Imipenem-metal complexes: Computational analysis and toxicity studies with wastewater model microorganisms.

The occurrence of antibiotic residues in diverse water sources has long been acknowledged as a potential health concern due to the emergence and spread of antibiotic-resistant bacteria and genes. However, there have been limited studies into the presence of antibiotic-metal complexes (AMCs) in real-time wastewater matrices, and their impact on wastewater microbial communities. The present work, in this regard, investigated the stability of Imipenem-metal complexes (Me = Mg (II), Ca (II), Fe (II), Cu (II), and Al (III)) with computational studies, stoichiometry with potentiometric measurements, and their antibacterial activity towards wastewater model microorganisms- Bacillus subtilis (B. subtilis) and Escherichia coli (E. Coli) by Colony Forming Unit (CFU) method. The lower energy of Imipenem-metal complexes than the parent antibiotic- Imipenem, during energy optimization using density functional (DFT) methods, revealed that metal interactions of Imipenem stabilize the drug by minimizing its energy. Further, CFU studies indicated that these complexes display higher antimicrobial activity than parent antibiotics. The electron delocalization over the entire chelated system (AMCs) reduces polarity and increases the lipophilicity of the complexes, thereby facilitating stronger interaction between AMCs and the bacterial cell membrane. Results indicate increased antibacterial activity of Imipenem-metal complexes for both E. coli and B. subtilis. The antibacterial activity, was however, more pronounced in B. subtilis, with >97% growth inhibition for metal complexes of Imipenem (at a Minimum Inhibitory Concentration of 20 nM or 6 ppb (i.e., MIC90)), for both the stoichiometric ratios (metal to ligand) ratios (M: L 1: 1 and 2: 1). All around, with increased stability and toxicity, AMCs are emerging as contaminants of concern and demand immediate attention to devise methods for their removal.

Imipenem toxicity in male reproductive organs as a result of inflammatory microenvironment and oxidative stress in germinal cells.

Imipenem is a beta-Lactam antibiotic characterized by a broad spectrum of activity. It is prescribed to treat severe infections. Our goal is to investigate toxicity induced in male rat reproductive systems following exposure to this drug (15, 50 or 100 mg/kg) compared to gentamicin (50 mg/kg) treatment. Effects of imipenem on reproductive organ weights, histoarchitecture, sperm parameters, and oxidative stress parameters were evaluated. Serum testosterone levels were measured. Apoptosis and inflammatory behaviors were investigated by immunohistochemical proteins expression analysis of apoptosis regulator BAX (Bax), B-cell lymphoma 2 (Bcl-2), and interleukin-1 beta (IL-1 beta) in testis. Results showed a significant decrease in male fertility parameters including sperm count, sperm motility, reproductive organ weights and serum testosterone levels after imipenem administration as compared to the control and gentamicin treated groups. Increased sperm abnormality was significant in animals treated with high doses of imipenem. Oxidative stress analysis revealed an expressed increase in lipid peroxidation and carbonyl groups levels in testicular tissues compared to control. Similar results were observed with superoxide dismutase and catalase activities from testicular tissues. In addition, severe testicular lesions were observed in the seminiferous tubules as well as important impairments in spermatogenesis testifying an inflammatory microenvironment confirmed by the intensive expression of IL1-beta and Bax protein by germinal cells and Bcl-2 by Leydig cells. In conclusion, imipenem treatment with high doses was found to lead to oxidative stress in male reproductive organs and an inflammatory microenvironment leading to spermatogenesis dysfunction and histopathological changes in the testis.

Therapeutic drug monitoring of imipenem and the incidence of toxicity and failure in hospitalized patients: a retrospective cohort study.

