Experience and expectations of patients on weight loss: The Learning Health System Network Experience.

OBJECTIVE: Weight perception and degree of confidence in achieving healthy lifestyle can be determinants of engagement in obesity interventions. This study explored patients' perceived need for weight loss and the degree of self-confidence in ability to lose weight and sought to identify factors associated with patients' self-confidence in ability to lose weight. METHODS: The authors analysed data from a survey mailed to primary care patients within five sites of the Learning Health Systems Network that explored participants' prior experience with weight management. RESULTS: Among the 2,263 participants who completed the survey section on 'Patients' Experience with Weight Management', perceived need to lose 51 lb or more was statistically significant among those with class III obesity compared with other body mass index (BMI) groups (p value < 0.001). Reported desire to lose weight was also significantly higher among those with the highest BMI than those who were overweight (p value < 0.001). However, this same group had the lowest belief in ability to lose weight (p value < 0.001). In a multiple regression analysis, female gender, higher BMI and need to lose >10 lb were each independently associated with less belief in being able to lose weight. CONCLUSIONS: Patients had varying perceptions on weight loss; those with category III obesity had the highest desire to lose weight but had the least confidence in ability to lose weight. Higher BMI, female gender and need to lose >10 lb were associated with decreased self-confidence in ability to lose weight.

Patient-Centered Network of Learning Health Systems: Developing a resource for clinical translational research.

INTRODUCTION: The Learning Health System Network clinical data research network includes academic medical centers, health-care systems, public health departments, and health plans, and is designed to facilitate outcomes research, pragmatic trials, comparative effectiveness research, and evaluation of population health interventions. METHODS: The Learning Health System Network is 1 of 13 clinical data research networks assembled to create, in partnership with 20 patient-powered research networks, a National Patient-Centered Clinical Research Network. RESULTS AND CONCLUSIONS: Herein, we describe the Learning Health System Network as an emerging resource for translational research, providing details on the governance and organizational structure of the network, the key milestones of the current funding period, and challenges and opportunities for collaborative science leveraging the network.

Management of the patient with diabetic peripheral neuropathy presenting for peripheral regional anesthesia: a European survey and review of literature.

BACKGROUND: Diabetic peripheral neuropathy (DPN) is a frequent complication of longstanding diabetes mellitus. There is no evidence-based consensus whether neuropathic patients undergoing peripheral regional anesthesia are at increased risk of neurologic damage. It is unknown whether these controversial results have been incorporated into clinical practice. We conducted a survey to test the hypothesis that the majority of respondents would consider DPN a potential risk factor for nerve damage in regional anesthesia, and would adapt their technique when performing regional anesthesia. In parallel, we sought to summarize the current knowledge-base regarding regional anesthesia and DPN. METHODS: We therefore performed 1) a literature search to review current literature and 2) an online computer-based survey among members of the European Society of Regional Anesthesia and Pain Therapy (ESRA). RESULTS: The overall response rate was 19% (584 responders/3107 invitations). About a quarter of participants would avoid regional anesthesia in patients with diabetic neuropathy, and 59% of respondents would counsel patients with diabetic neuropathy about increased risk of regional anesthesia. When techniques were modified, most participants would decrease or omit epinephrine, while fewer respondents would decrease dose of local anesthetic or perform other adjustments. More than 80% agreed with the statement that nerve blocks could be performed safely in diabetic neuropathic patients. CONCLUSION: In conclusion, we report the results of the first survey analyzing attitudes and standards of care among European anesthesiologists with regards to regional anesthesia in DPN. While literature is divided on the question whether pre-existing diabetic neuropathy is a risk factor for new neurological deficit after regional anesthesia, most of the responders of this survey take measures to reduce risks, counsel patients on a possible greater risk of neurologic complications, but only a minority of responders would avoid peripheral regional anesthesia altogether.

Inhibition of fibroblast growth factor receptor 1 endocytosis promotes axonal branching of adult sensory neurons.

