Selective Spectrofluorimetric Protocol for Determination of Commonly Used Gram-negative Bactericidal Drug in Combined Pharmaceutical Dosage Forms and Human Plasma

Gram-negative bacteria cause infections such as skin infection, meningitis, and pneumonia in human being. Gram-negative bacteria are highly resistant to most availaible bactericidal drugs. One of the most commonly used Gram-negative bactericidal drug is Polymyxin B sulfate (PMS). In addition, it is used in cases of highly resistant Gram-negative bacterial infections. The widespread of PMS necessitate the development of an exceedingly sensitive and selective fluorimetric assay for its determination in pure form, different pharmaceutical dosage forms, and human plasma. The presented method is used to determine PMS in their dosage form (vials) and combined pharmaceutical formulations (skin and eye ointments) with a high degree of accuracy and selectivity. The described procedure relies on the structure of a derivative of a high degree of fluorescence called dihydropyridine, via the condensation of the amino moiety of PMS with two equivalents of acetylacetone in the presence of formaldehyde and Teorell buffer (pH = 3). The fluorescent product was measured at 471 nm (λ_ex = 402 nm). The linearity ranged from 100-3000 ng mL^-1 of PMS with an excellent r² of 0.9998. LOD and LOQ were 27.16 ng mL^-1 and 82.30 ng mL^-1, respectively. Owing to the developed method's high selectivity, it was successfully utilized for assay of PMS, in the ointment, in the presence of oxytetracycline as an active ingredient. Furthermore, the procedure applied for the estimation of parenteral PMS in human plasma with very good mean recovery 97.42 ± 1.46.

Tarsocrural joint polymyxin B concentrations achieved following intravenous regional limb perfusion of the drug via a saphenous vein to healthy standing horses

OBJECTIVE

To determine whether therapeutic concentrations (> 0.5 to 1.0 μg/mL) of polymyxin B (PB) were achieved in the tarsocrural joint of horses when the drug was administered by IV regional limb perfusion (IV-RLP) via a saphenous vein at doses of 25, 50, and 300 mg and to describe any adverse systemic or local effects associated with such administration.

ANIMALS

9 healthy adult horses.

PROCEDURES

In the first of 2 experiments, 6 horses each received 25 and 50 mg of PB by IV-RLP via a saphenous vein with at least 2 weeks between treatments. For each treatment, a tourniquet was placed at the midmetatarsus and another was placed midway between the stifle joint and tarsus. Both tourniquets were removed 30 minutes after the assigned dose was administered. Blood and tarsocrural joint fluid samples were collected for determination of PB concentration before and at predetermined times after drug administration. In experiment 2, 4 horses were administered 300 mg of PB by IV-RLP in 1 randomly selected pelvic limb in a manner identical to that used in experiment 1.

RESULTS

For all 3 doses, the mean synovial fluid PB concentration was > 10 times the therapeutic concentration and below the level of quantification at 30 and 1,440 minutes after drug administration, respectively. No adverse systemic or local effects were observed following PB administration.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that IV-RLP of PB might be a viable alternative for treatment of horses with synovial infections caused by gram-negative bacteria.

Benchtop-fabricated lipid-based electrochemical sensing platform for the detection of membrane disrupting agents

There are increasing concerns about the danger that water-borne pathogens and pollutants pose to the public. Of particular importance are those that disrupt the plasma membrane, since loss of membrane integrity can lead to cell death. Currently, quantitative assays to detect membrane-disrupting (lytic) agents are done offsite, leading to long turnaround times and high costs, while existing colorimetric point-of-need solutions often sacrifice sensitivity. Thus, portable and highly sensitive solutions are needed to detect lytic agents for health and environmental monitoring. Here, a lipid-based electrochemical sensing platform is introduced to rapidly detect membrane-disrupting agents. The platform combines benchtop fabricated microstructured electrodes (MSEs) with lipid membranes. The sensing mechanism of the lipid-based platform relies on stacked lipid membranes serving as passivating layers that when disrupted generate electrochemical signals proportional to the membrane damage. The MSE topography, membrane casting and annealing conditions were optimized to yield the most reproducible and sensitive devices. We used the sensors to detect membrane-disrupting agents sodium dodecyl sulfate and Polymyxin-B within minutes and with limits of detection in the ppm regime. This study introduces a platform with potential for the integration of complex membranes on MSEs towards the goal of developing Membrane-on-Chip sensing devices.