OBJECTIVES: Therapeutic drug monitoring (TDM) of beta-lactam antibiotics is increasingly employed to ensure adequate antibiotic exposure and slow emergence of resistance. Imipenem's therapeutic range has not been defined; we report plasma concentrations and clinical outcomes of patients receiving imipenem for bacterial infections. METHODS: All hospitalized adult patients undergoing imipenem TDM during therapy for suspected or confirmed bacterial infections between 1 January 2013 and 28 February 2017 were included in this single-centre retrospective cohort. The primary outcome was incidence of clinical toxicity; secondary outcomes included incidence of clinical failure and median imipenem concentrations in those with and without toxicity and/or failure. Total imipenem concentrations were measured via high-performance liquid chromatography with ultraviolet detection. RESULTS: A total of 403 imipenem levels were drawn from 300 patients. Fifteen (5%) patients experienced an adverse event considered at least possibly related to imipenem. Eighty-eight (29%) patients had clinical failure; augmented renal clearance appeared to emerge as a protective factor against failure (OR 0.42; 95% CI 0.20-0.89). Median first-measure trough concentration was 3.2 mg/L (IQR 1.7-6.5). Patients with suspected toxicity did not have higher concentrations. Patients whose dose was not increased after a trough level <2 mg/L was returned trended towards increased clinical failure (3/28 (11%) vs. 12/63 (19%)), though the difference was not statistically significant. CONCLUSIONS: Toxicity was rare and clinical failure frequent in this cohort of patients whose imipenem concentrations were generally low and occasionally undetectable. Larger trials are needed to define optimal imipenem exposure.

A carbapenem antibiotic imipenem/cilastatin induces an oxidative stress-status and gonadotoxic effects in « wistar ¼ rats.

Imipenem is a carbapenem antibiotic largely used to treat infection diseases. The present study was designed to investigate the effects of imipenem/cilastatin (IMP) on oxidative stress, antioxidant levels, testicular structure and sperm parameters in rats. Adult Wistar rats (84days old; N=8/group) were treated intraperitoneally with physiological serum containing 0mg/kg, 30mg/kg, 50mg/kg and 80mg/kg of IMP for one week. The results revealed that exposure to IMP especially at high doses, significantly decreased sexual organs weights (testis, epididymis, seminal vesicle and prostate), sperm characteristics (motility, viability and count) and plasma testosterone level while increased sperm abnormality. In addition, the testicular tissue level of lipid peroxidation (LPO) was significantly increased while the level of activities of superoxide dismutase (SOD), catalase (CAT) and glutathion peroxidase (GPx) decreased compared to the control group. Severe testicular lesions were recorded in the seminiferous tubules as well as a significant impairment in sperm characteristics. In conclusion, IMP induced an oxidative stress-status and histopathological changes in the testis and altered spermatogenesis in particular at both 50 and 80mg/kg dose-levels (p<0.001).

Protective effect of morin on the imipenem-induced nephrotoxicity in rabbits.

The present study investigated the protective effect of morin, a natural flavonoid, on the imipenem-induced nephrotoxicity in rabbits. Nephrotoxicity of imipenem was examined after the intravenous administrations of imipenem (200 mg/kg) to rabbits in the presence and the absence of morin (12, 25, 50 mg/kg, p.o.). Cytotoxicity of imipenem was also examined in the presence and the absence of morin (100 microM) by using MDCK cells overexpressing human organic anion transporter 1 and 3 (MDCK/hOAT1 or MDCK/hOAT3). Intravenous dosing of imipenem alone induced severe proximal tubular necrosis in rabbits, however, the concurrent use of morin (25 or 50 mg/kg, p.o.) significantly suppressed the histopathological damage in the kidney induced by imipenem. While imipenem was not cytotoxic in MDCK/hOAT1 cells over the tested concentrations up to 10 mM, it showed significant cellular toxicity with CC(50) of 0.77 mM in MDCK/hOAT3 cells, implying that OAT3 may involve more actively in the imipenem-induced nephrotoxicity. In addition, the cellular toxicity of imipenem decreased by approximately 20 folds in the presence of morin in MDCK/hOAT3 cells. In conclusion, the present study suggests that morin might be beneficial to reduce the nephrotoxicity of imipenem, at least in part, via the inhibition of OAT3-mediated renal excretion of imipenem.

Induction of audiogenic seizures in imipenem/cilastatin-treated rats.

