Evaluation of Meropenem Pharmacokinetics in an Experimental Acute Respiratory Distress Syndrome (ARDS) Model during Extracorporeal Membrane Oxygenation (ECMO) by Using a PenP β-Lactamase Biosensor

INTRODUCTION

The use of antibiotics is mandatory in patients during extracorporeal membrane oxygenation (ECMO) support. Clinical studies have shown high variability in the antibiotic concentrations, as well as sequestration of them by the ECMO circuit, suggesting that the doses and/or interval administration used during ECMO may not be adequate. Thus, a fast response sensor to estimate antibiotic concentrations in this setting would contribute to improve dose adjustments. The biosensor PenP has been shown to have a dynamic range, sensitivity and specificity useful for pharmacokinetic (PK) tests in healthy subjects. However, the use of this biosensor in the context of a complex critical condition, such as ECMO during acute respiratory distress syndrome (ARDS), has not been tested.

OBJECTIVES

To describe, by using PenP Biosensor, the pharmacokinetic of meropenem in a 24-h animal ARDS/ECMO model.

METHODS

The PK of meropenem was evaluated in a swine model before and during ECMO.

RESULTS

The PK parameters such as maximum concentration (Cmax), elimination rate constant (Ke), and cleareance (Cl), were not significantly altered during ECMO support.

CONCLUSIONS

(a) ECMO does not affect the PK of meropenem, at least during the first 24 h; and (b) PenP has the potential to become an effective tool for making medical decisions associated with the dose model of antibiotics in a critical patient context.

Photochemical degradation of the carbapenem antibiotics imipenem and meropenem in aqueous solutions under solar radiation

This paper deals with the photochemical fate of two representative carbapenem antibiotics, namely imipenem and meropenem, in aqueous solutions under solar radiation. The analytical method employed for the determination of the target compounds in various aqueous matrices, such as ultrapure water, municipal wastewater treatment plant effluents, and river water, at environmentally relevant concentrations, was liquid chromatography coupled with hybrid triple quadrupole-linear ion trap-mass spectrometry. The absorption spectra of both compounds were measured in aqueous solutions at pH values from 6 to 8, and both compounds showed a rather strong absorption band centered at about 300 nm, while their molar absorption coefficient was in the order from 9 × 10³-10⁴ L mol^-1 cm^-1. The kinetics of the photochemical degradation of the target compounds was studied in aqueous solutions under natural solar radiation in a solar reactor with compound parabolic collectors. It was found that the photochemical degradation of both compounds at environmentally relevant concentrations follows first order kinetics and the quantum yield was in the order of 10^-3 mol einsten^-1. Several parameters were studied, such as solution pH, the presence of nitrate ions and humic acids, and the effect of water matrix. In all cases, it was found that the presence of various organic and inorganic constituents in the aqueous matrices do not contribute significantly, either positively or negatively, to the photochemical degradation of both compounds under natural solar radiation. In a final set of photolysis experiments, the effect of the level of irradiance was studied under simulated solar radiation and it was found that the quantum yield for the direct photodegradation of both compounds remained practically constant by changing the incident solar irradiance from 28 to 50 W m^-2.

Stability of generic brands of meropenem reconstituted in isotonic saline

BACKGROUND

Meropenem is a relatively unstable compound when dissolved. Currently, all available data have been derived from tests on the original product from Astrazeneca, and it is unsure if these data can be extrapolated to the stability of other commercially available vials. The aim of this study was therefore to assess the stability of four different brands of meropenem to be used as a prolonged or continuous infusion.

METHODS

Commercially available meropenem vials were reconstituted and mixed with 0.9% sodium chloride to produce solutions with concentrations of 10.20 and 40 mg/mL in polypropylene syringes, which were kept at 25 °C. Samples were taken immediately after preparation and up to 12 hours. Solutions retaining >90% of the initial concentration were considered stable.

