

OBJECTIVE

To evaluate the physical compatibility and chemical stability of linezolid (Zyvox-Pharmacia) 200 mg/100 mL admixed with cefazolin sodium 1 gram, ceftazidime 2 grams, and ceftriaxone sodium 1 gram for 7 days at 4 degrees C and 23 degrees C.

DESIGN

Controlled experimental trial.

SETTING

Laboratory.

INTERVENTIONS

The test samples were prepared by adding the required amount of the cephalosporin antibiotic to bags of linezolid injection 200 mg/100 mL.

MAIN OUTCOME MEASURES

Physical stability and chemical stability based on drug concentrations initially and after 1, 3, 5, and 7 days of storage at 4 degrees C and 23 degrees C protected from light.

RESULTS

All of the linezolid admixtures with cephalosporins were clear when viewed in normal fluorescent room light and with a Tyndall beam. Measured turbidity and particulate content were low and exhibited little change. The cefazolin sodium-containing samples were colorless throughout the study. The admixtures with ceftazidime and ceftriaxone sodium had a slight yellow tinge initially, and the room temperature samples became a frank yellow color after 5 days. The refrigerated samples did not change color. High-performance liquid chromatography analysis found little or no loss of linezolid in any sample stored at either temperature throughout the study. Cefazolin sodium and ceftazidime in the linezolid admixtures at 4 degrees C remained stable for 7 days, but at 23 degrees C cefazolin sodium was stable for 3 days and ceftazidime for only 24 hours before cephalosporin decomposition exceeded 10%. Ceftriaxone sodium was less stable in the admixtures; 10% loss occurred in 3 days at 4 degrees C and more than 20% loss occurred in 24 hours at 23 degrees C.

CONCLUSION

Admixtures of linezolid 200 mg/100 mL with cefazolin sodium 1 gram and ceftazidime 2 grams were physically compatible and chemically stable for at least 7 days stored at 4 degrees C protected from light and for 3 days and 1 day, respectively, at 23 degrees C protected from light. Admixtures of linezolid with ceftriaxone sodium 1 gram exhibited a rapid rate of cephalosporin loss at 23 degrees C, which precludes admixture of the two drugs.

Antibiotic-heparin lock: in vitro antibiotic stability combined with heparin in a central venous catheter

Long-term hemodialysis frequently requires vascular access through central venous catheters (CVCs). Infection related to these catheters is a significant complication. The use of an antibiotic-heparin lock could decrease the risks associated with infected permanent catheters. As an initial step in developing an antibiotic-heparin lock, we investigated the in vitro stability of antibiotic-heparin combinations in CVCs. Initially, cefazolin, vancomycin, ceftazidime, ciprofloxacin 10 mg/ml each, and gentamicin 5 mg/ml were incubated separately in glass test tubes in the dark at 37 degrees C for 72 hours. Samples were analyzed spectrophotometrically for stability at 24-hour intervals. The procedure was repeated with the addition of heparin (final concentration 5000 U/ml in glass test tubes), and the combination was also examined in CVCs. High-performance liquid chromatography analysis was conducted on the antibiotic-heparin combinations at 72 hours to confirm the spectrophotometric results. Ciprofloxacin produced an immediate precipitate with the addition of heparin and was not analyzed further. Absorbance values decreased for all antibiotics, with the greatest decreases at 72 hours for cefazolin (27.4%), vancomycin (29.7%), ceftazidime (40.2%), and gentamicin (8%) when combined with heparin. These decreases were postulated to be secondary to adsorption of the antibiotics to the luminal surface of the catheters because submitting the catheters to ultrasound with 1% sodium bicarbonate and analyzing the resulting solution for absorbance revealed that some of the drug was recovered. Although free antibiotic in CVC solution was reduced, the concentration should be sufficient (approximately 5 mg/ml) to decrease the frequency of infections associated with CVCs. We conclude that the concentrations of vancomycin, ceftazidime, cefazolin, or gentamicin used in our study should be sufficient for an antibiotic-heparin lock.

Effects on substrate profile by mutational substitutions at positions 164 and 179 of the class A TEM(pUC19) beta-lactamase from Escherichia coli

