Blood, tissue, and intracellular concentrations of azithromycin during and after end of therapy.

Although azithromycin is extensively used in the treatment of respiratory tract infections as well as skin and skin-related infections, pharmacokinetics of azithromycin in extracellular space fluid of soft tissues, i.e., one of its therapeutic target sites, are not yet fully elucidated. In this study, azithromycin concentration-time profiles in extracellular space of muscle and subcutaneous adipose tissue, but also in plasma and white blood cells, were determined at days 1 and 3 of treatment as well as 2 and 7 days after the end of treatment. Of all compartments, azithromycin concentrations were highest in white blood cells, attesting for intracellular accumulation. However, azithromycin concentrations in both soft tissues were markedly lower than in plasma both during and after treatment. Calculation of the area under the concentration-time curve from 0 to 24 h (AUC(0-24))/MIC(90) ratios for selected pathogens suggests that azithromycin concentrations measured in the present study are subinhibitory at all time points in both soft tissues and at the large majority of observed time points in plasma. Hence, it might be speculated that azithromycin's clinical efficacy relies not only on elevated intracellular concentrations but possibly also on its known pleotropic effects, including immunomodulation and influence on bacterial virulence factors. However, prolonged subinhibitory azithromycin concentrations at the target site, as observed in the present study, might favor the emergence of bacterial resistance and should therefore be considered with concern. In conclusion, this study has added important information to the pharmacokinetic profile of the widely used antibiotic drug azithromycin and evidentiates the need for further research on its potential for induction of bacterial resistance.

Blood, tissue, and intracellular concentrations of erythromycin and its metabolite anhydroerythromycin during and after therapy.

For macrolides, clinical activity but also the development of bacterial resistance has been attributed to prolonged therapeutic and subtherapeutic concentrations. Although erythromycin is a long-established antimicrobial, concomitant determination of the pharmacokinetics of erythromycin and its metabolites in different compartments is limited. To better characterize the pharmacokinetics of erythromycin and its anhydrometabolite (anhydroerythromycin [AHE]) in different compartments during and after the end of treatment with 500 mg of erythromycin four times daily, concentration-time profiles were determined in plasma, interstitial space of muscle and subcutaneous adipose tissue, and white blood cells (WBCs) at days 1 and 3 of treatment and 2 and 7 days after end of therapy. In WBCs, concentrations of erythromycin exceeded those in plasma approximately 40-fold, while free concentrations in plasma and tissue were comparable. The observed delay of peak concentrations in tissue might be caused by fast initial cellular uptake. Two days after the end of treatment, subinhibitory concentrations were observed in plasma and interstitial space of both soft tissues, while 7 days after the end of treatment, erythromycin was not detectable in any compartment. This relatively short period of subinhibitory concentrations may be advantageous compared to other macrolides. The ratio of erythromycin over AHE on day 1 was highest in plasma (2.81 ± 3.45) and lowest in WBCs (0.27 ± 0.22). While the ratio remained constant between single dose and steady state, after the end of treatment the concentration of AHE declined more slowly than that of the parent compound, indicating the importance of the metabolite for the prolonged drug interaction of erythromycin.

Comparable population pharmacokinetics and pharmacodynamic breakpoints of cefpirome in cystic fibrosis patients and healthy volunteers.

Cystic fibrosis (CF) patients are often reported to have higher clearances and larger volumes of distribution per kilogram of total body weight (WT) for beta-lactams than healthy volunteers. As pharmacokinetic (PK) data on cefpirome from studies of CF patients are lacking, we systematically compared its population PK and pharmacodynamic breakpoints for CF patients and healthy volunteers of similar body size. Twelve adult CF patients (median lean body mass [LBM] = 45.7 kg) and 12 healthy volunteers (LBM = 50.0 kg) received a single 10-min intravenous infusion of 2 g cefpirome. Plasma and urine concentrations were determined by high-performance liquid chromatography (HPLC). Population PK and Monte Carlo simulations were performed using NONMEM and S-ADAPT and a duration of an unbound plasma concentration above the MIC ≥ 65% of the dosing interval as a pharmacodynamic target. Unscaled clearances for CF patients were similar to those seen with healthy volunteers, and the volume of distribution was 6% lower for CF patients. Linear scaling of total clearance by WT resulted in clearance that was 20% higher (P ≤ 0.001 [nonparametric bootstrap]) in CF patients. Allometric scaling by LBM explained the differences between the two subject groups with respect to average clearance and volume of distribution and reduced the unexplained between-subject variability of renal and nonrenal clearance by 10 to 14%. For the CF patients, robust (>90%) probabilities of target attainment (PTA) were achieved by the administration of a standard dose of 2 g/70 kg WT every 12 h (Q12h) given as 30-min infusions for MICs ≤ 1.5 mg/liter. As alternative dosage regimens, a 5-h infusion of 1.33 g/70 kg WT Q8h achieved robust PTAs for MICs ≤ 8 to 12 mg/liter and a continuous infusion of 4 g/day for MICs ≤ 12 mg/liter. Prolonged infusion of cefpirome is expected to be superior to short-term infusions for MICs between 2 and 12 mg/liter.

