Intestinal elimination of ciprofloxacin in rabbits

PBPK Model To Predict Marbofloxacin Distribution in Edible Tissues and Intestinal Exposure in Pigs

Marbofloxacin (MAR) is a fluoroquinolone antibiotic used in food-producing animals in European Union, especially in pigs. In this study, MAR concentrations in plasma, comestible tissues, and intestinal segments were determined in pigs injected with MAR. Based on these data and the literature, a flow-limited PBPK model was developed to predict the tissue distribution of MAR and estimate the withdrawal period after label-use in Europe. A submodel describing the different segments of the intestinal lumen was also developed to assess the intestinal exposure of MAR for the commensal bacteria. During model calibration, only four parameters were estimated. Then, Monte Carlo simulations were performed to generate a virtual population of pigs. The simulation results were compared with the observations from an independent data set during the validation step. A global sensitivity analysis was also carried out to identify the most influential parameters. Overall, the PBPK model was able to adequately predict the MAR kinetics in plasma and edible tissues, as well as in small intestines. However, the simulated concentrations in the large intestine were mostly underestimated, highlighting the need for improvements in the field of PBPK modeling to assess the intestinal exposure of antimicrobials in food animals.

Sex Difference of Effect of Sophora flavescens on Gut Microbiota in Rats

Objective

By observing the sex difference of the gut microbiota in rats and the influence of Sophora flavescens (S. flavescens) on the gut microbiota in rats of different genders, it is hoped that it can provide reference materials for the rational use of S. flavescens in clinical practice.

Method

Taking samples of the jejunum (containing intestinal contents) and feces of 8-week-old rats, and detecting the composition of gut microbiota of females and males by 16S rRNA sequencing technology; At the same time, 8-week-old rats were gavaged with different doses of S. flavescens decoction, and the duodenum, jejunum, ileum, and colon (including the intestinal contents) samples were collected at 1, 2, and 3 weeks, using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) technology and real-time fluorescent quantitative PCR (qRT-PCR) technology to observe the changes in the structure and the quantitative changes of 4 major intestinal dominant bacteria Enterococcus, Bacteriodes, Lactobacillus, and Clostridium in each intestinal segment, respectively.

Result

(1) The gut microbiota of normal rats without administration also had obvious gender differences; (2) S. flavescens significantly affects the composition of gut microbiota, and in different intestinal segments, this effect was different between genders under different dosages and different continuous administration times.

Conclusion

The effect of S. flavescens on the gut microbiota of rats had gender differences.

Intestinal Excretion, Intestinal Recirculation, and Renal Tubule Reabsorption Are Underappreciated Mechanisms That Drive the Distribution and Pharmacokinetic Behavior of Small Molecule Drugs

Drug reabsorption following biliary excretion is well-known as enterohepatic recirculation (EHR). Renal tubular reabsorption (RTR) following renal excretion is also common but not easily assessed. Intestinal excretion (IE) and enteroenteric recirculation (EER) have not been recognized as common disposition mechanisms for metabolically stable and permeable drugs. IE and intestinal reabsorption (IR:EHR/EER), as well as RTR, are governed by dug concentration gradients, passive diffusion, active transport, and metabolism, and together they markedly impact disposition and pharmacokinetics (PK) of small molecule drugs. Disruption of IE, IR, or RTR through applications of active charcoal (AC), transporter knockout (KO), and transporter inhibitors can lead to changes in PK parameters. The impacts of intestinal and renal reabsorption on PK are under-appreciated. Although IE and EER/RTR can be an intrinsic drug property, there is no apparent strategy to optimize compounds based on this property. This review seeks to improve understanding and applications of IE, IR, and RTR mechanisms.

