Daily fluid intake as a novel covariate affecting the population pharmacokinetics of polymyxin B in patients with sepsis

BACKGROUND

Polymyxin B dosing in patients with sepsis is difficult because pathophysiological changes and supportive therapies alter drug pharmacokinetics (PK). This study aimed to investigate the impact of fluid management and renal function on the PK of polymyxin B and to propose alternative dosing regimens.

METHODS

Patients (aged ≥ 18 y) with sepsis and receiving intravenous polymyxin B for ≥ 96 h were enrolled. Blood samples were collected at steady state. Plasma concentrations were measured by liquid chromatography-tandem mass spectrometry and subjected to population PK modelling. Monte Carlo simulations were used to optimise dosage regimens.

RESULTS

Eighty-three patients with a median (range) daily fluid intake of 4.2 (1.3-8.4) L and a creatinine clearance (CrCL) of 87.5 (17.3-309.7) mL/min were included. Polymyxin B PK was adequately characterised by a two-compartment model. The PK covariate analysis revealed daily fluid intake statistically significantly affected central volume of distribution and central compartment clearance (CL), and CrCL influenced CL. Simulation indicated that a decreased dosing would be suitable for patients with renal dysfunction (CrCL < 40 mL/min), and therapeutic drug monitoring is recommended to avoid exposure fluctuation when patients have fluid overload.

CONCLUSIONS

Fluid management as well as renal function are essential factors affecting polymyxin B PK for patients with sepsis, which can help optimise dosage regimens.

Synergy of polymyxin B and minocycline against KPC-3- and OXA-48-producing Klebsiella pneumoniae in dynamic time-kill experiments: agreement with in silico predictions

OBJECTIVES

Combination therapy is often used for carbapenem-resistant Gram-negative bacteria. We previously demonstrated synergy of polymyxin B and minocycline against carbapenem-resistant Klebsiella pneumoniae in static time-kill experiments and developed an in silico pharmacokinetic/pharmacodynamic (PK/PD) model. The present study assessed the synergistic potential of this antibiotic combination in dynamic experiments.

METHODS

Two clinical K. pneumoniae isolates producing KPC-3 and OXA-48 (polymyxin B MICs 0.5 and 8 mg/L, and minocycline MICs 1 and 8 mg/L, respectively) were included. Activities of the single drugs and the combination were assessed in 72 h dynamic time-kill experiments mimicking patient pharmacokinetics. Population analysis was performed every 12 h using plates containing antibiotics at 4× and 8× MIC. WGS was applied to reveal resistance genes and mutations.

RESULTS

The combination showed synergistic and bactericidal effects against the KPC-3-producing strain from 12 h onwards. Subpopulations with decreased susceptibility to polymyxin B were frequently detected after single-drug exposures but not with the combination. Against the OXA-48-producing strain, synergy was observed between 4 and 8 h and was followed by regrowth. Subpopulations with decreased susceptibility to polymyxin B and minocycline were detected throughout experiments. For both strains, the observed antibacterial activities showed overall agreement with the in silico predictions.

CONCLUSIONS

Polymyxin B and minocycline in combination showed synergistic effects, mainly against the KPC-3-producing K. pneumoniae. The agreement between the experimental results and in silico predictions supports the use of PK/PD models based on static time-kill data to predict the activity of antibiotic combinations at dynamic drug concentrations.

Population pharmacokinetics of polymyxin B in patients with liver dysfunction

AIMS

Polymyxin B (PMB) is widely used to treat infections caused by multidrug-resistant Gram-negative pathogens. Currently, the pharmacokinetic data of PMB in patients with liver dysfunction are limited. This study aimed to develop a population pharmacokinetic (PopPK) model of PMB in patients with liver dysfunction and identify the factors affecting PMB pharmacokinetics.

METHODS

We conducted a retrospective pharmacokinetic study involving 136 adults with different levels of liver function. Nonlinear mixed effects modelling was used to develop a PopPK model of PMB. Monte Carlo simulation was used to design PMB dosage schedules across various liver and renal functions.