Penetration of meropenem into epithelial lining fluid of patients with ventilator-associated pneumonia.

Antibiotic penetration to the infection site is critical for obtaining a good clinical outcome in patients with ventilator-associated pneumonia (VAP). Surprisingly few studies have quantified the penetration of ß-lactam agents into the lung, as measured by the ratio of area under the concentration-time curve (AUC) in epithelial lining fluid (ELF) to AUC in plasma (AUC(ELF)/AUC(plasma) ratio). These have typically involved noninfected patients. This study examines the penetration and pharmacodynamics of meropenem in the ELF among patients with VAP. Meropenem plasma and ELF concentration-time data were obtained from patients in a multicenter clinical trial. Concentration-time profiles in plasma and ELF were simultaneously modeled using a three-compartment model with zero-order infusion and first-order elimination and transfer (big nonparametric adaptive grid [BigNPAG]). A Monte Carlo simulation was performed to estimate the range of ELF/plasma penetration ratios one would expect to observe in patients with VAP, as measured by the AUC(ELF)/AUC(plasma) ratio. The range of AUC(ELF)/AUC(plasma) penetration ratios predicted by the Monte Carlo simulation was large. The 10th percentile of lung penetration was 3.7%, while the 90th percentile of penetration was 178%. The variability of ELF penetration is such that if relatively high ELF exposure targets are required to attain multilog kill or resistance suppression for bacteria like Pseudomonas aeruginosa, then even receiving the largest licensed dose of meropenem with an optimal prolonged infusion may not result in target attainment for a substantial fraction of the population.

Population pharmacokinetic comparison and pharmacodynamic breakpoints of ceftazidime in cystic fibrosis patients and healthy volunteers.

Despite the promising activity of ceftazidime against Pseudomonas aeruginosa and Burkholderia cepacia, there has not yet been a study that directly compared the pharmacokinetics (PK) of ceftazidime in cystic fibrosis (CF) patients and healthy volunteers by population PK methodology. We assessed the population PK and PK/pharmacodynamic (PD) breakpoints of ceftazidime in CF patients and healthy volunteers. Eight CF patients (total body weight [WT] [average +/- standard deviation] = 42.9 +/- 18.4 kg) and seven healthy volunteers (WT = 66.2 +/- 4.9 kg) received 2 g ceftazidime as a 5-min intravenous infusion. High-performance liquid chromatography (HPLC) was used for drug analysis, and NONMEM (results reported), S-ADAPT, and NPAG were used for parametric and nonparametric population PK modeling. We considered linear and allometric body size models to scale clearance and volume of distribution. Monte Carlo simulations were based on a target time of non-protein-bound plasma concentration of ceftazidime above MIC of > or =65%, which represents near-maximal killing. Unscaled total clearance was 19% lower in CF patients, and volume of distribution was 36% lower. Total clearance was 7.82 liters/h for CF patients and 6.68 liters/h for healthy volunteers with 53 kg fat-free mass. Allometric scaling by fat-free mass reduced the between-subject variability by 32% for clearance and by 18 to 26% for volume of both peripheral compartments compared to linear scaling by WT. A 30-min ceftazidime infusion of 2 g/70 kg WT every 8 h (q8h) achieved robust (> or =90%) probabilities of target attainment (PTAs) for MICs of < or =1 mg/liter in CF patients and < or =3 mg/liter in healthy volunteers. Alternative modes of administration achieved robust PTAs up to markedly higher MICs of < or =8 to 12 mg/liter in CF patients for 5-h infusions of 2 g/70 kg WT q8h and < or =12 mg/liter for continuous infusion of 6 g/70 kg WT daily.

New semiphysiological absorption model to assess the pharmacodynamic profile of cefuroxime axetil using nonparametric and parametric population pharmacokinetics.