Fibroblast growth factors (FGFs) promote axon growth during development and regeneration of the nervous system. Among the four types of FGF receptors (FGFRs), FGFR1 is expressed in adult sensory neurons of dorsal root ganglia (DRG), and overexpression of FGFR1 promotes FGF-2-induced elongative axon growth in vitro. Ligand-induced activation of FGFR1 is followed by endocytosis and lysosomal degradation, which leads to the termination of receptor signaling. We previously reported that the lysosomal inhibitor leupeptin enhances FGF-2-induced elongative axon growth of adult DRG neurons overexpressing FGFR1. To better understand the role of subcellular localization of FGFR1 in axon growth, we analyzed the effects of inhibition of endocytosis of FGFR1 on FGF-2-induced neurite outgrowth in PC12 pheochromocytoma cells and adult DRG neurons. The endocytosis inhibitors methyl-ß-cyclodextrin (MßCD) and chlorpromazine enhanced surface localization of FGFR1 in PC12 cells and DRG neurons. Furthermore, MßCD and chlorpromazine increased FGF-2-induced neurite outgrowth of PC12 cells and axonal branching of adult DRG neurons overexpressing FGFR1, whereas MßCD inhibited FGF-2-induced axonal elongation. Analysis of the signaling pathways involved in axon morphology revealed that FGF-2-induced phosphorylation of extracellular signal-regulated kinase (ERK) and Akt was increased by inhibition of FGFR1 endocytosis. Together, our results imply that inhibition of FGFR1 endocytosis by MßCD or chlorpromazine promotes FGF-2-induced axonal branching. The results of this study confirm that internalization of FGFR1 controls axon growth and morphology of adult sensory neurons via selective activation of intracellular signaling pathways.

Metabolic and hormonal effects of oral DHEA in premenopausal women with HIV infection: a randomized, prospective, placebo-controlled pilot study.

Women with HIV infection use dehydroepiandrosterone (DHEA) because of its potential effects on mood and energy. We examined the effects of DHEA on the hypothalamic-pituitary-adrenal and gonadal axes and on insulin sensitivity. Fifteen HIV-positive women were randomized to receive placebo (6 subjects) or oral DHEA (9 subjects). ACTH-, CRF-, and GnRH-stimulation tests were performed before and after 8 weeks of treatment. DHEA, DHEA-S, dihydrotestosterone, total testosterone, free testosterone, sex hormone-binding globulin, estrone, estradiol, cortisol, insulin, IGF-1, IGFBP-1, IGFBP-3, and adiponectin in plasma or serum were measured. There was a significant increase in DHEA (p<0.004), DHEA-S (p<0.008), total testosterone (p<0.008), dihydrotestosterone (p<0.004), androstenedione (p<0.04), and estrone (p<0.03) from baseline within the DHEA group but not within the placebo group. There was a significant increase in DHEA (p<0.0006), DHEA-S (p<0.032), total testosterone (p<0.01), and dihydrotestosterone (p<0.005) in the DHEA group compared with the placebo group. Oral DHEA produces significant increases in circulating DHEA, DHEA-S, testosterone, DHT, and, possibly, androstenedione and estrone levels in premenopausal women with HIV infection. In the current pilot study these hormone changes did not affect the pituitary or adrenal axis or insulin/IGF indices. Long-term studies with larger groups of patients are needed to confirm these data and to determine their clinical significance.

Differential neurotoxicity of tricyclic antidepressants and novel derivatives in vitro in a dorsal root ganglion cell culture model.

BACKGROUND AND OBJECTIVE: Tricyclic antidepressants are commonly employed orally to treat major depressive disorders and have been shown to be of substantial benefit in various chronic pain conditions. Among other properties they are potent Na+ channel blockers in vitro and show local anaesthetic properties in vivo. The present study aimed to determine their differential neurotoxicity, and that of novel derivatives as prerequisite for their potential use in regional anaesthesia. METHODS: To directly test neurotoxicity in adult peripheral neurons, the culture model of dissociated adult rat primary sensory neurons was employed. Neurons were incubated for 24 h with amitriptyline, N-methyl-amitriptyline, doxepin, N-methyl-doxepin, N-propyl-doxepin, desipramine, imipramine and trimipramine at 100 mumol, and at concentrations correlating to their respective potency in blocking sodium channels. RESULTS: All investigated substances showed considerable neurotoxic potency as represented in significantly decreased neuron numbers in cultures as compared to controls. Specifically, doxepin was more neurotoxic than amitriptyline, and both imipramine and trimipramine were more toxic than desipramine or amitriptyline. Novel derivatives of tricyclic antidepressants were, in general, more toxic than the parent compound. CONCLUSIONS: Tricyclic antidepressants and novel derivatives thereof show differential neurotoxic potential in vitro. The rank order of toxicity relative to sodium channel blocking potency was desipramine < amitriptyline < N-methyl amitriptyline < doxepin < trimipramine < imipramine < N-methyl doxepin < N-propyl doxepin.