We investigated the effects of mutations at positions 164 and 179 of the TEM(pUC19) beta-lactamase on turnover of substrates. The direct consequence of some mutations at these sites is that clinically important expanded-spectrum beta-lactams, such as third-generation cephalosporins, which are normally exceedingly poor substrates for class A beta-lactamases, bind the active site of these mutant enzymes more favorably. We employed site-saturation mutagenesis at both positions 164 and 179 to identify mutant variants of the parental enzyme that conferred resistance to expanded-spectrum beta-lactams by their enhanced ability to turn over these antibiotic substrates. Four of these mutant variants, Arg(164) --> Asn, Arg(164) --> Ser, Asp(179) --> Asn, and Asp(179) --> Gly, were purified and the details of their catalytic properties were examined in a series of biochemical and kinetic experiments. The effects on the kinetic parameters were such that either activity with the expanded-spectrum beta-lactams remained unchanged or, in some cases, the activity was enhanced. The affinity of the enzyme for these poorer substrates (as defined by the dissociation constant, K(s)) invariably increased. Computation of the microscopic rate constants (k(2) and k(3)) for turnover of these poorer substrates indicated either that the rate-limiting step in turnover was the deacylation step (governed by k(3)) or that neither the acylation nor deacylation became the sole rate-limiting step. In a few instances, the rate constants for both the acylation (k(2)) and deacylation (k(3)) of the extended-spectrum beta-lactamase were enhanced. These results were investigated further by molecular modeling experiments, using the crystal structure of the TEM(pUC19) beta-lactamase. Our results indicated that severe steric interactions between the large 7beta functionalities of the expanded-spectrum beta-lactams and the Omega-loop secondary structural element near the active site were at the root of the low affinity by the enzyme for these substrates. These conclusions were consistent with the proposal that the aforementioned mutations would enlarge the active site, and hence improve affinity.

Stability of ceftazidime in a viscous eye drop formulation

OBJECTIVE

To assess the stability of an extemporaneously prepared ceftazidime eye-drop.

METHOD

Ceftazidime was formulated at a concentration of 5% w/v as an eye drop, using Sno Tears, an artificial tear solution containing polyvinyl alcohol, as a vehicle. Two batches of the formulation were stored in 10 ml eye drop bottles at 7 and 25 degrees C for up to 14 days. Ceftazidime and pyridine, its degradation product, were determined at intervals by HPLC.

RESULTS

A yellow coloration was evident after 7 days at 7 degrees C and after 24 h at 25 degrees C. Ceftazidime lost approximately 35% after 7 days storage at 25 degrees C. At 7 degrees C, the mean time to 10% degradation, determined by linear regression, was 11 and 8 days for the two batches. However, the lower 95% confidence limits were 8 and 5 days, respectively. Pyridine levels increased during storage. The mass balance between ceftazidime remaining and pyridine formed was close to 100% during the early part of storage. By the end of storage, the balance had reduced to around 95% at 7 degrees C and 80% at 25 degrees C. This discrepancy may be due to sorption of pyridine to the butyl rubber bottle closure. The pH remained in the range 6-7 throughout the storage period.

CONCLUSION

The formulation may be stored for 5 days in the refrigerator.

Stability of reconstituted solutions of ceftazidime for injections: an HPLC and CE approach

The stability of aqueous reconstituted ceftazidime injection vials containing ceftazidime pentahydrate blended with anhydrous sodium carbonate was investigated in different storage conditions (4 degrees C and 10 degrees C for 7 days in a refrigerator, 20 and 30 degrees C for 24 h) with validated HPLC and (micellar) CE methods. Stability indicating data were obtained for ceftazidime and two degradation products: pyridine and the delta2-ceftazidime isomer. Other degradation products were also identified (the complementarity of the two used experimental procedures was useful in such exercise) and characterized by their UV spectra and retention times. Stability data (7 days at 4 degrees C in a refrigerator and 18 h at room temperature) resulted in agreements with the manufacturers prescription and point out the need of a strict temperature control of the refrigerator's compartment used to store the reconstituted solution.

The mechanism of ceftazidime degradation in aqueous solutions

Degradation of ceftazidime in aqueous solutions was studied at 298 K in acidic, basic and neutral conditions. The subsequent stage of hydrolysis involved the hydrolysis of the group at C-3, opening of the beta-lactam ring, and epimerization at C-6 or C-7. The decomposition of ceftazidime and the formation and identification of product C (pyridine) was followed by HPLC.

Extended-spectrum beta-lactamases and other enzymes providing resistance to oxyimino-beta-lactams

Bacteria have once again demonstrated their remarkably versatility in meeting the introduction of new classes of beta-lactam antibiotics by modifying available plasmid mediated beta-lactamases to expand their spectrum of action and by incorporating chromosomal beta-lactamase genes onto plasmids that permit their spread to new hosts. Such resistance is more common than presently is appreciated because current NCCLS breakpoints for resistance underestimate its prevalence. A number of risk factors for acquisition of ESBL-producing K. pneumoniae have been defined, but most will be no easier to control than those for infection by MRSA or VRE. More clinical and animal model studies are needed to evaluate options for treatment. Most strains remain susceptible to imipenem and other carbapenems, but carbapenem resistance has appeared either by spread of metallo-beta-lactamase or by production of an AmpC enzyme combined with loss of an outer membrane porin channel. Attack on our adversaries' latest biological weapons is likely to require enhanced versatility on our part as well.