Facile Generation of Biomimetic-Supported Lipid Bilayers on Conducting Polymer Surfaces for Membrane Biosensing

Membrane biosensors that can rapidly sense pathogen interaction and disrupting agents are needed to identify and screen new drugs to combat antibiotic resistance. Bioelectronic devices have the capability to read out both ionic and electrical signals, but their compatibility with biological membranes is somewhat limited. Supported lipid bilayers (SLBs) have served as useful biomimetics for a myriad of research topics involving biological membranes. However, SLBs are traditionally made on inert, rigid, inorganic surfaces. Here, we demonstrate a versatile and facile method for generating SLBs on a conducting polymer device using a solvent-assisted lipid bilayer (SALB) technique. We use this bioelectronic device to form both mammalian and bacterial membrane mimetics to sense the membrane interactions with a bacterial toxin (α-hemolysin) and an antibiotic compound (polymyxin B), respectively. Our results show that we can form high quality bilayers of both types and sense these particular interactions with them, discriminating between pore formation, in the case of α-hemolysin, and disruption of the bilayer, in the case of polymyxin B. The SALB formation method is compatible with many membrane compositions that will not form via common vesicle fusion methods and works well in microfluidic devices. This, combined with the massive parallelization possible for the fabrication of electronic devices, can lead to miniaturized multiplexed devices for rapid data acquisition necessary to identify antibiotic targets that specifically disrupt bacterial, but not mammalian membranes, or identify bacterial toxins that strongly interact with mammalian membranes.

Validation of an UV spectrophotometric assay for the quantification of polymyxin B in solid lipid nanoparticles

Polymyxins are efficient antibiotic drugs used for the treatment of Gram-negative bacterial infections. These compounds are not absorbed in the gastrointestinal tract and are responsible for serious toxicological effects. In order to enhance their therapeutic effectiveness, decrease the adverse/toxic side effects and promote a sustained release profile, a derivative--polymyxin B sulphate--has been formulated in solid lipid nanoparticles (SLNs) intended for buccal administration. To quantify polymyxin B in the formulation, UV spectrophotometry analysis was applied, validating the analytical methodology by assessing the selectivity, accuracy, precision, linearity, and repeatability. Analyses were performed at 210 nm keeping the samples at 25 degrees C. Results showed that lipid composition of SLNs did not interfere with the polymyxin B spectra. The linearity showed a correlation coefficient of 0.9977 in the range of 5-90 μg/mL. Quantification of polymyxin B by UV spectrophotometry, at 210 nm in SLN formulations, was approved in all analyzed parameters, validating the methodology proposed in this work.

Ex-vivoevaluation of alginate microparticles for Polymyxin B oral administration

A crosslinked alginate microparticle system for the targeting to the lymphatic system by Peyer's patches (PP) uptake was designed in order to improve the oral absorption of Polymyxin B (PMB). To verify mucoadhesion and PP uptake, microparticles labelled with fluorescein isothiocyanate (FITC) were prepared by spray-drying technique and crosslinking reactions with calcium ions and chitosan (CS), in vitro characterized and assayed by an ex vivo method. Microparticles showed a size less then 3 microm, an antibiotic loading level of 11.86 +/- 0.70%, w/w, a sustained drug release behaviour in simulated gastro-intestinal (GI) fluids and a preserved biological activity throughout the manufacture. The ex vivo study was performed by a perfusion method on intestinal tracts of just sacrificed adult rats. The recovered samples were analysed by epifluorescence microscope for mucoadhesion and PP uptake and by microbiological analysis for antibiotic activity preservation, providing evidence of mucoadhesion at the level of both PP and non-PP epithelium, uptake by PP and PMB microbiological activity in PP tissue. Furthermore, the study revealed the involvement of transport pathways across villous enterocytes.