We investigated the effect of intense audiogenic stimulation (AGS) on rats treated with the antibiotic imipenem and dipeptidase inhibitor cilastatin (Imi/Cil). Under pentobarbital anesthesia (40 mg/kg) adult male Wistar rats were implanted with electrodes and cannulas were placed in the right lateral ventricle. Animals were divided into the following groups: (1) vehicle, (2) Imi/Cil 10 microg/10 microg, (3) Imi/Cil 25 microg/25 microg, (4) vehicle+AGS, (5) Imi/Cil 10 microg/10 microg +AGS, and (6) Imi/Cil 25 microg/25 microg +AGS. Imi/Cil was administered intracerebroventricularly in 5 microl of physiological saline. AGS (100+/-3 dB, 60 seconds) was applied at 15-minute intervals after the injection. Imi/Cil-induced seizures (twitching, forelimb clonus, headnodding, rearing, and clonic convulsions) and Imi/Cil-audio-induced seizures (wild running, clonic and tonic convulsions) were scored according to appropriate rating scales. Imi/Cil provoked convulsions dose-dependently. Each behavioral seizure response had a characteristic EEG correlate. AGS by itself did not provoke seizures in untreated rats. Sound stimulation in Imi/Cil-injected rats elicited typical audiogenic seizures, which were induced during five AGS tests (75 minutes postinjection). In most cases audiogenic seizures were not associated with epileptiform activity in the EEG, indicating that spreading of seizures did not involve the cortex. Since Imi/Cil-induced and Imi/Cil-audio-induced seizures differed behaviorally and electroencephalographically, it is suggested that different neural pathways are responsible for these two types of seizures: neuronal networks in the cortex are involved in Imi/Cil-induced seizures, whereas audiogenic seizures use networks residing primarily in the brainstem.

Effects of manipulation of N-methyl-D-aspartate receptors on imipenem/cilastatin-induced seizures in rats.

BACKGROUND & OBJECTIVES: Epileptic seizures have been reported in patients on imipenem/cilastatin (Imi/Cil) therapy. To investigate contribution of N-methyl-D-aspartate (NMDA) receptors in inducing imipenem/cilastatin (Imi/Cil) seizures, the effects of competitive NMDA antagonist, APV [(+/-)-2-amino-5-phosphonovaleric acid], non-competitive NMDA antagonist remacemide [(+/-)-2-amino-N-(1-methyl-1,2-diphenylethyl)-acetamidel, and glycine receptor partial agonist HA-966 [(+/-)-(3-amino-1-hydroxypyrrolid-2-one)] on electroencephalographic (EEG) activity and behaviour were studied in rats. METHODS: Adult male Wistar albino rats were implanted with electrodes and cannulae were placed into the right lateral ventricle. Animals were divided into five groups: (i) saline (icv)+Imi/Cil (ii) APV (0.2 micromol)+Imi/Cil, (iii) APV (0.4 micromol)+Imi/Cil, (iv) remacemide (100 mg/kg, ip)+Imi/Cil, and (v) HA-966 (200 microg, icv)+Imi/Cil. The drugs were administered 30 min before icv injection of Imi/Cil (100/100 microg), and their effects on incidence of seizures, latencies to EEG changes and convulsions, severity, lethality and time to lethal outcome were studied. RESULTS: Imi/Cil provoked complete seizure response in all rats and all animals died within 10-18 min after the injection. EEG epileptiform activity preceded behavioral seizures. Clonic-tonic seizures were characterized by continuous bursts of high frequency high amplitude spikes in the EEG. The dose of 0.2 micromol of APV prolonged only the latency to the first EEG changes, while 0.4 micromol dose significantly influenced all seizure parameters. HA-966 increased only the latency to Imi/Cil-induced convulsions, while remacemide had no significant effect on seizure parameters. INTERPRETATION & CONCLUSION: The results suggested that excitatory neurotransmission contributed to the generation and/or propagation of Imi/Cil-induced seizures in rats, and that the effects of NMDA antagonists depended on a particular binding site within the NMDA receptor complex, and affinity to that site.

[Drug interactions between nonsteroidal anti-inflammatory drug and pazufloxacin mesilate, a new quinolone antibacterial agent for intravenous use: convulsions in mice after intravenous or intracerebroventricular administration].