RESULTS

PMB pharmacokinetic analyses included 401 steady-state concentrations in 136 adult patients. A one-compartment pharmacokinetic model with first-order absorption and elimination was used to describe the data. The typical population value of PMB clearance was 2.43 L/h and the volume of distribution was 23.11 L. This study revealed that creatinine clearance (CrCL) and Child-Pugh class were significantly associated with PMB pharmacokinetic parameters; however, clinically relevant variations of dose-normalized drug exposure were not significant. For patients with a minimum inhibitory concentration of ≤0.5 mg/L, the appropriate dose was 40-75 mg/12-h. When the dose exceeded 100 mg/12-h, the risk of nephrotoxicity increased significantly.

CONCLUSIONS

This study provided PMB pharmacokinetic information for patients with liver dysfunction. Patients with renal and liver dysfunctions may not require an initial dose adjustment. Rather than PopPK-guided dose adjustment, therapeutic drug monitoring of PMB plays a more direct role in optimizing dosing regimens based on its therapeutic window.

Individual Components of Polymyxin B Modeled via Population Pharmacokinetics to Design Humanized Dosage Regimens for a Bloodstream and Lung Infection Model in Immune-Competent Mice

Polymyxin B is a "last-line-of-defense" antibiotic approved in the 1960s. However, the population pharmacokinetics (PK) of its four main components has not been reported in infected mice. We aimed to determine the PK of polymyxin B1, B1-Ile, B2, and B3 in a murine bloodstream and lung infection model of Acinetobacter baumannii and develop humanized dosage regimens. A linear 1-compartment model, plus an epithelial lining fluid (ELF) compartment for the lung model, best described the PK. Clearance and volume of distribution were similar among the four components. The bioavailability fractions were 72.6% for polymyxin B1, 12.0% for B1-Ile, 11.5% for B2, and 3.81% for B3 for the lung model and were similar for the bloodstream model. While the volume of distribution was comparable between both models (17.3 mL for the lung and ~27 mL for the bloodstream model), clearance was considerably smaller for the lung (2.85 mL/h) compared to that of the bloodstream model (5.59 mL/h). The total drug exposure (AUC) in ELF was high due to the saturable binding of polymyxin B presumably to bacterial lipopolysaccharides. However, the modeled unbound AUC in ELF was ~16.7% compared to the total drug AUC in plasma. The long elimination half-life (~4 h) of polymyxin B enabled humanized dosage regimens with every 12 h dosing in mice. Daily doses that optimally matched the range of drug concentrations observed in patients were 21 mg/kg for the bloodstream and 13 mg/kg for the lung model. These dosage regimens and population PK models support translational studies for polymyxin B at clinically relevant drug exposures.

Polymyxin B Combined with Minocycline: A Potentially Effective Combination against blaOXA-23-harboring CRAB in In Vitro PK/PD Model

Polymyxin-based combination therapy is commonly used to treat carbapenem-resistant Acinetobacter baumannii (CRAB) infections. In the present study, the bactericidal effect of polymyxin B and minocycline combination was tested in three CRAB strains containing bla_OXA-23 by the checkerboard assay and in vitro dynamic pharmacokinetics/pharmacodynamics (PK/PD) model. The combination showed synergistic or partial synergistic effect (fractional inhibitory concentration index ≤0.56) on the tested strains in checkboard assays. The antibacterial activity was enhanced in the combination group compared with either monotherapy in in vitro PK/PD model. The combination regimen (simultaneous infusion of 0.75 mg/kg polymyxin B and 100 mg minocycline via 2 h infusion) reduced bacterial colony counts by 0.9–3.5 log₁₀ colony forming units per milliliter (CFU/mL) compared with either drug alone at 24 h. In conclusion, 0.75 mg/kg polymyxin B combined with 100 mg minocycline via 2 h infusion could be a promising treatment option for CRAB bloodstream infections.

External evaluation of published population pharmacokinetic models of polymyxin B

OBJECTIVES

Several population pharmacokinetics (popPK) models for polymyxin B have been constructed to optimize therapeutic regimens. However, their predictive performance remains unclear when extrapolated to different clinical centers. Therefore, this study aimed to evaluate the predictive ability of polymyxin B popPK models.

METHODS

A literature search was conducted, and the predictive performance was determined for each selected model using an independent dataset of 20 patients (92 concentrations) from the Third Xiangya Hospital. Prediction- and simulation-based diagnostics were used to evaluate model predictability. The influence of prior information was assessed using Bayesian forecasting.