RESULTS

The stability was concentration-dependent. At 25 °C, all 10 and 20 mg/mL solutions were stable for 12 hours in 0.9% sodium chloride, while the 40 mg/mL solutions were stable for a maximum of 8 hours. Stability of the different vials of meropenem was comparable for the time period tested (related samples Friedman's two way of analysis of variance by ranks, P=0.282).

CONCLUSION

All tested commercially available vials of meropenem in a concentration of 10 and 20 mg/mL were stable for 12 hours at 25 °C when diluted in 0.9% sodium chloride. The 40 mg/mL solutions were stable for a maximum of 8 hours. This report is the first to show equivalent stability between different commercially available vials of meropenem.

[Experimental study on concentrations and pharmacokinetics of antibiotics in bile and evaluation of their microbicidal potential]

OBJECTIVE

To study the concentrations and pharmacokinetics of 6 different kinds of antibiotics in rabbit bile, and evaluate their microbicidal potential.

METHODS

Thirty-six health rabbits were randomly divided into 6 groups, and each group was 6 rabbits. After anaesthesia, the common bile duct of rabbit was isolated and cumulated with a silicone tube. The rabbits were administered intravenously with the equal-effect dose of antibiotics. Bile (1.5 ml) was collected at different time points after administration, and the concentration of antibiotics of bile was assayed by high performance liquid chromatography. The bile drug concentration-time data were processed by software to figure out the pharmacokinetic parameters such as maximum concentration (C(max)), peak time (T(max)), half-life time (T(1/2)), clearance (CL) and apparent volume of distribution (VD). The bile antibiotics concentration contrasted to the minimum inhibitory concentration (MIC), and attained the bactericidal index (C(max)/MIC) and the time when the drug concentration exceeded the MIC (T(>MIC)).

RESULTS

The C(max) and T1/2 of each antibiotic were as the followings: piperacillin (7 950 ± 3 023) mg/L and (1.97 ± 1.23) h, ceftriaxone (1 104 ± 248) mg/L and (3.14 ± 0.57) h, cefoperazone (5 215 ± 2 225) mg/L and (0.89 ± 0.13) h, meropenem (31.97 ± 12.44) mg/L and (0.36 ± 0.11) h, levofloxacin (66.3 ± 36.9) mg/L and (3.32 ± 2.57) h, metronidazole (28.2 ± 10.2) mg/L and (0.81 ± 0.33) h, respectively. Piperacillin/tazobactam and cefoperazone/sulbactam had the largest bactericidal index and the longest T(>MIC), and their bactericidal indexes were (62.1 ± 23.6) - (993.8 ± 377.9) and (164.8 ± 69.0) - (659.3 ± 275.9), their T(>MIC) were (6.00 ± 2.53) - (8.00 ± 0.00) h and (6.33 ± 1.97) - (8.00 ± 0.00) h. The bactericidal index and T(>MIC) of levofloxacin were the smallest, which were (2.1 ± 1.2) - (8.3 ± 4.6) and (0.54 ± 0.25) - (2.67 ± 1.03) h . Ceftriaxone and meropenem were as the medium, and their bactericidal indexes and T(>MIC) were (4.3 ± 1.0) - (69.2 ± 15.5) , (1.42 ± 0.65) - (8.00 ± 0.00) h and (2.0 ± 0.8) - (1 031.3 ± 401.4) , (0.29 ± 0.10) - (1.83 ± 0.26) h. The bactericidal index of metronidazole to anaerobic ranged from 7.4 to 294.9, and the T(>MIC) ranged from 1.88 to 5.00 h.

CONCLUSIONS

The bile concentrations of six antibiotics all exceed their effective bactericidal concentrations. The concentration-time curves of piperacillin, cefoperazone, meropenem and metronidazole conformed to one-compartment model, and ceftriaxone and levofloxacin are conformed to two-compartment model. Piperacillin/tazobactam and cefoperazone/sulbactam have the largest bactericidal index and the longest T(>MIC), so they can be chosen as the first choice for the therapy of hepatobiliary infection.For the anaerobic, the microbicidal potential of metronidazole is high.