Effect of cardiolipin oxidation on solid-phase immunoassay for antiphospholipid antibodies.

Diagnostic assays for antiphospholipid antibodies are routinely performed on microtitre plates coated with cardiolipin. Here we show that contact between cardiolipin and NUNC-Immuno plates leads to extensive oxidation, generating a series of peroxy-cardiolipins which were identified by electrospray ionization mass spectrometry. To investigate the impact of oxidation on the antibody assay. cardiolipin was resolved into 12 molecular species, including oxidized species and non-oxidized species with different degrees of unsaturation. All 12 species reacted under anaerobic conditions with serum from patients with primary antiphospholipid syndrome. Immune reactivity was similar for tetralinoleoyl-cardiolipin, trilinoleoyl-oleoyl-cardiolipin, and peroxycardiolipins, but somewhat lower for tristearoyl-oleoyl-cardiolipin. Oxidative treatment of cardiolipin with air, cytochrome c, or Cu2+/tert-butylhydroperoxide, either before or during the assay, did not enhance immune reactivity. Similar results were obtained with a monoclonal IgM from lupus-prone mice, that binds cardiolipin in the absence of protein cofactors. We conclude that the solid-phase assay for antiphospholipid antibodies can be supported by various oxidized and non-oxididized molecular species of cardiolipin.

Energy balance, viral burden, insulin-like growth factor-1, interleukin-6 and growth impairment in children infected with human immunodeficiency virus.

OBJECTIVE: To determine the relationship between energy metabolism and growth abnormalities in HIV-infected children and to assess clinical or laboratory characteristics which may be contributing factors to their growth impairment. DESIGN: A comparative study. METHODS: We measured energy intake by inpatient calorie count/outpatient 24 h food recalls, resting energy expenditure by indirect calorimetry, total energy expenditure by the doubly-labeled water technique, iron metabolism, protein metabolism, and lipid metabolism markers as well as CD4 count, viral load, insulin-like growth factor-1 (IGF-1), serum interleukin-6 (IL-6), and whole blood stimulated IL-6 levels in prepubertal congenitally HIV-infected children with normal and impaired growth patterns. RESULTS AND CONCLUSIONS: Differences in energy expenditures were not found between normal and growth-impaired HIV-infected children. Energy intake but not energy expenditure was significantly reduced when HIV-infected children were compared to expected normal values for age and gender. Advanced HIV clinical disease, severe immune suppression, increased viral burden, increased IL-6 activity, decreased total serum protein, and decreased IGF-1 levels were more likely to be found in HIV-infected children with growth impairment in comparison with HIV-infected children with normal growth.

The obese gene is expressed in lean littermates of the genetically obese mouse (C57BL/6J ob/ob).

Some individuals of the mixed group of "lean" littermates (+/ob and +/+) of (C57BL/6J ob/ob) often suggest phenotypic characteristics of ob/ob animals. Therefore, it was of interest to determine whether expression of the ob gene had physiological significance in +/ob animals. Body weight (BW), fasting blood glucose (FBG), and body core temperature (Tr) were monitored between 62 and 364 days of age in +/+ and +/ob mice. Among females but not males, +/ob mice were heavier (P = 0.003) and FBG levels were greater (P = 0.04) than in +/+ animals. Comparison of Tr indicated differences suggesting falling Tr in +/ob but rising Tr in +/+ mice with age in males but not females. Multivariate analysis of variance yielded genotype effects for both males (P = 0.002) and females (P = 0.02). BW, FBG, and Tr alone were sufficient at the 75% level for genotypic characterization and separation of +/? animals as +/ob or +/+; clearly, expression of the ob gene in heterozygotes of the +/ob animal may make the mixed +/? group inappropriate as lean controls.

Substrate inhibition of D-amino acid transaminase and protection by salts and by reduced nicotinamide adenine dinucleotide: isolation and initial characterization of a pyridoxo intermediate related to inactivation.