Convulsant activity of pazufloxacin mesilate (PZFX mesilate), a new quinolone antibacterial agent for intravenous use, in combination with nonsteroidal anti-inflammatory drug (NSAID) was investigated in mice after intravenous or intracerebroventricular administration. Following results were obtained. 1. In combination with 4-biphenylacetic acid (BPAA) at an oral dose of 100 mg/kg, PZFX mesilate did not induce any convulsions at intravenous doses up to 200 mg/kg. Reference quinolones induced convulsions at the following intravenous doses: Enoxacin (ENX), 3.13 mg/kg or more; norfloxacin (NFLX) and lomefloxacin (LFLX), 6.25 mg/kg or more; ciprofloxacin (CPFX), 50 mg/kg or more; sparfloxacin (SPFX) and temafloxacin (TMFX), 100 mg/kg or more; fleroxacin (FLRX), 200 mg/kg. 2. PZFX mesilate at an intravenous dose of 50 mg/kg did not induce convulsions in mice after oral administration of any of 14 kinds of NSAIDs. It induced convulsions at 200 mg/kg in combination with aspirin at an oral dose of 600 mg/kg, while it did not with the other 13 kinds of NSAIDs. 3. Convulsion-inducing dose of PZFX mesilate after intracerebroventricular administration was 100 mg/body, which was higher than those of reference quinolones (NFLX, CPFX, ENX, LFLX, TMFX, levofloxacin, ofloxacin, FLRX and SPFX) and beta-lactam antibiotics (penicillin G, cefazoline, imipenem/cilastatin and panipenem/betamipron). In addition, concurrent dosing of BPAA (1 microgram/body) did not reduce the convulsion-inducing dose of PZFX mesilate. These results suggest that PZFX mesilate has remarkably weak convulsant activity.

Low convulsive activity of a new carbapenem antibiotic, DK-35C, as compared with existing congeners.

Since carbapenems and cephalosporins have been suggested to induce convulsive side effects through an inhibitory action on the central gamma-aminobutyric acid (GABA)-mediated inhibitory transmission, the present study evaluated the convulsive activity of a new carbapenem antibiotic (1R,5S,6S)-6[(R)-1-hydroxyethyl]-2-[(3S,5S)-5(S-methyl-4thiomorpholin ylcarbonyl)pyrrolidin-3-thio]-l-methylcarbapen-2-em-3- carboxylic acid (DK-35C) in in vitro and in vivo experiments, in comparison with cefazolin, imipenem and meropenem. In in vitro experiments, their abilities to inhibit [3H]muscimol (5 nM) binding to GABA(A) receptors were measured using crude synaptic membranes prepared from the rat cerebral cortex. The concentrations (mM) of the antibiotics which inhibit 50% of the specific binding, were 0.6 for imipenem, 1.8 for cefazolin, 15.4 for DK-35C and 27.6 for meropenem. In in vivo experiments, intracerebroventricular (i.c.v.) injections of cefazolin, imipenem and DK-35C induced convulsions in a dose-dependent manner in rats. The doses (nmol/rat) of the antibiotics which induce convulsions in 50% of rats, were 57 for imipenem, 96 for cefazolin, 377 for DK-35C and >3000 for meropenem. In the mouse pentylenetetrazole (PTZ) convulsive model, intravenous pretreatment with cefazolin (800 mg/kg) or imipenem (200 mg/kg) shifted the dose-response curve of PTZ (i.p.) to the left, indicating enhancement of the convulsive activity of PTZ. However, pretreatment with cefazolin, meropenem or DK-35C at a dose of 400 mg/kg did not produce any marked effects on the convulsive activity of PTZ compared with the saline vehicle-pretreated control. The results clearly demonstrate a good correlation between in vitro GABA(A) receptor binding assay and in vivo i.c.v. convulsive model using rats, and suggest that DK-35C may possess a relatively weak convulsive activity mediated through an interaction with GABA(A) receptors.

Nephrotoxic and peroxidative potential of meropenem and imipenem/cilastatin in rat and human renal cortical slices and microsomes.