The effect of borneol on the concentration of meropenem in rat brain and blood

Meropenem is a carbapenem antibiotic with a wide spectrum of activity against both Gram-positive and Gram-negative bacteria. Because of its clinical efficacy, meropenem is an excellent choice for the treatment of serious infections in both adults and children. The knowledge of tissue concentrations of antibiotic in an infection site is valuable for the prediction of treatment outcome. The aim of the present study is to investigate the effect of borneol on the concentration of meropenem in rat brain and blood and to find the potential relationships of the combined use of medicine and traditional Chinese medicine. Analysis of meropenem in the dialysates was achieved using the microdialysis technique and HPLC. At 40 min after the administration of an intraperitoneal injection of meropenem, the concentration of meropenem in brain in borneol+meropenem group was 2.25 (0.35) μg ml(-1), which was significantly higher than that in meropenem group [1.20 (0.12) μg ml(-1); P < 0.01]. Within 80 min of drug administration, the AUCbrain/AUCblood (area under the curve, AUC) in the borneol+meropenem group was 1.2 times that of the meropenem group. Borneol can increase the concentration of meropenem in the cerebrospinal fluid, but has no influence on its blood concentration. This study represents a successful application of the microdialysis technique, which is an effective method for the study of pharmacokinetics of meropenem.

Ultraviolet spectrophotometry (dual wavelength and chemometric) and high performance liquid chromatography for simultaneous estimation of meropenem and sulbactam sodium in pharmaceutical dosage form

UV spectrophotometric and high performance liquid chromatography (HPLC) methods were developed for simultaneous determination of meropenem (MERM) and sulbactam sodium (SB) in injection. UV spectrophotometric methods were developed using 0.1N sodium hydroxide as solvent. The Beer's plot for dual wavelength method was linear in the range of 4-24 μg mL(-1) and 2-12 μg mL(-1) for MERM and SB, respectively. The percent recoveries were found to be 98.52±1.23% for MERM and 101.45±1.1% for SB. Chemometrics assisted UV spectrophotometry was performed using Partial Least Square (PLS) analysis model and Principal Component Regression (PCR) analysis model. The % recoveries of the MERM were found to be 100.61±0.06% and 101.31±0.12% using PLS and PCR, respectively. The % recoveries of the SB were found to be 98.29±0.09% and 97.61±0.13% using PLS and PCR, respectively. Chromatography was performed on Hypersil BDS C18 column using methanol:acetonitrile:water (10:20:70 v/v/v) as mobile phase. The retention times of MERM and SB were found to be 2.9 min and 2.25 min, respectively. Developed HPLC method was found to be linear in the range of 50-250 μg mL(-1) and 25-125 μg mL(-1) for MERM and SB, respectively. The % recoveries were found to be 98.85±0.25% and 98.63±0.34% for MERM and SB, respectively. The developed analytical methods did not show any interference of the excipients when applied to pharmaceutical dosage form.

Development and validation of stability-indicating HPLC method for simultaneous determination of meropenem and potassium clavulanate

A stability-indicating LC assay method was developed and validated for a simultaneous determination of meropenem and potassium clavulanate in the presence of degradation products formed during acid-base hydrolysis, oxidation and thermolysis. The isocratic RP-HPLC method was developed with a LiChrospher RP-18 (250 mm x 4.6 mm, 5 microm) column and gradient elution of 12 mmol/L ammonium acetate and acetonitrile. The flow rate of the mobile phase was 1.0 mL/min, the detection wavelength 220 nm and the temperature 303 K. The method was validated with regard to linearity, accuracy, precision, selectivity and robustness, and was applied successfully for the determination of meropenem and potassium clavulanate separately as well as jointly in pharmaceutical formulations.