Simultaneous determination of neomycin sulfate and polymyxin B sulfate by capillary electrophoresis with indirect UV detection

A simple and rapid capillary electrophoresis method, with indirect UV detection, for the simultaneous determination of neomycin sulfate and polymyxin B sulfate in pharmaceutical formulations was developed. Critical parameters such as pH, buffer composition and concentration, voltage and injection time have been studied to evaluate, how they affect responses, such as resolution and migration times. Separation was performed on a fused silica capillary with 50 microm i.d. and 27 cm total length at an applied voltage of 6 kV with a 15 mM phosphate run buffer (pH 5.0) containing 40 mM N-(4-hydroxy-phenyl)acetamide and 50 mM tetradecylammonium bromide (TTAB). The detection wavelength was set at 280 nm. Quantitative analysis was validated by testing the reproducibility of the method, giving a relative standard deviation less than 0.4 and 2.4% for the repeatability of migration time and corrected peak area, respectively. Accuracy was tested by spiking eye-ear formulations with standards and the recoveries of neomycin sulfate and polymyxin B sulfate were found to be between 97.44-103.18% and 96.85-101.68%, respectively. Linearity of neomycin sulfate and polymyxin B sulfate were obtained in the ranges of 17-682 and 24-608 microg/mL, respectively, with r(2) values above 0.999. The established TLC-densitometric method was applied to evaluate the proposed CE method, and comparable results were obtained by using CE with much shorter analysis time and a small quantity of solvents consumed. The developed method is also the first report on the simultaneous determination of neomycin sulfate and polymyxin B sulfate in pharmaceutical preparations by CE.

Determination of cell mass and polymyxin using multi-wavelength fluorescence

Multi-wavelength fluorescence was applied for on-line monitoring of cell mass and the antibiotic polymyxin B in Bacillus polymyxa cultivations. By varying the phosphate and nitrogen content of the medium different polymyxin-cell mass ratios could be obtained. Using this strategy, it was possible to investigate if multi-wavelength fluorescence is able to give independent prediction of the two parameters. Partial least square (PLS) regression was applied to establish mathematical relationships between off-line determined cell mass and polymyxin concentrations and on-line collected fluorescence data. For polymyxin one universal PLS model, with a correlation of 0.95 and a root mean square error of cross validation (RMSECV) of 35 mgl(-1), could be constructed. However, correlation between fluorescence and cell mass dry weight could not be established including data from all three types of cultivations. For data from each type of cultivation, separate models with high correlation and low RMSECV values were built. A large variation in cellular composition as a result of the different levels of nitrogen and phosphorus in the cultivations was the probable reason to the necessity of building three models. The results of the present investigation indicate that production of polymyxin is concomitantly regulated by phosphate and nitrogen as the highest polymyxin yield on cell mass, 0.17+/-0.01 gg(-1), was reached in the cultivations where both nitrogen and phosphate concentrations were kept low.

Identification and quantitation of polymyxin B, framycetin, and dexamethasone in an ointment by using thin-layer chromatography with densitometry

A new thin-layer chromatographic-densitometric method has been developed for rapid identification and quantitative determination of polymyxin B, framycetin, and dexamethasone in a dental ointment. Silica gel 60 and F254 silica gel 60 plates were used for separating antibiotics and dexamethasone acetate, respectively. When determining framycetin and polymyxin B, chromatograms were developed by using 2 mobile phases, namely methanol and methanol-n-butanol-ammonia (25%)-chloroform (14 + 4 + 9 + 12, v/v/v/v/). The densitometric measurements were made at 550 nm after detection with 0.3% ninhydrin solution. Dexamethasone was determined by using the mobile phase cyclohexane-ethyl acetate (2 + 3, v/v) and ultraviolet densitometric recording at 245 nm. The results obtained for individual constituents with the chromatographic-densitometric method demonstrate similar accuracy, relative standard deviation values from 1.49 to 2.47%, and relative error values from 0.02 to 0.81% and are comparable to those obtained with the reference methods.