RESULTS

Eight published studies were evaluated. In prediction-based diagnostics, the prediction error within ± 30% was over 50% in two models. In simulation-based diagnostics, the prediction- and variability-corrected visual predictive check (pvcVPC) showed satisfactory predictivity in three models, while the normalized prediction distribution error (NPDE) tests indicated model misspecification in all models. Bayesian forecasting demonstrated a substantially improvement in the model predictability even with one prior observation.

CONCLUSION

Not all published models were satisfactory in prediction- and simulation-based diagnostics; however, Bayesian forecasting improved the predictability considerably with priors, which can be applied to guide polymyxin B dosing recommendations and adjustments for clinicians.

Evaluation of Dose-Fractionated Polymyxin B on Acute Kidney Injury Using a Translational In Vivo Rat Model

We investigated dose-fractionated polymyxin B (PB) on acute kidney injury (AKI). PB at 12 mg of drug/kg of body weight per day (once, twice, and thrice daily) was administered in rats over 72 h. The thrice-daily group demonstrated the highest KIM-1 increase (P = 0.018) versus that of the controls (P = 0.99) and histopathological damage (P = 0.013). A three-compartment model best described the data (bias, 0.129 mg/liter; imprecision, 0.729 mg2/liter2; R2, 0.652,). Area under the concentration-time curve at 24 h (AUC24) values were similar (P = 0.87). The thrice-daily dosing scheme resulted in the most PB-associated AKI in a rat model.

Pharmacokinetics of the Individual Major Components of Polymyxin B and Colistin in Rats

The pharmacokinetics of polymyxin B₁, polymyxin B₂, colistin A, and colistin B were investigated in a rat model following intravenous administration (0.8 mg/kg) of each individual component. Plasma and urine concentrations were determined by LC-MS/MS, and plasma protein binding was measured by ultracentrifugation. Total and unbound pharmacokinetic parameters for each component were calculated using noncompartmental analysis. All of the polymyxin components had a similar clearance, volume of distribution, elimination half-life, and urinary recovery. The area under the concentration-time curve for polymyxins B₁ and B₂ was greater than those of colistins A and B. Colistin A (56.6 ± 9.25%) and colistin B (41.7 ± 12.4%) displayed lower plasma protein binding in rat plasma compared to polymyxin B₁ (82.3 ± 4.30%) and polymyxin B₂ (68.4 ± 3.50%). These differences in plasma protein binding potentially equate to significant differences in unbound pharmacokinetics, highlighting the need for more stringent standardization of the composition of commercial products currently available for clinical use.

Polymyxin B Nephrotoxicity: From Organ to Cell Damage

Polymyxins have a long history of dose-limiting toxicity, but the underlying mechanism of polymyxin B-induced nephrotoxicity is unclear. This study investigated the link between the nephrotoxic effects of polymyxin B on renal metabolic functions and mitochondrial morphology in rats and on the structural integrity of LLC-PK1 cells. Fifteen Wistar rats were divided into two groups: Saline group, rats received 3 mL/kg of 0.9% NaCl intraperitoneally (i.p.) once a day for 5 days; Polymyxin B group, rats received 4 mg/kg/day of polymyxin B i.p. once a day for 5 days. Renal function, renal hemodynamics, oxidative stress, mitochondrial injury and histological characteristics were assessed. Cell membrane damage was evaluated via lactate dehydrogenase and nitric oxide levels, cell viability, and apoptosis in cells exposed to 12.5 μM, 75 μM and 375 μM polymyxin B. Polymyxin B was immunolocated using Lissamine rhodamine-polymyxin B in LLC-PK1 cells. Polymyxin B administration in rats reduced creatinine clearance and increased renal vascular resistance and oxidative damage. Mitochondrial damage was confirmed by electron microscopy and cytosolic localization of cytochrome c. Histological analysis revealed tubular dilatation and necrosis in the renal cortex. The reduction in cell viability and the increase in apoptosis, lactate dehydrogenase levels and nitric oxide levels confirmed the cytotoxicity of polymyxin B. The incubation of LLC-PK1 cells resulted in mitochondrial localization of polymyxin B. This study demonstrates that polymyxin B nephrotoxicity is characterized by mitochondrial dysfunction and free radical generation in both LLC-PK1 cells and rat kidneys. These data also provide support for clinical studies on the side effects of polymyxin B.