The use of UV, FT-IR and Raman spectra for the identification of the newest penem analogs: solutions based on mathematic procedure and the density functional theory

The application of ultraviolet, FT-IR and Raman spectra was proposed for identification studies of the newest penem analogs (doripenem, biapenem and faropenem). An identification of the newest penem analogs based on their separation from related substances was achieved after the application of first derivative of direct spectra in ultraviolet which permitted elimination of overlapping effects. A combination of experimental and theoretical studies was performed for analyzing the structure and vibrational spectra (FT-IR and Raman spectra) of doripenem, biapenem and faropenem. The calculations were conducted using the density functional theory with the B3LYP hybrid functional and 6-31G(d,p) basis set. The confirmation of the applicability of the DFT methodology for interpretation of vibrational IR and Raman spectra of the newest penem analogs contributed to determination of changes of vibrations in the area of the most labile bonds. By employing the theoretical approach it was possible to eliminate necessity of using reference standards which - considering the instability of penem analogs - require that correction coefficients are factored in.

Microbiological assay for the determination of meropenem in pharmaceutical dosage form

Meropenem is a highly active carbapenem antibiotic used in the treatment of a wide range of serious infections. The present work reports a microbiological assay, applying the cylinder-plate method, for the determination of meropenem in powder for injection. The validation method yielded good results and included linearity, precision, accuracy and specificity. The assay is based on the inhibitory effect of meropenem upon the strain of Micrococcus luteus ATCC 9341 used as the test microorganism. The results of assay were treated statistically by analysis of variance (ANOVA) and were found to be linear (r=0.9999) in the range of 1.5-6.0 microg ml(-1), precise (intra-assay: R.S.D.=0.29; inter-assay: R.S.D.=0.94) and accurate. A preliminary stability study of meropenem was performed to show that the microbiological assay is specific for the determination of meropenem in the presence of its degradation products. The degraded samples were also analysed by the HPLC method. The proposed method allows the quantitation of meropenem in pharmaceutical dosage form and can be used for the drug analysis in routine quality control.

Chromatographic determination of polymerized impurities in meropenem

A method for the separation of polymerized impurities in meropenem has been developed by gel filtration chromatography (GFC). The chromatographic conditions included a Superdex peptide HR 10/30 column and the mobile phase consisting of 0.01 mol L(-1) sodium phosphate buffer (pH 7.0), at a flow rate of 0.8 mL min(-1). The wavelength of UV detector was set at 220 nm. The linear range was 0.08-10 microg (r=0.9998); relative standard deviation (R.S.D.)=0.5-1.5%; the LOD and LOQ were 2.4 and 12.4 ng, respectively. Specificity of the GFC was checked by switching the effluent of each peak on the GFC to a C18 trap column and analyzing the effluent by LC-MS. The result shows that for the determination of polymers, the gel filtration chromatography is a rather simple separation mode as compared to RPLC.

Validation of HPLC and UV spectrophotometric methods for the determination of meropenem in pharmaceutical dosage form

A high-performance liquid chromatographic method and a UV spectrophotometric method for the quantitative determination of meropenem, a highly active carbapenem antibiotic, in powder for injection were developed in present work. The parameters linearity, precision, accuracy, specificity, robustness, limit of detection and limit of quantitation were studied according to International Conference on Harmonization guidelines. Chromatography was carried out by reversed-phase technique on an RP-18 column with a mobile phase composed of 30 mM monobasic phosphate buffer and acetonitrile (90:10; v/v), adjusted to pH 3.0 with orthophosphoric acid. The UV spectrophotometric method was performed at 298 nm. The samples were prepared in water and the stability of meropenem in aqueous solution at 4 and 25 degrees C was studied. The results were satisfactory with good stability after 24 h at 4 degrees C. Statistical analysis by Student's t-test showed no significant difference between the results obtained by the two methods. The proposed methods are highly sensitive, precise and accurate and can be used for the reliable quantitation of meropenem in pharmaceutical dosage form.