Temperature dependence of the binding of endotoxins to the polycationic peptides polymyxin B and its nonapeptide

The interaction between endotoxins-free lipid A and various lipopolysaccharide (LPS) chemotypes with different sugar chain lengths-and the polycationic peptides polymyxin B and polymyxin nonapeptide has been investigated by isothermal titration calorimetry between 20 and 50 degrees C. The results show a strong dependence of the titration curves on the phase state of the endotoxins. In the gel phase (<30 degrees C for LPS and <45 degrees C for lipid A), an endothermic reaction is observed, for which the driving force is an entropically driven endotoxin-polymyxin interaction, due to disruption of the ordered water structure and cation assembly in the lipid A backbone and adjacent molecules. In the liquid crystalline phase (>35 degrees C for LPS and >47 degrees C for lipid A) an exothermic reaction takes place, which is mainly due to the strong electrostatic interaction of the polymyxins with the negative charges of the endotoxins, i.e., the entropic change DeltaS is much lower than in the gel phase. For endotoxins with short sugar chains (lipid A, LPS Re, LPS Rc) the stoichiometry of the polymyxin binding corresponds to pure charge neutralization; for the compounds with longer sugar chains (LPS Ra, LPS S-form) this is no longer valid. This can be related to the lower susceptibility of the corresponding bacterial strains to antibiotics.

Liquid chromatography–mass spectrometry study towards the pH and temperature-induced N-acyl migration in polymyxin B

In the course of the synthesis and purification of new polymyxins and analogues, formation of a by-product with identical mass was observed and it was believed that this might be the result of acyl migration from the Nalpha- to the Ngamma-position of residue alpha,-gamma-diaminobutyric acid 1 (Dab1) under acidic conditions. Therefore, a LC-MS/MS study was initiated to establish the stability of polymyxin B3 in aqueous solution at room temperature and 60 degrees C, as well as different pH values (i.e. 1.4, 4.4 and 7.4). It was shown that the by-product, which is actually formed in the course of the purification of polymyxin B3 after evaporation in acidic medium, has a retention time similar to Ngamma-polymyxin B3. Acyl-migration occurred most rapidly at 60 degrees C and pH 7.4. Furthermore, it was established that migration of the acyl from the Nalpha- to the Ngamma-position of residue Dab1 is reversible and that the equilibrium seems to be in favor of the Nalpha-acylated compound.

Development of a liquid chromatographic method for ear drops containing neomycin sulphate, polymyxin B sulphate and dexamethasone sodium phosphate

Two liquid chromatographic methods were developed to analyse ear drops containing neomycin sulphate, polymyxin B sulphate and dexamethasone sodium phosphate. This formulation will be described in the Belgian National Formulary. Since neomycin, an aminoglycoside antibiotic, has no UV chromophore and pre or post column derivatization is complicated, pulsed electrochemical detection on a gold electrode was chosen to determine neomycin. Polymyxin B sulphate and dexamethasone sodium phosphate do have a UV chromophore. So, a single LC method with UV detection was developed for the determination of polymyxin B sulphate and dexamethasone sodium phosphate. The sample pretreatment is simply done by diluting the formulation with water. For each method, the influence of the different chromatographic parameters on the separation, the interference of other active compounds and excipients, the repeatability and the linearity were investigated. Finally, the content of the actives in the formulation was studied at 0, 2, 4, 6, and 8 weeks.

[Study of biosensor technology on the detection of endotoxin-neutralizing materials]

OBJECTIVE

To explore the application of biosensor technology in the determination of endotoxin-neutralizing materials.

METHODS

After mixing polymyxin B (PMB) with endotoxin in certain concentration, the neutralizing ratio of PMB to endotoxin was assessed by biosensor technique and limulus amebocyte lysate test respectively. The results from the two methods were compared.

RESULTS

The neutralizing ratio of PMB to endotoxin as assessed by biosensor technology was 0.35 microg to 1 ng, while that by dynamic turbidimetric and chromogenic limulus amebocyte lysate (LAL) technique was 0.5 mg to 1 ng and 1 mg to 1 ng, respectively. The results obtained by biotechnology were similar to that by biosensor technique.

CONCLUSION

Biosensor technology was an accurate, convenient and rapid method for the determination of potency of endotoxin-neutralizing materials.

Determination of hydrocortisone, polymyxin B and Zn-bacitracin in pharmaceutical preparations by micellar electrokinetic chromatography

A new, simple and accurate micellar electrokinetic chromatography (MEKC) method is established for quantification of hydrocortisone, polymyxin B and Zn-bacitracin in local pharmaceutical preparations. The separation was carried out at 25 degrees C and 25 kV, using a 15 mmol L(-1) phosphate-15 mmol L(-1) borate buffer (pH 8.2), 60 mmol L(-1) sodium dodecylsulfate (SDS), and 10% methanol-water (v/v) as background electrolyte. Under these conditions the analysis takes about 23 min. The method has been applied for quantifying these compounds in two different commercial pharmaceutical products and the method gave good results when compared with a reference spectrophotometric multivariate calibration method.