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.

Alginate microparticles for Polymyxin B Peyer's patches uptake: microparticles for antibiotic oral administration

Microparticles with size less than 3 microm, able to be taken up by M cell of Peyer's patches for the drug delivery to the Gut Associated Limphoid Tissue (GALT), were developed in order to improve oral bioavailability of Polymyxin B (PMB). Less than 3 microm alginate microparticles resistant to gastro-intestinal media were prepared by spray-drying technique and cross-linking by calcium ions and chitosan. The cross-linked microparticles were evaluated for PMB content by spectrophotometric method, alginate/PMB interaction by rheological study, cross-linking degree by EDS analysis and PMB activity by microbiological assay. By modulating the polymer cross-linking degree, cationic PMB interacted on alginate chains leading to a proper PMB loading as well as antibiotic retention in gastric environment and sustained delivery in intestinal fluid. Moreover, the procedure resulted suitable for PMB biological activity preservation.

Polymyxin B for the treatment of multidrug-resistant pathogens: a critical review

Polymyxins have re-emerged in clinical practice owing to the dry antibiotic development pipeline and worldwide increasing prevalence of nosocomial infections caused by multidrug-resistant (MDR) Gram-negative bacteria. Polymyxin B and colistin (polymyxin E) have been ultimately considered as the last-resort treatment of such infections. Microbiological, pharmacokinetic, pharmacodynamic and clinical data available for polymyxin B are reviewed in this paper. Polymyxin B has rapid in vitro bactericidal activity against major MDR Gram-negative bacteria, such as Pseudomonas aeruginosa, Acinetobacter baumannii and Klebsiella pneumoniae. Acquired resistance to this agent is still rare among these pathogens. However, optimized dosage regimens are not known yet. Good clinical outcomes have been observed in the majority of the patients treated with intravenous polymyxin B in recent studies. However, these studies failed to provide definitive conclusions due to limitations of study design and additional clinical trials are required. Although combination therapy may be an attractive option based on some currently available in vitro data, clinical data supporting such recommendations are lacking. Since polymyxins will be increasingly used for the treatment of infections caused by MDR bacteria, clinical pharmacokinetic, pharmacodynamic and toxicodynamic studies underpinning the optimal use of these drugs are urgently required.

Immunomodulation by non-absorbable antibiotics given by the intragastric route

To test the role of bacterial fractions released from intestinal flora during immunomodulation by antimicrobial agents, BALB/c mice were treated with the non-absorbable antibiotics polymyxin B or teicoplanin by the intragastric route. The composition of faecal microbiota and the capacity of spleen cells to proliferate in response to B-cell and T-cell mitogens were assessed at several times during the treatment. Both antibiotics lowered the count of some bacteria of the intestinal flora and induced significant modifications in spleen cell ability to proliferate in response to mitogens. Thus, the active fractions released from intestinal bacteria during antibiotic treatments may be able to induce immunomodulating effects.

Transscleral Permeability of Fluorescent-Labeled Antibiotics

PURPOSE

To determine the in vitro transscleral permeability of antibiotics for posterior segment infection.

METHODS

Scleral sections from moist chamber-stored human globes were mounted in a 2-compartment perfusion chamber. Fluorescent-labeled vancomycin, polymyxin B, or penicillin G was added to the episcleral surface, while the choroidal side was slowly perfused with balanced salt solution (Alcon Laboratories, Inc., Ft. Worth, TX). The perfusate was collected and fluorescence was measured using a fluorometer. From the measurements, permeability (Ktrans) was calculated. Photomicrographs were taken with a fluorescent microscope to evaluate tissue absorption.

RESULTS

The Ktrans values (cm/s, mean +/- standard error) were 6.66 +/- 1.46 x 10(-7) for vancomycin, 3.90 +/- 0.59 x 10(-7) for polymyxin B, and 1.89 +/- 0.21 x 10(-6) for penicillin G. The percent of antibiotic that diffused across the sclera from the donor chamber in 24 hours was 20.6 +/- 4.2 for vancomycin, 12.6 +/- 2.0% for polymyxin B, and 50.8 +/- 4.8% for penicillin G.