BACKGROUND: Carbapenems are a relatively new class of beta-lactam antibiotics characterized by a broad spectrum of antibacterial activity. Meropenem (MER), a new carbapenem has shown a lower nephrotoxic potential compared to imipenem (IMI). IMI is used in a fixed one-to-one combination with the nephroprotective agent cilastatin (CIL). The present studies examined whether MER and IMI/CIL produce peroxidative and nephrotoxic alterations including oxidative changes in rat and human renal cortical slices and microsomes. MATERIALS AND METHODS: Untreated slices and microsomes were incubated in vitro for various periods of time in phosphate-buffered media containing various concentrations of MER, IMI/CIL or for comparison cephaloridine (CPH). Lipid peroxidation was monitored by the determination of malondialdehyde (MDA) in incubation media and slices in the presence or absence of antioxidants. Total glutathione, oxidized glutathione (GSSG), pyruvate-stimulated gluconeogenesis and paraaminohippurate (PAH) accumulation were measured in slices. RESULTS: In rat renal cortical slices, MER, IMI/CIL and CPH induced a time- and concentration-dependent MDA production (content in incubation media plus slices). 5 mM MER, 5 mM IMI/CIL and 3 mM CPH were the lowest concentrations which caused a significant MDA production after 3 hs compared to control (control 61.5+/-15.3 nmol MDA/g tissue, MER 75.4+/-10.9, p<0.001; control 48.0+/-8.7, IMI/CIL 65.1+/-11.7, p<0.001; control 61.5+/-15.3, CPH 113.0+/-28.2, p<0.001). 20 mM MER, 20 mM IMI/CIL and 12 mM CPH revealed marked MDA production after 3 hs in human renal cortical slices (control 29.8+/-4.2 nmol MDA/g tissue, MER 49.4+/-8.7, p<0.01; control 27.6+/-7.0, IMI/CIL 68.3+/-9.9, p<0.001; control 32.5+/-7.7, CPH 93.8+/-31.6, p<0.001) and in human renal microsomes (control 1.0+/-0.9 nmol MDA/mg protein, MER 2.9+/-1.0, p<0.05; IMI/CIL 6.8+/-2.2, p<0.001; CPH 8.4+/-2.2, p<0.001), respectively. The corresponding MDA production was about 2-fold higher in rat renal cortical slices and almost the same in rat renal microsomes. Antioxidants reduced the MER-induced increase in MDA content in rat renal cortical slices by 48% (alpha-tocopherol, 10(-4) M), 72% ((+)-cyanidanol-3, 10(-5) M) and 100% (DPPD, N, N'-diphenyl-p-phenylendiamine, 10(-6) M). In rat renal cortical slices, MER and IMI/CIL induced an increase up to 50% in the content of GSSG and a corresponding %-decrease in reduced glutathione (GSH). In rat renal cortical slices, MER and IMI/CIL induced a time- and concentration-dependent decrease in PAH accumulation and gluconeogenesis. PAH accumulation was already reduced by 5 mM MER after 1 h (control slice to medium ratio 18.3+/-6.8, MER 10.7+/-1.9, p<0.05) and by 10 mM IMI/CIL after 3 h (control 16.9+/-5.6, IMI/CIL 5.5+/-1.3, p<0.001). Pyruvate-stimulated gluconeogenesis after 3 hs was already reduced by 2.5 mM MER (control 5.7+/-2.1 micromol glucose/g tissue/h, MER 3.9+/-1.1, p<0.05) and by 10 mM IMI/CIL (control 5.7+/-2.1, IMI/CIL 2.8+/-1.0, p<0.001). CONCLUSION: Thus, MER and IMI/CIL (at concentrations more than 10-fold higher as peak plasma concentrations achieved in humans) revealed an oxidative change (depletion of GSH, production of GSSG), a peroxidative potential (production of MDA) and a nephrotoxic potential (reduction in pyruvate-stimulated gluconeogenesis and PAH accumulation). Human kidney seems to be less susceptible to beta-lactam antibiotic-induced lipid peroxidation than rat kidney.

[Nephrotoxicity and drug interaction of vancomycin].

We examined drug interactions of vancomycin hydrochloride (VCM) in the rabbit kidney. VCM has an antibacterial action against Gram positive bacteria, but composite infection patients must be jointly treated with antibiotics that are effective on Gram negative bacteria, e.g., imipenem (IPM)-cilastatin sodium (CS) compounding agent. Both VCM and IPM have the adverse reaction of nephrotoxicity, whereas CS restrains the nephrotoxicity of IPM. To clarify the interactions, we examined the nephrotoxicity and pharmacokinetics of VCM in the rabbit and compared them with those in rabbits administered VCM with CS or IPM-CS. Symptoms of nephrotoxicity such as an increase of serum creatinine concentration and BUN and a morphological change of the kidney were observed with iv. injection of VCM at 300 mg/kg. However, no abnormality of clinical data and morphological alteration were observed in the groups injected with VCM plus CS or IPM-CS. Clearance and urinary excretion of VCM obviously increased in the groups injected with VCM plus CS or IPM-CS. In addition, it was estimated that VCM was actively transported by observation of the uptake in rabbit renal slices. Furthermore, the uptake rate of VCM in the renal cortex was significantly decreased by CS. Together with the above findings, it is suggested that the restraint effect of VCM uptake into nephrocytes by CS is one of the decreasing mechanisms of the nephrotoxic effect of VCM.

Structural features resulting in convulsive activity of carbapenem compounds: effect of C-2 side chain.