Micellar electrokinetic capillary chromatography as an alternative method for the determination of dexamethasone, trimethoprim, and polymyxin B

A micellar electrokinetic capillary chromatographic method is presented which enables quantification of dexamethasone, polymyxin B and trimethoprim in synthetic mixtures and pharmaceutical products. Separation was carried out at 25 degrees C and 30 kV, with 10 mmol L(-1) borate-phosphate buffer adjusted to pH 8 as electrolyte, with 50 mmol L(-1) sodium dodecyl sulfate. Under these conditions separations were performed in 10 min. The limits of detection and quantification were approximately 2 mg L(-1) for each component, except for polymyxin B. The method was applied to different commercial formulations.

Simultaneous identification and quantitative determination of neomycin sulfate, polymixin B sulfate, zinc bacytracin and methyl and propyl hydroxybenzoates in ophthalmic ointment by TLC

A thin layer chromatographic-densitometric method for identification and quantitation of neomycin sulfate, polymixin B sulfate, zinc bacytracin and auxiliary substances (methyl and propyl hydroxybenzoates) in ophthalmic ointment was developed. To separate these constituents the silica gel coated TLC plates and two mobile phases were used. The suitable mobile phases were: methanol-n-butanol-ammonia 25%-chloroform (14:4:9:12, v/v/v/v) for determination of antibiotics and n-pentane-glacial acetic acid (66:9, v/v) for methyl and propyl hydroxybenzoates. The antibiotic chromatograms were detected by using ninhydrin ethanol solution, while densitometric measurements were made at lambda = 550 nm. Hydroxybenzoates were identified by UV measurements at lambda = 260 nm. The constituents under consideration were well separated at sufficient detection level. The recovery for all constituents ranged from 98.08% to 104.95%.

Analysis of polymyxin B sulfate by capillary zone electrophoresis with cyclodextrin as additive. Method development and validation

A capillary zone electrophoresis method for analysis of polymyxin B sulfate is described. In this method, triethanolamine (TEA)-phosphate buffer at pH 2.5 was employed to reduce the adsorption of analyte onto the capillary wall. Methyl-beta-cyclodextrin (M-beta-CD) and 2-propanol (IPA) were found to be necessary for selectivity enhancement. In order to optimize the method and to control its robustness, a central composite design was performed with four parameters, i.e. concentration of M-beta-CD, TEA, IPA and buffer pH. The optimal separation conditions were as follows: capillary, 55 cm (50 microm I.D., 47 cm effective length); 130 mM TEA-phosphate buffer (pH 2.5) containing 5 mM M-beta-CD and 5% IPA; 24 kV (51 microA) applied voltage; column temperature, 20 degrees C. Further, linearity and limits of detection quantification were examined. Three commercial samples were analyzed quantitatively.

Liquid chromatography of polymyxin B sulphate

A reversed-phase liquid chromatography method for analysis of polymyxin B sulphate is described. The method uses a YMC-Pack Pro, C18, 5 microm, 250x4.6 mm I.D. column maintained at 30 degrees C. The mobile phase comprises acetonitrile-sodium sulphate (0.7%, m/v)-phosphoric acid (6.8%, v/v dilution of 85%, m/m phosphoric acid)-water (22.25:50:5:22.75) at a flow-rate of 1.0 ml/min. Detection was by UV at 215 nm. The method is able to resolve polymyxin B1, the major component, from more than thirty other components present in the complex. Robustness was evaluated by performing a full-factorial design experiment. The method showed good selectivity, repeatability, linearity and sensitivity.

Analytical inverse supercritical fluid extraction of polar pharmaceutical compounds from cream and ointment matrices

It has been shown that inverse supercritical fluid extraction (SFE) can be used to analytically isolate a polar analyte from its matrix even at low concentrations (0.016%). Inverse SFE has been shown to be successful not only for the semi-solid Neosporin ointments, but also for the semi-liquid Neosporin creams as well. The technique has been shown to be superior to solid-phase extraction in both cases and affords the analytical chemist a quicker and safer method of sample preparation of analytes from both creams and ointments.