D-Amino acid transaminase, a pyridoxal phosphate (PLP) enzyme, is inactivated by its natural substrate, D-alanine, concomitant with its alpha-decarboxylation [Martinez del Pozo, A., Yoshimura, T., Bhatia, M. B., Futaki, S., Manning, J. M., Ringe, D., and Soda, K. (1992) Biochemistry 31, 6018-6023; Bhatia, M. B., Martinez del Pozo, A., Ringe, D., Yoshimura, T., Soda, K., and Manning, J. M. (1993) J. Biol. Chem. 268, 17687-17694]. beta-Decarboxylation of d-aspartate to d-alanine leads also to this inactivation [Jones, W. M., van Ophem, P. W., Pospischil, M. A., Ringe, D., Petsko, G., Soda, K., and Manning, J. M. (1996) Protein Sci. 5, 2545-2551]. Using a high-performance liquid chromatography-based method for the determination of pyridoxo cofactors, we detected a new intermediate closely related to the inactivation by d-alanine; its formation occurred at the same rate as the inactivation and upon reactivation it reverted to PLP. Conditions were found under which it was characterized by ultraviolet-visible spectral analysis and mass spectroscopy; it is a pyridoxamine phosphate-like compound with a C2 fragment derived from the substrate attached to the C'-4 of the pyridinium ring and it has a molecular mass of 306 consistent with this structure. In the presence of d-serine, slow accumulation of a quinonoid intermediate is also related to inactivation. The inactivation can be prevented by salts, which possibly stabilize the protonated aldimine coenzyme complex. The reduced cofactor, nicotinamide adenine dinucleotide, prevents D-aspartate-induced inactivation. Both of these events also are related to formation of the novel intermediate.

Structure of chain d of the gigantic hemoglobin of the earthworm.

The extracellular hemoglobin of the earthworm has four major O2-binding chains, a, b, c and d, together with additional non-heme structural chains that are required for assembly. Although the abc trimer self-associates extensively at least to (abc)10, addition of chain d results in the formation of a discrete 280 kDa complex corresponding to (abcd)4. Thus a primary function of chain d is to cap the abc association and convert an abc trimer that binds O2 with weak cooperativity to a highly cooperative (abcd)4 complex. Amino-acid sequences of the major globin chains a, b, c have been determined previously by peptide and cDNA analysis. However, the peptide sequence reported for the major chain d (Shishikura, F., Snow, J.W., Gotoh, T., Vinogradov, S.N. and Walz, D.A. (1987) J. Biol. Chem., 262. 3123-3131), has a calculated molecular mass 134-167 Da higher than masses for components of chain d determined by mass spectrometry (Owrby, D.W., Zhu, H., Schneider, K., Beavis, R.C., Chait, B.T. and Riggs, A.F. (1993) J. Biol. Chem. 268, 13539-13547). Reverse-phase HPLC confirms the presence of two distinct polypeptides, d1 and d2, together with d'1, a variant of d1, cDNA derived amino acid sequences have been determined for chains d'1 and d2 by application of the polymerase chain reaction with primers based on the NH2-terminal sequences and oligo-dT. Each of the two cDNA-derived sequences has 140 residues and they differ by 28 substitutions. The data show that the sequence originally reported had been derived from peptides generated from both polypeptides.

Collision induced decomposition of peptides. Choice of collision parameters.

Collision-induced dissociation product ion spectra of a series of doubly charged tryptic peptide ions produced by electrospray ionization were obtained by triple-quadrupole tandem mass spectrometry. The sequence information content of the product ion spectra was explored as a function of collision energy and collision-cell gas pressure for parent ions with molecular masses ranging from 300 to 2000 u. The energy range (at a given pressure) in which the degree of fragmentation is acceptable was found to be narrow for parent ions of a given mass, and the optimal collision energy was observed to exhibit a strong linear correlation with parent ion mass. This observed correlation opens the way for on-line software-controled selection of optimal mass spectrometric conditions in the enzymatic digestion-liquid chromatography-tandem mass spectrometric strategy of amino acid sequencing of proteins.

Anti-tumor necrosis factor antibody treatment of recurrent bacteremia in a baboon model.

Timely intervention in recurrent episodes of sepsis poses a major problem in intensive care, because the diagnosis is often made after the onset of sepsis, delaying the initiation of treatment. There are only a few animal models that cover this situation. We have developed a baboon model of recurrent bacteremia (3 x 2 h intravenous infusion of 1 x 10(8) CFU Escherichia coli/kg), which leads to late organ failure. In this model (tested on 16 animals) we began anti-tumor necrosis factor antibody treatment (BAYX 1351; Bayer AG, 7.5 mg/kg or saline placebo) after the first bacteremic episode (+4 h), which significantly (p < .05) protected animals from death, none out of eight (100% survival), in the treatment group in contrast to four animals out of eight died (50% survival) in the placebo group. This effect was also reflected in improved organ function and in attenuated cytokine and plasminogen activator inhibitor release. From these studies we conclude that the delayed application of anti-tumor necrosis factor antibodies in recurrent bacteremia is a powerful tool for preventing septic death.