Cefuroxime axetil is widely used to treat respiratory tract infections. We are not aware of a population pharmacokinetic (PK) model for cefuroxime axetil. Our objectives were to develop a semiphysiological population PK model and evaluate the pharmacodynamic profile for cefuroxime axetil. Twenty-four healthy volunteers received 250 mg oral cefuroxime as a suspension after a standardized breakfast. Liquid chromatography-tandem mass spectrometry was used for drug analysis, NONMEM and S-ADAPT (results reported) were used for parametric population PK modeling, and NPAG was used for nonparametric population PK modeling. Monte Carlo simulations were used to predict the duration for which the non-protein-bound-plasma concentration was above the MIC (fT(>MIC)). A model with one disposition compartment, a saturable and time-dependent drug release from the stomach, and fast drug absorption from the intestine yielded precise (r > 0.992) and unbiased curve fits and an excellent predictive performance. The apparent clearance was 21.7 liters/h (19.8% coefficient of variation [CV]) and the volume of distribution 38.7 liters (18.3% CV). Robust (>or=90%) probabilities of target attainment (PTAs) were achieved by 250 mg cefuroxime given every 12 h (q12h) or q8h for MICs of MIC) of >or=40% and for MICs of MIC) of >or=65%. For the >or=40% fT(>MIC) target, the PTAs for 250 mg cefuroxime q12h were >or=97.8% for Streptococcus pyogenes and penicillin-susceptible Streptococcus pneumoniae. Cefuroxime at 250 mg q12h or q8h achieved PTAs below 73% or 92%, respectively, for Haemophilus influenzae, Moraxella catarrhalis, and penicillin-intermediate S. pneumoniae for susceptibility data from various countries. Depending on the MIC distribution, 250 mg oral cefuroxime q8h instead of q12h should be considered, especially for more-severe infections that require near-maximal killing by cefuroxime.

Impact of spore biology on the rate of kill and suppression of resistance in Bacillus anthracis.

Bacillus anthracis is complex because of its spore form. The spore is invulnerable to antibiotic action. It also has an impact on the emergence of resistance. We employed the hollow-fiber infection model to study the impacts of different doses and schedules of moxifloxacin on the total-organism population, the spore population, and the subpopulations of vegetative- and spore-phase organisms that were resistant to moxifloxacin. We then generated a mathematical model of the impact of moxifloxacin, administered by continuous infusion or once daily, on vegetative- and spore-phase organisms. The ratio of the rate constant for vegetative-phase cells going to spore phase (K(vs)) to the rate constant for spore-phase cells going to vegetative phase (K(sv)) determines the rate of organism clearance. The continuous-infusion drug profile is more easily sensed as a threat; the K(vs)/K(sv) ratio increases at lower drug exposures (possibly related to quorum sensing). This movement to spore phase protects the organism but makes the emergence of resistance less likely. Suppression of resistance requires a higher level of drug exposure with once-daily administration than with a continuous infusion, a difference that is related to vegetative-to-spore (and back) transitioning. Spore biology has a major impact on drug therapy and resistance suppression. These findings explain why all drugs of different classes have approximately the same rate of organism clearance for Bacillus anthracis.

Biosimilarity of HX575 (human recombinant epoetin alfa) and epoetin beta after multiple subcutaneous administration.

OBJECTIVE: To compare the steady-state pharmacokinetics and pharmacodynamics following multiple subcutaneous administration of a new erythropoiesis stimulating agent (HX575, Binocrit, Sandoz GmbH, Holzkirchen, Germany) with that of epoetin beta (NeoRecormon, Roche Ltd., Welwyn Garden City, UK). METHODS: An open, randomized, parallel group study was conducted in 80 healthy adult males. Subjects were randomized to multiple subcutaneous doses of 100 IU/kg body weight of HX575 or epoetin beta three-times-weekly for 4 weeks. Serum epoetin concentrations were measured using an enzyme-linked immunosorbent assay (ELISA) and pharmacokinetic parameters for the two treatments were compared. The time course and area under the effect curve ratios of hematological characteristics were used as surrogate parameters for efficacy evaluation. RESULTS: The pharmacokinetic profiles after multiple doses were similar for both treatments. HX575 was bioequivalent to epoetin beta with respect to the rate and extent of exposure of exogenous epoetin, as indicated by the ratios (90% confidence intervals) of AUC(tau) (96.1 (86.4 - 106.9)) and C(max,ss) (98.5 (85.2 - 113.9)). The hematological profiles of both treatments were similar as determined from the population mean curves and the AUEC(Hb) ratio (90% confidence interval] (99.2 (97.7 - 100.7)), the primary endpoint of this study. Study medication was well tolerated with no clinically relevant differences between safety profiles of the treatments. Anti-epoetin antibodies were not detected at any time. CONCLUSIONS: HX575 and epoetin beta were bioequivalent with respect to their steady-state pharmacokinetic profile and pharmacodynamic action. These results support the conclusion that HX575 and epoetin beta will be equally efficacious and may be interchangeable as therapy.