CONCLUSIONS

This study shows that human sclera is more permeable to lower molecular weight, water-soluble penicillin G than to vancomycin or polymyxin B. The data suggests that a local, noninvasive, transscleral drug-delivery method may be reasonable for treating intraocular infections.

Natural medicaments in endodontics -- a comparative study of the anti-inflammatory action

The objective of this study was to evaluate the irritant potential of propolis, Casearia sylvestris, Otosporin and saline solution (control). Twenty-eight male Wistar rats were selected, anesthetized and four experimental sites were designed on their backs. Injections of 2% Evans blue were intravenously administered in the lateral caudal vein and 0.1 ml of the tested solutions was injected intradermally into the experimental sites. The animals were killed 1/2, 1, 3 and 6 hours after the injection of the solutions. Each piece of skin containing the lesion was immersed in formamide and incubated at 45 masculine C for 72 h. After filtration, optical density was measured in a spectrophotometer. Data were statistically analyzed by a 2-way non-parametric test. The highest values of extracted dye were observed at 3 hours characterizing a peak in the inflammatory process. Propolis was the least irritant solution. The natural medicaments tested in this study may be a valuable alternative for endodontic treatment.

In vitro evaluation of nebulization properties, antimicrobial activity, and regional airway surface liquid concentration of liposomal polymyxin B sulfate

PURPOSE

To manipulate the activity of polymyxin B sulfate (PXB sulfate) by encapsulation in liposomes derived from appropriately selected surfactants that exhibit optimum entrapment and aerosol delivery of encapsulated PXB sulfate.

METHODS

A combination of phospholipid (DMPG) and nonionic surfactants (Span 20 + Tween 80) was selected to encapsulate PXB sulfate. The nebulization properties were evaluated by nebulizing the liposomal dispersions with Pari LC Star nebulizers. The in vitro antibacterial activities of the original and nebulized liposomal formulations were evaluated against Pseudomonas aeruginosa (ATCC 27853) strains by broth microdilution. and their minimum inhibitory concentrations (MICs) were compared with those of free PXB sulfate and colistin methanesulfonate. Measurements of the aerosol properties during nebulization were used as input for a mathematical model of airway surface liquid in the lung of an average adult, to estimate the airway surface liquid concentration of the deposited liposomal PXB sulfate.

RESULTS

The selected combination of surfactants showed maximum nebulization efficiency without compromising liposomal integrity during nebulization. PXB sulfate was added at a concentration of 10 mg/ml, and a molar ratio of PXB sulfate to dimyristoyl phosphatidylglycerol (DMPG) (sodium salt) of 1:5 was required to achieve 100% entrapment of PXB sulfate and no leakage on nebulization. Another formulation comprising half the concentrations of the optimized non-ionic surfactants and DMPG was prepared to achieve a balance between the toxicity and efficacy after nebulization of encapsulated PXB sulfate. The in vitro antibacterial activities against Pseudomonas aeruginosa indicated that the activity of PXB sulfate could be manipulated by appropriate concentrations of the selected surfactants to achieve activity equivalent to that of colistin methanesulfonate, which is known to be less toxic than unencapsulated PXB sulfate. The estimated airway surface liquid concentrations of the deposited liposomal PXB sulfate reveal that the MIC of the nebulized liposomal PXB sulfate can be achieved over most of the tracheobronchial region, using a jet nebulizer with a volume fill of 2.5 ml or more.

CONCLUSION

It was established from this study that the encapsulation of PXB sulfate in liposomes reduces its activity against P. aeruginosa strains. Concentrations of PXB sulfate deposited in the tracheobroncial region, predicted using a mathematical model, were above the measured MICs except in the case of very high mucus production rate and low mucus velocities.

Antibacterial properties of cationic steroid antibiotics

Cationic steroid antibiotics have been developed that display broad-spectrum antibacterial activity. These compounds are comprised of steroids appended with amine groups arranged to yield facially amphiphilic morphology. Examples of these antibiotics are highly bactericidal, while related compounds effectively permeabilize the outer membranes of Gram-negative bacteria sensitizing these organisms to hydrophobic antibiotics. Cationic steroid antibiotics exhibit various levels of eukaryote vs. prokaryote cell selectivity, and cell selectivity can be increased via charge recognition of prokaryotic cells. Studies of the mechanism of action of these antibiotics suggest that they share mechanistic aspects with cationic peptide antibiotics.