Removal of ciprofloxacin in simulated digestive media by activated charcoal entrapped within zinc-pectinate beads

Beads made of a zinc-pectinate matrix containing activated charcoal were designed for the adsorption of colonic residual antibiotics responsible of the emergence of resistance. Bead stability was shown to correlate with bead zinc content, 0.08 mg/mg being the minimal amount of zinc that protects the egg-box structure against total disintegration. Moreover, the stability in simulated gastro-intestinal media was shown to be related to the composition of the incubation medium. Indeed, gastric medium was shown to extract a large amount of zinc inducing an early disintegration of the beads in the intestinal medium, making necessary their protection by gastro-resistant capsules. Simulated intestinal medium buffered by phosphate was not adapted for the disintegration studies since the formation of a zinc phosphate precipitate on beads surface enhances their resistance to further degradation by pectinases contained in colonic medium. On the other hand, beads incubated in HEPES were stable in intestinal medium and nicely degraded by pectinases contained in simulated colonic medium. Despite this stability, coating with Eudragit RS was needed to prevent the early adsorption of antibiotics in intestinal medium. Adsorption studies in the simulated colonic medium show that the adsorption capacity of activated charcoal is not modified after its encapsulation within pectin beads making the elimination of ciprofloxacin reaching the colon clinically feasible.

Kinetic modelling of passive transport and active efflux of a fluoroquinolone across Caco-2 cells using a compartmental approach in NONMEM

The purpose was to develop a general mathematical model for estimating passive permeability and efflux transport parameters from in vitro cell culture experiments. The procedure is applicable for linear and non-linear transport of drug with time, <10 or >10% of drug transport, negligible or relevant back flow, and would allow the adequate correction in the case of relevant mass balance problems. A compartmental kinetic approach was used and the transport barriers were described quantitatively in terms of apical and basolateral clearances. The method can be applied when sink conditions are not achieved and it allows the evaluation of the location of the transporter and its binding site. In this work it was possible to demonstrate, from a functional point of view, the higher efflux capacity of the TC7 clone and to identify the apical membrane as the main resistance for the xenobiotic transport. This methodology can be extremely useful as a complementary tool for molecular biology approaches in order to establish meaningful hypotheses about transport mechanisms.

Impact of ciprofloxacin in the human-flora-associated (HFA) rat model: Comparison with the HFA mouse model

The ecological impact of different doses of ciprofloxacin was investigated in an experimental germ-free rat model into which human fecal flora was inoculated. Animals received oral doses (gavage) of 0, 0.25, 2.5, and 25 mg/kg body weight (bw) of ciprofloxacin once daily for 5 weeks. All doses of ciprofloxacin significantly reduced aerobic populations. Elimination of Enterobacteriaceae and reduction of bifodibacteria were noticed in the group treated with 25 mg/kg of the antibiotic. The rest of the intestinal flora was not affected. These effects were reversible after the treatment ended. The percentage of resistant enterococci increased in rats treated with 2.5 and 25 mg/kg; however, this increase was not statistically significant. There was a significant (P < 0.05) emergence of ciprofloxacin-resistant Bacteroides fragilis group with 25 mg/kg bw, which is equivalent to a human therapeutic dosage of the antibiotic. The MIC values and the percentage of resistance remained elevated 2 weeks after the end of treatment in this anaerobic population. Although sub-populations of enterococci and Enterobacteriaceae showed decreased susceptibility after ciprofloxacin administration, resistance was not evident. The ability of an exogenous strain of Salmonella to colonize the intestine of animals treated with 25 mg/kg of ciprofloxacin confirmed that the drug disrupted the colonization barrier effect of the indigenous flora at the high dose level tested. No changes in the metabolic parameters occurred during the antibiotic treatment. The results obtained in the HFA rat model were similar to those obtained in our previous study using the HFA mice model where ciprofloxacin at 0.125, 1.25, and 12.5 mg/kg bw induced a decrease of enterococci and Enterobacteriaceae populations. The high dose of ciprofloxacin also induced a decrease in bifidobacteria counts, an increase in levels of resistant B. fragilis group and a significant (P < 0.05) disruption of the colonization resistance of the barrier flora in HFA mice.

Kinetic modelling of the intestinal transport of sarafloxacin. Studies in situ in rat and in vitro in Caco-2 cells