The role of silver nitrate as additive in non-aqueous capillary electrophoresis.

In this study, effect of use of silver nitrate as additive on non-aqueous capillary electrophoresis (NACE) separations of some structurally related compounds belonging to antidepressants, neuroleptics or sulfonamides, was examined. The presence of silver nitrate was found to enhance these NACE separations. The use of silver nitrate provided a successful method of improving the separations of antidepressants, neuroleptics and sulfonamides. The use of cyanomethyl-calix[4]arene (CMCX[4]) in the presence of silver nitrate for the separation of sulfonamides has significantly affected the separation.

Bioavailability of amoxicillin and clavulanic acid from extended release tablets depends on intragastric tablet deposition and gastric emptying.

The rate and extent of amoxicillin and clavulanic acid absorption from pharmacokinetically enhanced extended release (ER) tablets is strongly influenced by the intake conditions. In order to investigate the cause of the food effects, a pharmacokinetic study with simultaneous imaging of the in vivo behaviour of the ER tablets by magnetic marker monitoring (MMM) was performed. Under fasting conditions the amoxicillin AUC (1854+/-280microg min ml(-1)) was significantly lower than after intake at the beginning of the breakfast (2452+/-354microg min ml(-1)) or after the breakfast (2605+/-446microg min ml(-1)). In contrast, clavulanic acid AUC was well comparable after tablet intake under fasting conditions and intake at the beginning of a breakfast (191+/-46 and 189+/-44microg min ml(-1), respectively) but significantly lower following a breakfast (126+/-71microg min ml(-1)). The localization data showed that the reduced bioavailability of amoxicillin under fasting conditions is due to early gastric emptying in combination with poor absorption from deeper parts of the small intestine. Prolonged gastric residence of clavulanic acid caused by intragastric tablet deposition in the proximal stomach was identified as the reason for the decreased bioavailability of clavulanic acid after tablet intake following the meal.

Ertapenem clearance during modeled continuous renal replacement therapy.

PURPOSE: To determine ertapenem transmembrane clearance (CLtm) during continuous renal replacement therapy (CRRT) using a validated in vitro model. METHODS: Ertapenem clearance during continuous hemofiltration and hemodialysis was assessed with AN69 and polysulfone hemodiafilters at 4 dialysate (Qd) and ultrafiltration rates (Quf): 1, 2, 3, and 6 l/hour. Blood and dialysate samples were collected at each flow rate and assayed for urea (control solute) and ertapenem concentrations. The experiment was repeated 5 times for each hemodiafilter type. Ertapenem and urea sieving coefficient (SC) and saturation coefficient (SA) were assessed, and CLtm calculated. RESULTS: In continuous hemofiltration mode, urea and ertapenem SC ranged from 1.00 to 1.19 at all Quf and did not differ between hemodiafilter types. Consequently, convective CLtm also did not differ between hemodiafilters. In continuous dialysis mode, urea Cltm did not differ between hemodiafilter types at any Qd. However, ertapenem SA and CLtm were significantly different between hemodiafilter types at Qd 6l/hour (p<0.001). As Qd increased, mean +/- SD AN69 SA declined significantly from 0.87 +/- 0.12 at Qd 1 l/hour to 0.45 +/- 0.02 at Qd 6 l/hour (p<0.001). Ertapenem SA did not differ at any Qd with the polysulfone hemodiafilter (range 0.71-0.80). CONCLUSION: Ertapenem was cleared substantially in these in vitro CRRT models. However, our findings illustrate discordance between our observed SC and SA and the published unbound fraction of ertapenem. This finding has been reported with many other drugs, including carbapenem antibiotics. If in vivo studies corroborate our SA and SC findings, dosage adjustment for patients receiving CRRT will be required.

The effect of achiral calixarenes on chiral separation of propranolol-HCl and brompheniramine maleate in capillary electrophoresis using cyclodextrin as chiral selector.