Evaluation of ciprofloxacin alone and in combination with other antibiotics in a murine model of thigh muscle infection.

The therapeutic efficacies of ciprofloxacin and some comparative drugs were evaluated in a model of thigh muscle infection in neutropenic mice. Ciprofloxacin was found to be highly effective against all gram-negative and gram-positive bacteria tested. Combinations of ciprofloxacin and either gentamicin or beta-lactam antibiotics exhibited additive or slightly synergistic effects against the Enterobacteriaceae and gram-positive isolates. Azlocillin was found to increase significantly the efficacy of ciprofloxacin against Pseudomonas aeruginosa. Antagonistic interactions with vancomycin, which impaired the bactericidal activity of ciprofloxacin against Streptococcus faecalis, were observed only in vitro but not in vivo, whereas erythromycin also slightly reduced the therapeutic efficacy of ciprofloxacin in vivo.

Distribution of [14C]-ciprofloxacin in experimentally induced intramuscular abscesses of rats.

Wistar rats were infected by injection of 0.05 ml of a dense oily suspension of Staphylococcus aureus into the posterior thigh muscles of the hind leg. Three days later, solid abscesses had formed which were characterized by a peripheral accumulation of polymorphocytes and incipient central necrosis. At this time, 10 mg/kg of [14C]-ciprofloxacin (1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-7-piperazin-1-ylquino line-3-carboxylic acid, Bay o 9867; designated tradename: Ciprobay) were administered intravenously. The animals were sacrificed at various time intervals after treatment and the distribution of radioactivity was examined by whole-body autoradiography. Five min after administration of ciprofloxacin, the radioactivity was found to be differentially distributed among all organs and tissues, but no radioactivity was detectable in the abscess. Beginning from 1 h post appl., increasing relative amounts of radioactivity were seen inside the abscesses. The relative enrichment as compared to the surrounding muscle tissue was most pronounced after 5 h, indicating that the radioactivity was eliminated more rapidly from the muscle than from the abscess. Some radioactivity was still present in the abscess 8 h after treatment of the animals. The comparison of autoradiograms and corresponding histological sections revealed a distinct affinity of [14C]-ciprofloxacin and/or its potential radioactive metabolites to the areas of inflammatory cellular infiltrates.

Comprehensive evaluation of ciprofloxacin in combination with beta-lactam antibiotics against Enterobacteriaceae and Pseudomonas aeruginosa.

1-cyclopropyl-6-fluoro-1, 4-dihydro-4-oxo-7-piperazine-1-ylquinoline-3-carboxylic acid (ciprofloxacin, Bay o-9867, Bay q-3939) was evaluated by checkerboard assay in combination with ampicillin, ticarcillin, mezlocillin, azlocillin, piperacillin, cefamandole, cefoxitin, cefotaxime, and ceftazidime. A total of 220 clinical isolates of enterobacteriaceae and Pseudomonas aeruginosa (11 species, 20 strains each) were examined. Predominantly additive combination effects were seen with all antibiotic combinations tested. Synergy was obtained with only a few test strains while antagonistic drug interactions were not observed at all. Time-kill experiments which were performed to assess the bactericidal activities, confirmed these findings. The antibiotic combinations were also evaluated in vivo using a model of experimental thigh muscle infection in neutropenic mice. In-difference or additive therapeutic effects resulted when the beta-lactam compounds and ciprofloxacin were given in combination at doses which were also effective alone. Subinhibitory doses of azlocillin and mezlocillin, on the other hand, appeared to increase the efficacy of ciprofloxacin. The influence of various application schedules was examined by time-kill experiments and in mice. Sequential administration of the drugs at intervals of 2 h did not alter the combination effects regardless of the sequence of administration.

Comprehensive evaluation of ciprofloxacin-aminoglycoside combinations against Enterobacteriaceae and Pseudomonas aeruginosa strains.