Flow microcalorimetric assay of antibiotics--II. Neomycin sulphate and its combinations with polymyxin B sulphate and zinc bacitracin on interaction with Bacillus pumilus (NCTC 8241)

A flow microcalorimetric assay for Neomycin has been developed which is monitored through interaction of the antibiotic with Bacillus pumilus as the test organism. The assay has better reproducibility (relative standard deviation 2.3%) and is more sensitive than conventional microbiological bioassay (0.5-2 micrograms ml-1). The effects of combinations with zinc bacitracin, with polymyxin B sulphate, and with both zinc bacitracin and polymyxin B sulphate (both in equimolar proportions), and in those proportions present in the commercial preparation TrisepR (ICI, Macclesfield, UK) have also been investigated. Synergy was observed for the combinations of Neomycin with the other two antibiotics in binary mixtures at the relative proportions found in TrisepR. The addition of all three antibiotics at the levels used in TrisepR did not show synergy. However, addition of all three antibiotics at equimolar concentrations did show synergy. It is suggested that microcalorimetry may be useful in in vitro experiments for exploring the relative proportions required for maximal effect in antibiotic combinations.

Flow microcalorimetric assay of antibiotics--III. Zinc bacitracin and its combinations with polymyxin B sulphate and neomycin sulphate on interaction with Micrococcus luteus

A flow microcalorimetric assay for zinc bacitracin has been developed which has better reproducibility (relative standard deviation less than 2%) and sensitivity (0.02 micrograms ml-1) than conventional microbiological assays, and requires an assay time of between 7.5-9 h. The assay is not suitable for zinc bacitracin determinations in the presence of equimolar concentrations of polymyxin B sulphate or neomycin sulphate, or of these antibiotics in the proportions in which they occur in the commercial preparation Trisep (ICI, Macclesfield, UK).

Flow microcalorimetric assay of antibiotics--IV. Polymyxin B sulphate, neomycin sulphate, zinc bacitracin and their combinations with Escherichia coli suspended in buffer plus glucose medium

Flow microcalorimetric assays for polymyxin B sulphate and neomycin sulphate have been developed using Escherichia coli as the test organism, suspended in a glucose plus buffer medium. These assays have a better reproducibility (relative standard deviations 3.2 and 2.0%, respectively), and require a shorter time (1 h including time required for preparation of the calorimeter) than do conventional microbiological assays, but are not as sensitive. It is suggested that a screening programme might produce a small group of more suitable (i.e. more sensitive) test organisms, which could be used to develop rapid and reproducible flow microcalorimetric assays for a wide range of antibiotics by the procedure described. The effect of combinations of polymyxin B sulphate, neomycin sulphate and zinc bacitracin (the antibiotic components of the commercial preparation Trisep, ICI, Macclesfield, UK) on the power output of cells suspended in glucose plus buffer medium is also reported. In defined combinations, the effects of neomycin sulphate appeared to be exerted before those of polymyxin B sulphate.

Flow microcalorimetric assay of antibiotics--I. Polymyxin B sulphate and its combinations with neomycin sulphate and zinc bacitracin on interaction with Bordetella bronchiseptica (NCTC 8344)

A flow microcalorimetric assay for polymyxin B sulphate has been developed which has a better reproducibility (relative standard deviation less than 3%) and sensitivity (0.35 micrograms ml-1) than conventional microbiological assays, and requires an assay time of ca. 4.5 h. The combinations with zinc bacitracin, with neomycin sulphate, and with both zinc bacitracin and neomycin sulphate indicate antagonism between these antibiotics upon interaction with Bordetella bronchiseptica (NCTC 8344). The combinations of all three antibiotics assayed were: (1) equimolar proportions; and (2) those proportions present in the commercial preparation TrisepR (ICI, Macclesfield, UK).

[Structural-functional research on polymyxins. 1H-NMR spectra of polymyxin B and its shortened analog]

Polymyxin B and its shortened analog were studied comparatively by 1H-NMR spectroscopy. Analysis of the signal chemical shifts, constants of spin-spin interaction of 3J HN-C alpha H and temperature coefficients of the NH signal chemical shifts revealed absolute structural identity of both molecules cyclic parts. This proved that there was no conformative interaction between the cyclic and linear parts of the polymyxin B molecule. Comparison of the results with the data on the biological activity showed that the hydrophobic N-end moiety of the polymyxin B molecule played a specific role in its antibacterial effect and toxicity.