A rapid, sensitive high performance liquid chromatographic method for the determination of meropenem in pharmaceutical dosage form, human serum and urine

A new, simple, precise and rapid high performance liquid chromatographic method was developed for the determination of meropenem in human serum, urine and pharmaceutical dosage forms. Chromatography was carried out on an LC(18) column using a mixture of 15 mM KH(2)PO(4):acetonitrile:methanol (84:12:4; v/v/v), adjusted to pH 2.8 with H(3)PO(4). The proposed method was conducted using a reversed-phase technique, UV monitoring at 307.6 nm and cefepime as an internal standard. The retention times were 5.98 and 7.47 min for cefepime and meropenem, respectively. The detector response was linear over the concentration range of 50-10,000 ng/mL. The detection limit of the procedure was found to be 22 ng/mL. The detection limit for meropenem in human plasma was 108.4 ng/mL and the corresponding value in human urine was 179.3 ng/mL. No interference from endogenous substances in human serum, urine and pharmaceutical preparation was observed. The proposed method is sufficiently sensitive for determination of the concentrations of meropenem and may have clinical application for its monitoring in patients receiving the drug.

Rapid antibiotic drug monitoring: meropenem and ceftazidime determination in serum and bronchial secretions by high-performance liquid chromatography-integrated sample preparation

A sensitive and rapid HPLC assay for the determination of the beta-lactam antibiotics ceftazidime and meropenem in serum and bronchial secretions is described. HPLC-integrated sample preparation allows direct injection of serum samples without any pretreatment. Sputum samples need only a simple homogenisation and volume measurement but no liquefying reagents are necessary. The inline extraction technique is realized by automatically switching from the extraction column to the analytical column. After the matrix passed the extraction column, the retained analyte is quantitatively transferred to the analytical column where separation by isocratic HPLC is performed. Ceftazidime and meropenem are detected according to their absorption maxima at 258 and 296 nm, respectively. The detection limit of both antibiotics is estimated to be better than 0.5 microg/ml in serum as well as in sputum samples. The described procedure allows determination of the antibiotics within 30-45 min, thereby facilitating drug monitoring in clinical routine.

Influence of changes in pancreatic tissue morphology and capillary blood flow on antibiotic tissue concentrations in the pancreas during the progression of acute pancreatitis

BACKGROUND

The ability of an antibiotic to reach bactericidal concentrations in tissue depends on numerous factors including tissue composition and regional perfusion. Although necrotising pancreatitis is characterised by progression of pancreatic necrosis over at least 96 hours and microcirculatory alterations, the impact of these changes on the concentration of antibiotics in the pancreas has not yet been investigated.

AIM

To determine and compare pancreatic tissue concentrations of imipenem and cefotaxime at different stages of acute necrotising pancreatitis in an animal model that has been shown to mimic closely the pathomorphological and bacteriological features of severe human pancreatitis.

METHOD

Acute necrotising pancreatitis was induced in rats by a standardised intraductal infusion of glycodeoxycholic acid and intravenous cerulein. Six hours (n = 16) and 48 hours (n = 16) after induction of pancreatitis, the animals were randomised for intravenous therapy with either imipenem or cefotaxime. Fifteen minutes after injection of the antibiotic, the animals were killed. Blood and the head of the pancreas were collected for determining imipenem or cefotaxime in serum and tissue; the splenic portion of the pancreas was prepared for histological examination. In an additional set of identically treated animals, pancreatic capillary blood flow (PCBF) was assessed by intravital microscopy before induction of acute necrotising pancreatitis and at the time of antibiotic therapy.

RESULTS

Imipenem accumulates in the pancreas in the initial phase of acute necrotising pancreatitis characterised by pronounced oedema and decreased PCBF, and tends to decrease with resolution of the oedema and the progression of acinar cell necrosis in the later course of the disease. Concentrations of cefotaxime are low in oedematous pancreatic tissue early after induction of acute necrotising pancreatitis and increase with the resolution of oedema and normalisation of PCBF.

CONCLUSIONS

Concentrations of antibiotics in the pancreas vary in acute necrotising pancreatitis, depending on changes in pancreatic tissue morphology and capillary blood flow. This suggests that antibiotic tissue concentrations may not be consistent from one agent to another and that efficacy of antibiotics in acute pancreatitis cannot be estimated solely on the basis of their pharmacological and microbiological properties.