Enhanced activity of liposomal polymyxin B against Pseudomonas aeruginosa in a rat model of lung infection

The bactericidal effectiveness of liposomal polymyxin B against Pseudomonas aeruginosa was investigated in an animal model of pulmonary infection. Polymyxin B was incorporated into liposomes composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and cholesterol (Chol) (2:1). Lung infection was induced in rats following intratracheal instillation of 10(7) colony-forming units (CFU) of P. aeruginosa (ATCC 27853) embedded in agar beads. Starting on day 3 post-infection, animals were treated daily, for 3 consecutive days, with saline, empty liposomes, free polymyxin B, or liposomal polymyxin B (2mg polymyxin B/kg body weight) by intratracheal instillation; animals were killed 24hr after the third drug instillation. Treatment of infected animals with liposomal polymyxin B significantly reduced the pulmonary bacterial counts (3.7+/-0.4log CFU/paired lungs) as compared with that of free polymyxin B (5.1+/-0.2log CFU/paired lungs). Treatment of infected animals with empty liposomes gave pulmonary bacterial counts similar to those obtained from the saline-treated group. Pulmonary infection with P. aeruginosa also resulted in lung injury as evidenced by increases in wet lung weight and decreases in angiotensin converting enzyme activity as well as increases in myeloperoxidase activity, an index of the inflammatory response. Treatment with free polymyxin B ameliorated the lung injuries induced by the microorganism, a protective effect that was more pronounced in the liposomal polymyxin B-treated group. The levels of polymyxin B in the lungs of the infected animals treated with the liposomal suspension were significantly higher (42.8+/-6.2 microg/paired lungs) compared with those treated with the free drug (8.2+/-0.4 microg/paired lungs). These data suggest that direct delivery of liposomal polymyxin B to the lung can be effective in the treatment of pulmonary infection with P. aeruginosa by enhancing retention of the antibiotic in the lung.

Tympanostomy tubes and otic suspensions: do they reach the middle ear space?

The treatment of patients with tympanostomy tubes (TTs) and otorrhea with medicated otic suspensions is well known, but confirmation of penetration into the middle ear is difficult. To address this question, we created an in vitro model of the human head and ear and then tested it with 5 different types of liquid exposure: tap water, soapy water, polymyxin B sulfate (Cortisporin), tobramycin and dexamethasone (TobraDex), and ciprofloxacin (Cipro) suspensions. A positive test result corresponded to liquids entering the middle ear through the TT. No positive test result was elicited with tap water (0/20), but soapy water did enter the middle ear (10/40) and was statistically significant (P = 0.0112). Without the use of slight tragal pressure, Cortisporin, TobraDex, and Cipro drops did not consistently pass through the TT (0/20, 1/25, 1/25). By placing the drops with the addition of tragal pressure, a statistically significant difference was obtained for each solution (20/20, 20/20, and 20/20, respectively [P < 0.0001]). We conclude that with a clean external auditory canal, patent TT, and no middle ear fluid, medicated otic suspensions enter the middle ear only when combined with slight tragal pressure.

A highly sensitive ELISA for the quantification of polymyxin B sulfate in human serum

A highly sensitive ELISA for the determination of polymyxin B sulfate (PMB) was developed which is capable of measuring as low as 32 pg/ml. Anti-PMB antibody was obtained by immunizing rabbits with PMB conjugated with mercaptosuccinyl bovine serum albumin (MS. BSA) using N-(gamma-maleimidobutyryloxy) succinimide (GMBS) as a heterobifunctional coupling agent. An enzyme marker was similarly prepared by coupling PMB with horseradish peroxidase (HRP) employing GMBS. This ELISA showed very low reactivity with the PMB analogue, polymyxin E (0.05%). The values for PMB concentration detected by this assay were comparable with those detected by the bioassay. Moreover, the ELISA was about 10,000 times more sensitive in detecting PMB at lower concentrations. Serum PMB concentration after the oral administration of a PMB tablet to human subjects was determined by the ELISA. PMB was rapidly absorbed from the gastrointestinal tract after the administration, then slowly decreased. These results indicate that the ELISA may be a valuable tool for studies of the pharmacokinetics and pharmacodynamics of the anti-endotoxin drug, PMB.