Selective decontamination and the anaerobic faecal flora

Selective decontamination with non-absorbable antibiotics of the gastrointestinal tract of patients with impaired host defense is increasingly applied to prevent infections with gram-negative facultatively anaerobic rods. In vivo experiments on the effect of antibiotics on the human intestinal flora were performed with (ex-germ-free) mice. The experiments have shown that the human obligately anaerobic flora did not change during selective decontamination with polymyxin B, but Enterobacteriaceae were eliminated. The magnitude of differences between the sensitivity to antibiotics of the human obligately anaerobic flora and the Enterobacteriaceae in vitro may be used as an index for the usefulness of the antibiotic for selective decontamination. Binding of the antibiotics to intestinal contents has been found to be important for the estimation of the daily dose. The release of the bound antibiotic could contribute to the maintenance of equable concentrations in the intestine.

A study of the structure and dynamics of complexes between polymyxin B and phosphatidylglycerol in monolayers by fluorescence

Interactions between the antibiotic polymyxin B and monolayers of dipalmitoylglycerophosphoglycerol have been reinvestigated through a study of the structure and dynamics of the complexes by means of an interface fluorimeter of our fabrication. A fluorescence technique has been developed where the use of linearly polarized incident beams gives the simultaneous determination of the orientation and the lateral diffusion rate of a fluorescent probe inserted in the film. The present investigation was carried out with 12-(9-anthroyloxy)-stearic acid, a fluorescent compound which forms non-fluorescent photodimers upon illumination. Orientation of the probe was studied by computing the ratio of the two dimerization constants KD and the ratio of the fluorescence intensities obtained with crossed linearly polarized incident lights. The lateral diffusion rate of the probe was obtained by measuring fluorescence recovery after photobleaching (photodimerization) of the probe. Control experiments, carried out with dimyristoylglycerophosphocholine, a lipid which does not interact with polymyxin B, show that the antibiotic does not significantly modify the behaviour of the probe. Both in terms of orientation and dynamics, with respect to dipalmitoylglycerophosphoglycerol, when the antibiotic is present in the subphase (1 microM, saturating conditions), data indicate that the lipid remains in a liquid-expanded state. This is true even at a high surface pressure (pi approximately equal to 37 mN X m-1), above the apparent 'transition' which can be observed at 30-35 mN X m-1 on its compression isotherm. Computation of the contribution of polymyxin B to the film expansion to the conclusion that this 'transition' would be a structural transition between two models of interaction: one, below the 'transition', where the polypeptide ring penetrates between the film-forming lipid molecules and another one, above the 'transition', were the antibiotic is adsorbed at the lipid-water interface with only its hydrocarbon chain penetrating the film.

High-performance liquid chromatographic analysis of neomycin in petrolatum-based ointments and in veterinary formulations

A high-performance liquid chromatographic (HPLC) method has been developed for the assay of neomycin in petrolatum-based ophthalmic and topical ointments and in veterinary formulations. Neomycin assay interferences from drugs, such as bacitracin and polymyxin B and inactive components, e.g. wax, were eliminated by a methanol wash and/or a partitioning method. The extracted neomycin was derivatized with 2,4-dinitrofluorobenzene followed by normal-phase HPLC with detection at 254 nm. The average recovery of neomycin from spiked samples was approximately 100% with a relative standard deviation of less than 1%.

Isolation and characterization of three new polymyxins in polymyxins B and E by high-performance liquid chromatography

Two polymyxin antibiotics, polymyxins B and E (colistin), have been separated analytically into ten to thirteen components on a commercial reversed-phase material by isocratic elution with a mixture of acetonitrile, phosphate/formate and acetate buffer containing sodium sulphate and triethylamine. The analytical system was transferred to a preparative system, using a C18-bonded stationary phase, without extensive impairing of the selectivity. The major components of each product were isolated and characterized by high-performance liquid chromatography, amino acid analysis and identification of the fatty acid. Three components were isolated and characterized for the first time. The fatty acid was also identified in some of the minor components.