The absorption kinetics of sarafloxacin, as a model of fluoroquinolone structure, were studied in the rat small intestine and in Caco-2 cells. The objective of the study was to investigate the mechanistic basis of the drug's intestinal transport in comparison with other members of the fluoroquinolone family and to apply a mathematical modelling approach to the transport process. In the rat small intestine, sarafloxacin showed dual mechanisms of intestinal absorption with a passive diffusional component and an absorptive carrier-mediated component. The characteristics of the animal study design made it suitable for population analysis, thus allowing the accurate estimation of transport parameters and their inter and intra-individual variances. The transport system in the rat model was ATP-dependent, as sodium azide was able to decrease the absorption rate constant in a concentration-dependent fashion. The inhibition mechanism of sodium azide was modelled based on its ATP depletion capacity. The rationale of this approach was to consider the inhibitor-carrier interaction as a concentration- dependent response. This interaction was accurately described by a non-competitive mechanism. In Caco-2 cells, sarafloxacin showed a concentration dependent permeability in both directions apical to basal, and basal to apical. The permeability values and ratios of permeability values at different concentrations suggested the presence of two carriers (absorption and efflux carriers). The passive diffusion component in both systems was compared to that predicted by the absorption-partition correlation, previously established for two series of fluoroquinolones. The discrepancy between the experimental and predicted value suggested the presence of an efflux mechanism similar to that already described for other fluoroquinolones. The differences and similarities of the in situ and the in vitro results are discussed as well as the usefulness of the modelling approach.

Comparison of faecal and optimal growth conditions on in vitro pharmacodynamic activity of marbofloxacin against Escherichia coli

The objective of the study was to compare the in vitro activity of marbofloxacin against Escherichia coli (E. coli) strains with differing marbofloxacin susceptibility levels under optimal growth conditions and under condition mimicking faecal environment in time-kill kinetic studies. Under optimal growth conditions, marbofloxacin exerted a bactericidal concentration-dependent activity against all E. coli strains with bactericidal concentrations equal to 1 or 4 times MIC. Under faecal growth conditions, marbofloxacin maintained a bactericidal concentration-dependent activity but a 4- to 16-fold increase in bactericidal concentration was required to produce a similar magnitude of effect at 8 h. The bactericidal activity decreased between 8 and 24 h and allowed a residual bacterial population to subsist with a significant regrowth for some of them. Under no-growth conditions, marbofloxacin produced a very low decrease of non-dividing bacteria during a short time. No concentration produced a reduction > or = 3log10 in viable count excepted for two susceptible strains at concentration > or = 64 x MIC after 4 h exposure. The pharmacodynamic parameters from time-kill kinetic studies provide a useful means of studying antimicrobial activity. The importance of using different growth conditions is indicated by the difference in the killing of E. coli in the absence of active dividing cells and in the presence of autoclaved faecal content, both of which have a detrimental effect on the activity of marbofloxacin.

Ciprofloxacin at low levels disrupts colonization resistance of human fecal microflora growing in chemostats

We studied the in vitro effects of a range of ciprofloxacin (CI) concentrations on the human intestinal flora's colonization resistance (CR) to Salmonella kedougou NCTC 12173. Four steady state microbial communities were established in chemostats using inocula from a single pool of human feces. Three chemostats were exposed to CI (0.1, 0.43 and 5 microg/mL, respectively); one served as a no-drug control. The CR of each community was tested by three successive daily challenges of 10(8) S. kedougou, each delivered in a 1 mL bolus. There was no colonization of the no-drug chemostat. Likewise, after exposure to only 0.1 microg/mL CI there was no loss of CR and S. kedougou did not colonize. Conversely, both the 0.43 and the 5 microg/mL-exposed floras suffered a loss of CR and these chemostats were colonized. S. kedougou overgrew faster and reached higher counts in the presence of 0.43 than it did in the presence of 5 microg/mL. One possible explanation is that CI had a dose-dependent effect on both the challenge strain and CR. Thus, at higher levels, even though CR was disrupted by CI, so too was the growth of the challenge strain. Since exposure to CI elicited a dose-dependent reduction in Escherichia coli counts [Reg. Pharmacol. Toxicol. 33 (2001) 276] our new data suggest that E. coli may contribute to the CR against salmonella. We further conclude that, even at fecal levels below those reached during therapy, CI may impact the human gut flora sufficiently to facilitate colonization by S. kedougou.