The in vitro activities of antibiotic combinations containing ciprofloxacin and either gentamicin, sisomicin, netilmicin, amikacin, or tobramycin were evaluated by checkerboard assay (agar dilution method). A total of 220 strains of Enterobacteriaceae and Pseudomonas aeruginosa (11 species, 20 strains each) were tested. Synergistic or antagonistic effects were observed in less than 1% of the tests performed; they appeared to represent method-dependent fluctuations rather than true antibiotic interactions. No significant differences among the five aminoglycosides tested were seen. Time-kill experiments performed with three representative strains of Escherichia coli and Serratia marcescens showed additive combination effects with respect to the kill rates and inhibition of bacterial regrowth. Exposure of Serratia strains to either ciprofloxacin or gentamicin before the addition of the second drug had little influence on the combination effects observed. No antagonistic drug interactions were seen in vivo when combination therapy with ciprofloxacin and gentamicin was evaluated in a model of E. coli thigh muscle infection in neutropenic mice. Comparable therapeutic effects were obtained, regardless of whether the two compounds were administered simultaneously or sequentially at 1- or 2-h intervals.

Mode of action of clotrimazole: implications for therapy.

Ergosterol is an essential constituent of the fungal cytoplasmic membrane. Clotrimazole and other azoles interfere with the ergosterol biosynthesis in a concentration-dependent fashion. Although low concentrations exhibit only a partially inhibitory effect, high concentrations may completely block ergosterol synthesis. Reduction of fungal growth and inhibition of growth and fungicidal action during prolonged incubation are the corresponding effects at the cellular level that are a consequence of ergosterol depletion. The inoculum effect, the influence of the incubation period, and the influence of nutrient media, three factors that often complicate susceptibility testing in vitro, can also be explained by the mode of action of azole compounds. Another interesting characteristic of azole antifungals was revealed by the observation that hyphae and pseudomycelia of Candida albicans are much more susceptible to azoles than are yeast cells. Even 1% of the minimum inhibitory concentration of clotrimazole may totally inhibit mycelial growth in vitro. This may be of clinical importance, since germination was reported to enhance adherence of C. albicans to buccal and vaginal epithelial cells.

Effects of cimetidine, nitrite, cimetidine plus nitrite, and nitrosocimetidine on tumors in mice following transplacental plus chronic lifetime exposure.

Cimetidine (CM), a drug widely prescribed for ulcers, readily undergoes nitrosation to form nitrosocimetidine (NCM), a genotoxic agent. In a test of the chronic effects of NCM in mice, (C57BL/6 X BALB/c)F1 mice were exposed chronically to NCM (113 or 1130 ppm) in the drinking water from preconception through prenatal and neonatal development and adult life. Each group consisted of 40 to 80 mice of each sex, and median survival time was 27 months. Other groups were given CM alone or in combination with NaNO2 (184 or 1840 ppm), or NaNO2 alone. None of the chemical treatments had large effects on reproductive parameters, survival, or incidence of nonneoplastic lesions. CM treatment was associated with a small but significant increase in incidence of lymphomas in females, 41 of 59 (69%), compared with 31 of 66 controls (47%, P = 0.01). No females receiving either dose of NCM developed mammary carcinomas (0 of 91), compared with an incidence of four of 66 controls (6%, P = 0.03). Males given the high-dose combination of CM and NaNO2 showed a higher incidence of lung tumor bearers than controls (71 of 79 versus 30 of 52, P less than 0.01) and also experienced a significant, dose-dependent increase in numbers of large lung tumors (greater than 1 cm in diameter), lung carcinoma, and metastatic lung tumors. Females given the higher dose of NCM had significantly greater incidence of mice with large lung tumors than controls (nine of 41 versus three of 66, P = 0.009). The possibility of carcinogenicity of cimetidine, nitrosocimetidine, and cimetidine plus nitrite is discussed.

Penetration of antibiotics through cell culture monolayers.

Commercial tissue culture chambers were modified in such a way that they contained two portions of medium separated by a horizontal membrane. When grown on this membrane, Vero (monkey kidney) cells formed continuous cell monolayers. By comparing the penetration of antibiotics through monolayer-covered and cell-free membranes, the retention brought about by the cell layer could be measured. Only minor differences were seen between oxacillin, mezlocillin and ciprofloxacin. Penetration of polymyxin B through the cell layer proved to be reduced by about 40% in comparison to oxacillin.