The neurotoxicity of meropenem was much lower than that of both imipenem and panipenem after intraventricular administration to mice. To clarify the major structural features responsible for the induction of convulsions by carbapenem antibiotics, the structure-activity relationship on convulsant activity was investigated in N-acetyl-2-pyrroline and cyclopentene derivatives which correspond to the 5-membered ring containing the C-2 side chain of carbapenem antibiotics. Among these derivatives, compounds with strong basicity in the side chain showed convulsant activity similar to that of the parent carbapenem compounds. In addition to the strength of the basicity of the amino group, the distance from the carboxyl to the amino group and steric crowding around the amino group also appeared to play an important role in the induction of convulsions. The results of gamma aminobutyric acid (GABAA) receptor binding assays indicated that the induction of convulsions was caused predominantly by the inhibition of GABAA-mediated inhibitory transmission. However, the in vivo convulsant activity of some of these compounds did not correlate with their in vitro inhibitory effect on GABAA receptor binding.

Correlation between in vitro and in vivo models of proconvulsive activity with the carbapenem antibiotics, biapenem, imipenem/cilastatin and meropenem.

The present study evaluated the proconvulsant liability of biapenem, a novel carbapenem antibiotic, in in vitro and in vivo experiments, in comparison with the carbapenems, imipenem/cilastatin and meropenem. Imipenem/cilastatin is a carbapenem antibiotic with known proconvulsive liability in man and in animal experiments. In in vivo studies imipenem/cilastatin, at doses of 400/400 mg/kg i.v., significantly lowered the convulsive threshold of pentylenetetrazol (PTZ) in mice and shifted the dose-response curve of PTZ. The effects of biapenem (400 mg/kg i.v.) and another reference carbapenem, meropenem (400 mg/kg i.v.), in the mouse PTZ model were not significantly different from control. In in vitro experiments the carbapenems were tested for their ability to inhibit [3H]muscimol (1.3 mM) binding to rat brain homogenates at concentrations of 1-10 mM. Similar to in vivo results, when compared to imipenem/cilastatin, biapenem and meropenem did not inhibit [3H]muscimol binding to the GABAA receptor complex in brain homogenates while imipenem/cilastatin exhibited significant inhibition (IC50 = 4.6 mM). These results further confirm the correlation between in vitro GABAA binding and in vivo PTZ convulsive testing with carbapenem antibiotics, and suggest that biapenem possesses a low proconvulsive liability.

Preventive effect of betamipron on nephrotoxicity and uptake of carbapenems in rabbit renal cortex.

The preventive effect of betamipron (N-benzoyl-3-propionic acid: BP) on the renal uptake and nephrotoxicity of carbapenems (panipenem and imipenem) was studied in rabbits. Panipenem, a new carbapenem antibiotic, induced nephrotoxicity at a dose of 200 mg/kg, i.v., but this was less severe than that caused by a single dose of imipenem or cephaloridine. Along with the significant reduction of nephrotoxicity, the uptake of these carbapenems in the renal cortex was remarkably inhibited by simultaneous treatment with BP (200 mg/kg, i.v.). These results suggest that BP reduces the nephrotoxicity of carbapenems through inhibiting the active transport of carbapenems in the renal cortex. Because of the low toxicity of BP (LD50 in the rat, more than 3,000 mg/kg, i.v.), it was concluded that BP might be a good candidate for reducing the nephrotoxicity induced by panipenem or imipenem.

Effects of some quinolones on imipenem-induced seizures in DBA/2 mice.

1. The behavioural and convulsant effects of imipenem, a carbapenem derivative, were studied after i.p. administration in DBA/2 mice, a strain genetically susceptible to sound-induced seizures and in Swiss mice. 2. It was found that DBA/2 mice were more susceptible to seizures induced by imipenem than Swiss mice. 3. The proconvulsant effects of some quinolones were also evaluated in DBA/2 mice on seizures evoked by means of i.p. administration of imipenem. The present study demonstrated that the order of proconvulsant activity in our epileptic model was pefloxacin > enoxacin > ofloxacin > nalidixic acid > rufloxacin > norfloxacin > ciprofloxacin > cinoxacin > temafloxacin. 4. The relationship between the chemical structure and the proconvulsant activity of quinolone derivatives was studied. The relationship between the lipophilicity and the proconvulsant activity was also investigated. 5. Although the main mechanism for seizure potentiation cannot be easily determined potential drug interactions exist. It has been reported that imipenem and quinolones are all believed to increase excitation of the central nervous system by inhibition of GABA binding to receptors. 6. A slow clearance from the central nervous system and from the kidney may also occur following the concomitant administration of some quinolones and imipenem.