Penetration of meropenem into heart valve tissue

Thirty-three patients requiring cardiac valve surgery were administered meropenem 1000 mg by a 5 to 10 min iv injection. Samples of blood, cardiac valve and atrial muscle tissue were removed at valvectomy and analysed for meropenem by high performance liquid chromatography (HPLC) with UV detection. The plasma concentrations observed in the samples from these patients were higher than those reported when meropenem 1000 mg was administered to healthy volunteers by 5 min iv injection. No clinical adverse events attributable to meropenem were reported and the single 1000 mg dose was well tolerated. The penetration of meropenem into cardiac muscle and valve tissue was rapid and in excess of that expected solely on the basis of distribution into extracellular fluid. The concentrations achieved in the tissues were in excess of the MICs of the pathogens commonly causing endocarditis.

A compilation of meropenem tissue distribution data

Meropenem body fluid and tissue concentration data from both published studies and samples obtained during efficacy evaluation have been compiled and presented according to a consistent format to facilitate comparison. The concentration data have been compared with the mode MIC data available for the pathogens isolated during the clinical evaluation of meropenem. These data support the widespread and rapid penetration of meropenem into the interstitial fluid of those tissues not protected by a tight epithelial barrier. Furthermore, they suggest that the proposed dosages of meropenem 500 mg or 1 g tds would provide an adequate duration of cover at tissue sites for the treatment of a range of commonly occurring pathogens. A higher dosage of 40 mg/kg or 2 g in adults given tds would be recommended for meningitis based on the penetration of meropenem into CSF. Overall, the tissue and body fluid data presented confirm the expectation, based on the plasma concentrations and theoretical arguments, that meropenem is rapidly and readily distributed into the interstitial fluid, thereby producing concentrations in tissues likely to be clinically effective. This is consistent with the available clinical data on the therapeutic efficacy of meropenem.

Pharmacokinetics of meropenem in experimentally burned rats

The pharmacokinetics of meropenem were investigated to examine its penetration into the skin of third degree burned rats. The rats were divided into two groups. One group acted as the control, and the other group had third degree burns induced by immersing their backs into 80 degrees C water for 20 seconds. The rats in each group were given 20 mg/kg of body weight of meropenem intravenously by one bolus injection seven days after burn inducement or depilation. In the non-burned control group, the maximum concentrations of meropenem in the serum and skin of 6.03 micrograms/ml and 0.12 microgram/g were respectively obtained 15 minutes after the injection and decreased very rapidly thereafter. In the burned rats, the maximum concentrations of meropenem in the serum, skin (eschar), and exudate fluid of 7.07 micrograms/ml, 1.44 micrograms/g and 5.99 micrograms/ml were respectively obtained 15 minutes after the injection and decreased very slowly. The penetration of meropenem into the burned skin was higher than that into the normal skin. These results suggest that meropenem is a very useful antibiotic in the treatment of burn infection.

Application of high-performance liquid chromatography of some antibiotics in clinical microbiology

During recent years high-performance liquid chromatography has become an excellent tool for the determination of antibiotics in biological fluids. Compared with biological assays, the major benefits of this method are specificity and rapidity. In particular, the determination of biologically inactive metabolites emphasizes that this technique plays an outstanding role for the analysis of antibiotics. This paper describes how the method can be used in the analysis of several antibiotics and demonstrates the efficacy of this method for clinical microbiology. Methods for the determination in biological fluids of acylaminopenicillins (azlocillin, mezlocillin, piperacillin and aspoxicillin), quinolones (ciprofloxacine, norfloxacine and ofloxacine), a penem (imipenem) and a cephalosporin (cefixime) are summarized. Furthermore, their application to in vitro studies and their trial in clinical studies are described.