Pharmacokinetics of ciprofloxacin after single intravenous and repeat oral administration to cats

The pharmacokinetic properties of ciprofloxacin, a second-generation fluoroquinolone, were investigated in six cats after single intravenous and repeat oral administration at a dosage of 10 mg/kg b.i.d. Ciprofloxacin serum concentration was analyzed by microbiological assay using Klebsiella pneumoniae ATCC 10031 as microorganism test. Serum ciprofloxacin disposition was best fitted to a bicompartmental and a monocompartmental open models with first-order elimination after intravenous and oral dosing respectively. After intravenous administration, distribution was rapid (t(1/2(d)), 0.22 +/- 0.23 h) and wide as reflected by the steady-state volume of distribution of 3.85 +/- 1.34 L/kg. Furthermore, elimination was rapid with a plasma clearance of 0.64 +/- 0.28 L/h.kg and a t(1/2(el)) of 4.53 +/- 0.74 h. After repeat oral administration, absorption was rapid with a half-life of 0.23 +/- 0.22 h and T(max) of 1.30 +/- 0.67 h. However bioavailability was low (33 +/- 12%), the peak plasma concentration at steady-state was 1.26 +/- 0.67 microg/mL. Drug accumulation was not significant after seven oral administrations. When efficacy predictors were estimated ciprofloxacin showed a good profile against gram-negative bacteria when administered either intravenously or orally, although its efficacy against gram-positive microorganisms is lower.

Kinetic characterization of secretory transport of a new ciprofloxacin derivative (CNV97100) across Caco-2 cell monolayers

The kinetics of transport of a new fluoroquinolone antibiotic (CNV97100) and its analogs were characterized using the Caco-2 cell culture model. Unidirectional permeabilities of these analogs were greater (p < 0.05) than that of ciprofloxacin. The absorptive permeabilities (P(AB)) of 4'-N-substituted analogs (CNV97101-104) were 400-600% greater, whereas the secretory permeability (P(BA)) was 25-80% greater than unsubstituted analogs because CNV97101-104 were poor substrates for efflux transporters (efflux ratio approximately 1). The transport of compounds without 4'-N-substitution (i.e., ciprofloxacin and CNV97100) favored secretion (efflux ratio approximately 4). Further characterization of CNV97100 transport revealed that it was concentration dependent (apparent K(m) = 0.484 mM, and apparent V(max) = 17.5 nmol x cm(-2) x h(-1)), and temperature dependent (E(a) = 20.57 for P(AB) and 31.45 kcal/mol for P(BA), respectively). p-Glycoprotein (p-gp)inhibitors, such as verapamil (100 microM) and cyclosporin A (CsA, 20 microM) significantly (p < 0.05) inhibited P(BA) but significantly (p < 0.05) enhanced P(AB). Multidrug resistance related protein (MRP) inhibitor leukotriene C(4) only decreased (p < 0.05) P(BA) of ciprofloxacin but not that of CNV97100. In the presence of increasing concentrations of verapamil, the P(BA) of CNV97100 decreased significantly (p < 0.05), with an IC(90) value of 96.5 microM. Taken together, these results suggested that 4'-N-alkylation of fluoroquinolones improves their absorptive permeability. Secretion of CNV97100 is dominated by p-gp, whereas the secretion of ciprofloxacin is via a combination of efflux transporters.

Transepithelial intestinal excretion of ciprofloxacin in humans

The excretion of ciprofloxacin in the small bowel was studied in 40 patients undergoing bowel surgery. Ciprofloxacin (200 mg) was administered iv, and intestinal samples were collected over a 120-min period. In ileal loops ciprofloxacin concentrations reached a peak of 4.0 mg/L, whereas in caecal fluid samples, concentrations were < 0.16 mg/L. Ciprofloxacin administered directly into the ileal and caecal loops did not result in measurable blood levels for 2 h. The results confirm that ciprofloxacin is selectively excreted into the small bowel.

Pharmacokinetics and penetration of danofloxacin into the gastrointestinal tract in healthy and in Salmonella typhimurium infected pigs

The pharmacokinetics and penetration of danofloxacin into the gastrointestinal tract in healthy pigs and in pigs experimentally infected with Salmonella typhimurium were studied. In the infected pigs, a decrease in body clearance and an increase in mean elimination half-life was observed (P < 0.01). Moreover a significant reduction in the volume of the peripheral compartment was found. Danofloxacin distributed well to the gastrointestinal tract achieving high AUC / AUC(plasma)ratios in both groups of pigs. However, compared to the healthy pigs AUC / AUC(plasma)ratios decreased in the infected pigs. Salmonella infection led to an increase in mean residence time (MRT) in the small intestines and lymph nodes and a decrease in MRT in caecum and colon.