Biological activities of sustained polymyxin B release from calcium phosphate biomaterial prepared by dynamic compaction: an in vitro study

Calcium phosphate ceramics (CaP) have recently been proposed as a potential matrix for a bioactive drug delivery system (DDS) in which the effect in situ of a released therapeutic agent is favored by the biocompatibility, osteoconductivity, and bioresorption of the ceramic material. Polymyxin B (PMB) is a polypeptidic antibiotic which undergoes thermodamage above 60 degrees C. The dynamic compaction method was developed to consolidate the drug load on CaP powder without external heating. Two projectile velocities (50 and 25 m/s) were used here to achieve powder consolidation. Among the different techniques used to associate therapeutic agents with CaP, wet adsorption was performed before the dynamic compaction process. The PMB release profile was measured by a capillary electrophoresis technique, CaP crystallography was studied by x-ray diffraction, and CaP physicochemical analysis was performed by infrared spectroscopy. The biological activities of PMB-loaded compacted CaP were determined by the effect of the antibiotic and monocyte/macrophage degradation on compact surfaces. PMB release began after 2-3 days of incubation for blocks compacted at 25 m/s velocity and on day 5 for those compacted at 50 m/s velocity. A discrepancy was noted between the amounts of PMB released (0.5-2.1 mg) and the amounts initially compacted (2-8 mg) with CaP powder. The biological activities (antibacterial activity and inhibited lipopolysaccharide effects on monocyte/macrophage CaP degradation) of PMB released from compacted calcium-deficient apatite were unaltered. Thus, dynamic compaction allows PMB to be used with CaP ceramics without any loss in its integrity and biological effects.

Analysis of the intranasal distribution of ointment

OBJECTIVE

The use of intranasal ointment sniffed into the nasal cavity is widely recommended as a method to lubricate the nose and to prevent drying and crusting of the nasal mucosa and secretions. This therapy is often prescribed to patients with problems with minor episodes of epistaxis, after nasal packing has been removed, and in patients complaining of excessive dryness or crusting within the nose. Various preparations have been used for this purpose. At our institution Polysporin ointment is one of the commonly used preparations. This study evaluated the distribution of Polysporin ointment within the nasal cavities of subjects with no symptoms related to the nasal cavity.

CONCLUSIONS

The results of the study raise doubts about the effectiveness of this therapy.

Polymyxin B: pharmacokinetics of single doses given intravenously and intramuscularly to turkeys, and minimal inhibitory concentrations for Escherichia coli and Pasteurella multocida

The 50% and 90% minimal inhibitory concentrations (MIC50 and MIC90) of polymyxin B for avian Escherichia coli and Pasteurella multocida isolates were determined by the agar plate dilution method. Polymyxin B at approximate MIC level in serum was bactericidal for E. coli in 2 to 4 hours. Aqueous polymyxin B sulfate was administered by a single bolus intravenous injection into turkeys at 10,000 IU/kg, and by a single bolus intramuscular injection at 5,000, 10,000 or 20,000 IU/kg. Effective serum drug concentrations after intramuscular injection (MIC50 levels or greater) were maintained for E. coli for 7.0 hr (10,000 IU/kg) and 11.5 hr (20,000 IU/kg), and for P. multocida for 3.0 hr (10,000 IU/kg) and 4.1 hr (20,000 IU/kg). Pharmacokinetic parameters were calculated by non-compartmental methods. Elimination time half-lives, mean residence time, clearance, and apparent volume of distribution at steady state (Vdss) were all much higher for i.m. injection of 20,000 IU/kg than for i.m. injection of 10,000 IU/kg. We postulate that there exists a minimal tissue-interaction threshold concentration (MTC) at which polymyxin B can enter previously unavailable compartments or bind to previously refractory tissue components. Bioavailability of polymyxin B injected i.m. was 0.904 for the 10,000 IU/kg dose and 0.675 for the 20,000 IU/kg dose. Dosage intervals necessary to produce minimal steady state concentrations (Cssmin) equal to the MIC were calculated. Certain aspects of the use of the parameter Vdss, and limitations on the use of dosage interval calculations for polymyxin B, are discussed. One week after i.m. injection of polymyxin B at 10,000 IU/kg, high tissue drug levels were present, especially in bound form in liver. Following single injections, no toxic effects on turkeys were observed.