Compressed pellet X-ray diffraction monitoring for optimization of crystallinity in lyophilized solids: imipenem: cilastatin sodium case

A rapid, quantitative X-ray diffraction method to monitor the relative degree of crystallinity of lyophilized materials is described. The method was applied to determine the degree of crystallinity of imipenem [(5 R, 6 S)-3-[[2(formimidoylamino)ethyl]thio]-6-[(R)-1- hydroxyethyl]-7-oxo-1-azabicyclo[3.2.0]hept-2-ene-2-carboxylic acid] in 60 process related samples of the combination product of imipenem and amorphous cilastatin sodium (sodium (Z)-7-[[(R)-2-amino-2-carboxyethyl]thio]-2-[(S)-2,2- dimethylcyclopropanecarboxamido]-2-heptenoate). This assured optimizing process conditions which affect the improvement of crystallinity.

Degradation kinetics of imipenem in normal saline and in human serum

The stability of imipenem in 0.9% sodium chloride and in human serum was measured at controlled temperatures over time. The degradation was characterized by a first-order process and was consistent with an apparent hydrolysis reaction.

Stability of imipenem in Mueller-Hinton agar stored at 4 degrees C

The purpose of the present study was to measure the stability of imipenem in Mueller-Hinton agar stored at 4 degrees C over time. MICs for Staphylococcus aureus ATCC 25923, Streptococcus faecalis ATCC 29212, Escherichia coli ATCC 25922, and Pseudomonas aeruginosa ATCC 27853 were determined in triplicate daily for up to 15 days. The calculated mean time to observe a shift of one dilution in MIC endpoints was 4.33 +/- 1.25 days. For routine work, imipenem agar dilution plates should be prepared within 48 to 72 h of the test.

Determination of imipenem (N-formimidoyl thienamycin) in human plasma and urine by high-performance liquid chromatography, comparison with microbiological methodology and stability

High-performance liquid chromatographic (HPLC) methods using ultraviolet (UV) detection have been developed for the assay of the antibiotic imipenem (N-formimidoyl thienamycin) in human plasma and urine. A reversed-phase analytical column is employed in the plasma assay method and a cation-exchange column is used in the urine assay method. Both methods use borate buffer in the mobile phase. The method of preparation of human fluid samples for HPLC injection has been optimized with respect to the stability of imipenem in aqueous buffers, in morpholine buffer--ethylene glycol stabilizer, and in urine and plasma. Preparation of the samples before injection into the HPLC systems involves deproteination/filtration of the plasma/urine samples. The open lactam metabolite and the coadministered dehydropeptidase inhibitor, cilastatin sodium, do not interfere with the 313-nm detection of imipenem in either the plasma or the urine assay. Thienamycin, the precursor of imipenem and an impurity in imipenem formulations, is separated from the drug using both of these methods. Concentrations generated from the HPLC analysis of plasma and urine samples from two healthy volunteers compare favorably with results using a microbiological assay method. Correlation of the two methods gives r greater than or equal to 0.990 for both fluids.

Ocular penetration of N-formimidoyl thienamycin (MK-787) and potentiation by dipeptidase inhibitor (MK-791)

N-formimidoyl thienamycin (MK-787) is a new beta-lactam with potent activity against both aerobic and anaerobic gram-positive and gram-negative bacteria. Its spectrum and activity suggest it may be useful in treatment of complicated intraocular infections. Its ocular penetration was studied in New Zealand white rabbits immediately before and after the third dose of 40 mg/kg administered intravenously at q6h intervals. Plasma, aqueous humor, and vitreous humor were obtained by direct aspiration, and antibiotic levels were assayed using an agar well diffusion method. MK-787 penetrated uninflamed intraocular fluids, including vitreous humor, although vitreous concentrations achieved (0.1-0.2 micrograms/ml) were significantly lower than the mean peak plasma (15 micrograms/ml) and aqueous concentrations (7 micrograms/ml). Nevertheless, the intraocular levels attained approached or exceeded the MIC90 for most sensitive organisms including some gram-negative bacilli important in bacterial endophthalmitis. When administered in combination with the renal enzyme inhibitor MK-791, plasma and aqueous concentrations of MK-787 were markedly potentiated, although vitreous concentrations were minimally affected. The potential usefulness of MK-787 in conjunction with MK-791 in the infected eye should be examined further in an animal model of bacterial endophthalmitis.