Trans-epithelial intestinal elimination of moxifloxacin in rabbits

The intestinal trans-epithelial elimination of moxifloxacin was measured in the jejunum, ileum, caecum and in the bile in a rabbit model. Over a 120 min period following a single parenteral administration of moxifloxacin 15 mg/kg, peak serum concentration was 3.1 (+/- 1.1) mg/L. The elimination constants were: 0.019 (+/- 0. 017) microg/cm(2)/min, 0.011 (+/- 0.014) microg/cm(2)/min and 0.002 (+/- 0.002) microg/cm(2)/min in the jejunum, ileum and caecum, respectively. Per loop, over 120 min, the respective eliminated quantities were: 9.59 (+/- 9.37) microg, 8.26 (+/- 6.74) microg and 1.92 (+/- 1.86) microg. Biliary moxifloxacin concentrations varied between 1.30 and 5.16 mg/L and exceeded serum levels from 45 min onwards. Intestinal concentrations paralleled serum moxifloxacin levels. Altogether, approximately 4.5% of the moxifloxacin dose was eliminated trans-epithelially in the digestive tract over the 120 min experimental period.

Active efflux kinetics of etoposide from rabbit small intestine and colon

The aim of the present study was to investigate the directional transport kinetics of etoposide in rabbit intestinal tissues using side-by-side diffusion chambers. Etoposide is a routinely used mixed-mechanism 'efflux' inhibitor; however, its absorptive and secretory transport kinetics in rabbit intestinal tissues, a commonly used animal model, have not yet been reported. Kinetic studies revealed that the apical (AP) to basolateral (BL) (i.e. absorptive) transport of etoposide was not apparently mediated by specialized transporters, whereas secretion (i.e. BL to AP transport) by intestinal tissues was concentration dependent and saturable. Half-saturation constant values (K(m), mean+/-standard deviation (S.D.)) ranged from 53.6+/-35.8 microM to 168.7+/-127.3 microM, consistent with previous results from our group in intestinal tissues from other species and Caco-2 cell monolayers. Secretory permeability was greatest in the ileum, whereas values in the upper small intestine and colon were approximately equal, and represented only 50% of the value in the ileum. The ileal secretory transport of etoposide was temperature dependent, with the activation energy (E(a)) >4 kCal/mole at 5 microM, suggesting the involvement of the active, energy dependent mechanism. Etoposide inhibition by verapamil and saquinavir, known inhibitors of intestinal secretion, was characterized as competitive with K(i)'s equal to 193.0+/-164.4 microM and 72.6+/-53.5 microM, respectively. The current results demonstrate that the absorptive transport of etoposide in rabbit tissue was not mediated by specialized carriers, and that secretory transport was regionally dependent, mediated by a transporter or transporters, the K(m)'s were in the micromolar range, and involved the energy dependent mechanism(s). The relatively low k(m) of etoposide compared with its aqueous solubility (0.25-0.34 mM, pH 5-6.5, 25 degrees C) makes it the excellent mixed-mechanism competitive inhibitor for determining the secretory transport properties of putative drug substrates. Understanding the in vitro secretory transport kinetics of etoposide provides a mechanistic basis for ongoing studies exploring the functional role of 'efflux' in vivo.

Influence of intravenously administered ciprofloxacin on aerobic intestinal microflora and fecal drug levels when administered simultaneously with sucralfate