Genetic definition of the substrate selectivity of outer membrane porin protein OprD of Pseudomonas aeruginosa.

Earlier studies proved that Pseudomonas aeruginosa OprD is a specific porin for basic amino acids and imipenem. It was also considered to function as a nonspecific porin that allowed the size-dependent uptake of monosaccharides and facilitation of the uptake of quinolone and other antibiotics. In the present study, we utilized P. aeruginosa strains with genetically defined levels of OprD to characterize the in vivo substrate selectivity of this porin. An oprD::omega interposon mutant was constructed by gene replacement utilizing an in vitro mutagenized cloned oprD gene. In addition, OprD was overexpressed from the lac promoter by cloning the oprD gene into the broad-host-range plasmid pUCP19. To test the substrate selectivity, strains were grown in minimal medium with limiting concentrations of the carbon sources glucose, gluconate, or pyruvate. In minimal medium with 0.5 mM gluconate, the growth rates of the parent strain H103 and its oprD::omega mutant H729 were only 60 and 20%, respectively, of that of the OprD-overexpressing strain H103(pXH2). In contrast, no significant differences were observed in the growth rates of these three strains on glucose or pyruvate, indicating that OprD selectively facilitated the transport of gluconate. To determine the role of OprD in antibiotic uptake, nine strains representing different levels of OprD and OprF were used to determine the MICs of different antibiotics. The results clearly demonstrated that OprD could be utilized by imipenem and meropenem but that, even when substantially overexpressed, it could not be significantly utilized by other beta-lactams, quinolones, or aminoglycosides. In addition, competition experiments confirmed that imipenem had common binding sites with basic amino acids in the OprD channel, but not with gluconate or glucose.

Drug-induced retinal toxicity in albino rabbits: the effects of imipenem and aztreonam.

PURPOSE: To test the toxic action of two antibiotics, imipenem and aztreonam, on the functional and morphologic integrity of the albino rabbit retina. METHODS: Two commercial drugs were used--Tienam, which contains imipenem, and Azactam, which contains aztreonam. Different doses of these drugs were injected intravitreally. Retinal function was assessed from the electroretinogram (ERG) and the visual evoked potential (VEP). Retinal structure was examined at the light microscopic level. RESULTS: Imipenem did not affect the ERG and the VEP responses or the morphology of the retina up to a total injected dose of 0.98 mg (2 mg Tienam). Aztreonam was not toxic to the albino rabbit retina up to a total injected dose of 2.8 mg (5 mg of Azactam). Severe functional and morphologic retinal damage was seen when 10 mg of Azactam was injected. A similar degree of damage was seen when a dose of 5 mg L-arginine, an ingredient of Azactam, was injected into the vitreous. CONCLUSIONS: Imipenem and aztreonam are nontoxic to the albino rabbit retina at concentrations that are 500-fold higher than their effective dose against bacterial infection. Azactam is highly toxic at high levels (more than 10 mg injected into the vitreous). Most of the toxicity could be explained by the L-arginine content of the drug.

Two-dimensional polyacrylamide gel electrophoresis isolation and microsequencing of Pseudomonas aeruginosa proteins.

Outer membrane (OM) proteins of beta-lactam-susceptible and -resistant strains of Pseudomonas aeruginosa were analyzed by 2-D polyacrylamide gel electrophoresis. Carrier ampholytes, pH 4-8, and immobilized pH gradient (IPG), pH 3.5-10.0, procedures were used. An acidic-protein spot (pI = 5.2) detected in susceptible but not in an imipenem-resistant strain was sequenced and twenty-five N-terminal amino acids had total homology with the OM protein D, the imipenem-specific porin of P. aeruginosa. A basic-protein spot (pI = 9.0) detected in ceftazidime-resistant, but not in a susceptible strain was sequenced and fourteen N-terminal amino acids had homology with a beta-lactamase encoded by the ampC gene of P. aeruginosa. The IPG procedure allows identification of more than one hundred proteins of the OM fraction from a single gel. Detection of beta-lactamase in OM fractions might reflect a periplasmic contamination, but its anchorage within the OM cannot be ruled out.