Ciprofloxacin, when given intravenously (i.v.), is secreted in significant amounts via the mucosa into the intestinal lumen. Sucralfate inhibits the antimicrobial activity of ciprofloxacin. The effect of combined therapy on the intestinal flora was investigated in 16 healthy volunteers. They were randomly assigned to two groups. Group A received 2 g of sucralfate orally three times a day for 7 days and 400 mg of ciprofloxacin i.v. twice a day (b.i.d.) starting 3 days after the sucralfate administration began. Group B was given only 400 mg of ciprofloxacin i.v. b.i.d. for 4 days. A total of 9 stool samples were collected from each subject beginning the week before ciprofloxacin was administered and on days -1, 1, 2, 3, 4, 7, 9, and 10 or 11 after commencement of the infusion period. The aerobic fecal flora was determined by standard microbiological methods. Measurements of fecal ciprofloxacin levels were based on high-performance liquid chromatography. Counts of bacteria of the family Enterobacteriaceae decreased in all subjects and were below 10(2) CFU/g in eight of eight subjects (group A) and six of eight subjects (group B) on day 4, but they returned to normal in all but one subject (group A) 10 days after the last infusion. The decreases in levels of bacteria of the family Enterobacteriaceae were not significantly different in groups A and B (Kaplan-Meier test). Staphylococci and nonfermenters responded variably, enterococci and lactobacilli remained unchanged, and candida levels increased transiently in four subjects (two in each group). Maximum fecal drug levels ranged from 251 to 811 microg/g. No significant difference could be found between the two groups. The i.v. application of ciprofloxacin eliminates intestinal bacteria of the family Enterobacteriaceae in a rapid and selective manner. This effect is not affected by simultaneous oral application of sucralfate.

Fluoroquinolone (ciprofloxacin) secretion by human intestinal epithelial (Caco-2) cells

1. Human intestinal epithelial Caco-2 cells were used to investigate the mechanistic basis of transepithelial secretion of the fluoroquinolone antibiotic ciprofloxacin. 2. Net secretion and cellular uptake of ciprofloxacin (at 0.1 mM) were not subject to competitive inhibition by sulphate, thiosulphate, oxalate, succinate and para-amino hippurate, probenecid (10 mM), taurocholate (100 microM) or bromosulphophthalein (100 microM). Similarly tetraethylammonium and N-'methylnicotinamide (10 mM) were without effect. 3. Net secretion of ciprofloxacin was inhibited by the organic exchange inhibitor 4,4'-diisothiocyanostilbene-2-2'-disulphonic acid (DIDS, 400 microM). 4. Net secretion of ciprofloxacin was partially inhibited by 100 microM verapamil, whilst net secretion of the P-glycoprotein substrate vinblastine was totally abolished under these conditions. Ciprofloxacin secretion was unaltered after preincubation of cells with two anti-P-glycoprotein antibodies (UIC2 and MRK16), which both significantly reduced secretory vinblastine flux (measured in the same cell batch). Ciprofloxacin (3 mM) failed to inhibit vinblastine net secretin in Caco-2 epithelia, and was not itself secreted by the P-glycoprotein expressing and vinblastine secreting dog kidney cell line, MDCK. 5. Net secretion and cellular uptake of ciprofloxacin (at 0.1 mM) were not subject to alterations of either cytosolic or medium pH, or dependent on the presence of medium Na+, Cl- or K+ in the bathing media. 6. The substrate specificity of the ciprofloxacin secretory transport in Caco-2 epithelia is distinct from both the renal organic anion and cation transport. A role for P-glycoprotein in ciprofloxacin secretion may also be excluded. A novel transport mechanism, sensitive to both DIDS and verapamil mediates secretion of ciprofloxacin by human intestinal Caco-2 epithelia.

Fluoroquinolones in animal health

The fluoroquinolones are a series of synthetic antibacterial agents that are undergoing extensive investigation for both human and veterinary use in the treatment of a variety of bacterial infections. These agents work through the inhibition of DNA gyrase, interfering with the supercoiling of bacterial chromosomal material. As a result, these agents are rapidly bactericidal primarily against gram-negative bacteria, mycoplasma, and some gram-positive bacteria, with most having little to no activity against group D streptococci and obligate anaerobic bacteria. Resistance develops slowly and is almost always chromosomal and not plasmid-mediated. However, development of resistance to the fluoroquinolones and transfer of that resistance among animal and human pathogens have become a hotly debated issue among microbiologists. The fluoroquinolones are a current antimicrobial class whose use in veterinary medicine is being scrutinized. From a pharmacokinetic perspective, these agents are variably but well absorbed from the gastrointestinal tract and almost completely absorbed from parenteral injection sites, and they are well distributed to various tissues in the body. The fluoroquinolones are metabolized and renally excreted, with many of them having approximately equal excretion by the hepatic and the renal excretory systems. The primary toxicity observed at therapeutic doses involves the gastrointestinal system and phototoxicity, although at higher doses central nervous system toxicity and ocular cataracts are observed. Administration to immature animals may result in erosive arthropathies at weight-bearing joints, and administration of high doses to pregnant animals results in maternotoxicity and occasionally embryonic death. The fluoroquinolones are approved for indications such as urinary tract infections and soft tissue infections in dogs and cats and colibacillosis in poultry. Approval for bovine respiratory disease in the United States is being sought. Other indications for which the fluoroquinolones have been used in animal health include deep-seated infections, prostatitis, and other bacterial infections resistant to standard antimicrobial therapy.

Excretion of ciprofloxacin into the large bowel of the rabbit

The intestinal elimination of ciprofloxacin in the large bowel was studied in a rabbit model. Segments from the cecum, colon, and sigmoid colon along with their intact blood vessels were isolated and perfused, and their contents were collected over a 90-min period following the administration of a single parenteral dose of 27 mg of ciprofloxacin per kg of body weight. The elimination rates of ciprofloxacin were 0.126 +/- 0.084 micrograms.min-1.cm-2 in the cecum and 0.264 +/- 0.126, 0.11 +/- 0.07, and 0.21 +/- 0.141 micrograms.min-1.cm-2 in the proximal colon, distal colon, and sigmoid colon, respectively. The calculated fraction of ciprofloxacin eliminated in the large bowel was 3% of the parenteral dose administered. The elimination pattern of ciprofloxacin in the large bowel may explain the unusual activity of this fluoroquinolone in modifying the colonic flora.

Absorption interactions with fluoroquinolones. 1995 update

The utility of the fluoroquinolone class of antibiotics is rapidly expanding due to their favourable pharmacokinetic profile and the continuing development of new compounds. These agents are often used for indications not successfully treated with other orally available antimicrobials in the past, or for 'step-down' therapy in patients originally treated with intravenous agents. As the usage of these agents expands for serious systemic infections, knowledge of absorptive interactions with fluoroquinolones becomes paramount. Fluoroquinolones are often utilised in dosages and against modestly susceptible pathogens which allow a narrow margin for acceptable decreases in bioavailability. Chelation interactions with multivalent cations can result in inactivation of the fluoroquinolone with ramifications in vitro and in vivo. Chelation interactions have been reported to occur in between 22 and 76% of patients prescribed fluoroquinolones. Concurrent administration of magnesium-aluminum antacids and sucralfate has the greatest effect on the bioavailability of quinolones followed by iron, calcium and zinc. Spacing doses of fluoroquinolones and interactants has been suggested as a method of ensuring adequate quinolone absorption, but this can make optimal administration of the cation interactant difficult, if not impossible.

Intestinal elimination of sparfloxacin, fleroxacin, and ciprofloxacin in rats

The intestinal transepithelial elimination of sparfloxacin and fleroxacin was compared with that of ciprofloxacin in a rat model following a single parenteral administration of 25 mg of each of the antibiotics per kg of body weight. All three fluoroquinolones were eliminated through the small intestine. Ciprofloxacin was eliminated in the proximal jejunum at a rate of 1.97 +/- 0.70 micrograms/cm2, while the elimination rates of fleroxacin and sparfloxacin were 0.64 +/- 026 and 0.21 +/- 0.10 micrograms/cm2, respectively, over a 90-min collection period. In the ileum, the elimination rates of ciprofloxacin, fleroxacin, and sparfloxacin over the same period were 1.44 +/- 0.77, 1.00 +/- 0.33, and 0.41 +/- 0.26 micrograms/mc2, respectively. These data suggest that these fluoroquinolones undergo a transepithelial elimination process in the small intestine. This route of elimination may be important in the therapy of bacterial diarrhea.

Role of quinolones in the treatment of diarrhoeal diseases

Diarrhoeal diseases are still an important health problem in both developing and developed countries, and resistance to commonly used antibiotics among enteric pathogens is a major issue. Quinolones have become important agents in the treatment of diarrhoeal diseases because of their excellent in vitro activity against pathogens and their pharmacological features. In many clinical studies, they appeared to be effective in the treatment of shigellosis and the prevention and treatment of diarrhoea in travellers. Several studies have demonstrated that single-dose therapy with these agents is sufficient in many cases. Their role in the treatment of acute salmonellosis is still controversial, because of their lack of efficacy in eliminating salmonella from the faeces.