In this study we have examined the effect of achiral water soluble p-sulfonatocalixarenes (SCX[n]) on chiral separation propranolol-HCl and brompheniramine maleate. Several cyclodextrins (CDs) and cyclodextrin derivatives were examined as chiral selectors applying complete filling technique (CFT) accompanied with the partial filling technique PFT of (SCX[n]) as achiral modifier. Only with hydroxypropyl-beta-cyclodextrin (HP-beta-CD) chiral separation could be achieved. The effect of the organic modifier on these chiral separations was examined. The results indicate that at pH 4.65, the use of HP-beta-CD (CFT) alone could not initiate chiral separations of both analytes and these chiral separations could be induced using HP-beta-CD (CFT) followed by SCX[n]/HP-beta-CD (PFT).

[Pharmacokinetics and pharmacodynamics of antibiotics in intensive care]. / Pharmakokinetik und Pharmakodynamik von Antibiotika in der Intensivmedizin.

Optimized dosage regimens of antibiotics have remained obscure since their introduction. During the last two decades pharmacokinetic(PK)-pharmacodynamic(PD) relationships, originally established in animal experiments, have been increasingly used in patients. The action of betalactams is believed to be governed by the time the plasma concentration is above the minimum inhibitory concentration (MIC). Aminoglycosides act as planned when the peak concentration is a multiple of the MIC and vancomycin seems to work best when the area under the plasma vs. time curve (AUC) to MIC has a certain ratio. Clinicians should be aware that these relationships can only be an indication in which direction dosing should go. Larger studies with sufficiently high numbers of patients and particularly severely sick patients are needed to prove the concepts. In times where all antibiotics can be measured with new technologies, the introduction of therapeutic drug monitoring (TDM) is suggested for ICUs (Intensive Care Unit). The idea of a central lab for TDM of antibiotics such as PEAK (Paul Ehrlich Antibiotika Konzentrationsmessung) is supported.

Population Modeling Integrating Pharmacokinetics, Pharmacodynamics, Pharmacogenetics, and Clinical Outcome in Patients With Sunitinib-Treated Cancer.

The tyrosine kinase inhibitor sunitinib is used as first-line therapy in patients with metastasized renal cell carcinoma (mRCC), given in fixed-dose regimens despite its high variability in pharmacokinetics (PKs). Interindividual variability of drug exposure may be responsible for differences in response. Therefore, dosing strategies based on pharmacokinetic/pharmacodynamic (PK/PD) models may be useful to optimize treatment. Plasma concentrations of sunitinib, its active metabolite SU12662, and the soluble vascular endothelial growth factor receptors sVEGFR-2 and sVEGFR-3, were measured in 26 patients with mRCC within the EuroTARGET project and 21 patients with metastasized colorectal cancer (mCRC) from the C-II-005 study. Based on these observations, PK/PD models with potential influence of genetic predictors were developed and linked to time-to-event (TTE) models. Baseline sVEGFR-2 levels were associated with clinical outcome in patients with mRCC, whereas active drug PKs seemed to be more predictive in patients with mCRC. The models provide the basis of PK/PD-guided strategies for the individualization of anti-angiogenic therapies.

Intravenous ciprofloxacin disposition in obesity.

The pharmacokinetics of ciprofloxacin and its metabolite 1 (desethyleneciprofloxacin) were studied in 17 obese men (mean age, 29.2 +/- 7.5 years; mean weight, 110.7 +/- 20.2 kg; mean body mass index, 36.4 +/- 3.9 kg/m2) and 11 control subjects (men of normal weight; mean age, 25.0 +/- 5.1 years; mean weight, 71.8 +/- 9.9 kg; mean body mass index, 23.3 +/- 2.4 kg/m2). Each subject received a single 400 mg intravenous dose of ciprofloxacin infused over 1 hour. Ciprofloxacin total clearance was significantly increased in obese subjects compared with control subjects (897.44 +/- 159.57 versus 744.44 +/- 120.51 ml/min, respectively; p < 0.05). Ciprofloxacin renal clearance in obese subjects (637.58 +/- 128.89 ml/min) was 29% higher than in control subjects (495.47 +/- 137.85 ml/min; p < 0.05). The elimination half-life values of ciprofloxacin and desethyleneciprofloxacin were not statistically different between groups. Ciprofloxacin steady-state volume of distribution (Vss) was significantly larger in obese group (269.17 +/- 51.64 versus 219.03 +/- 35.80 L; p < 0.01) compared with the control group, and when it was normalized by total body weight, obese subjects exhibited lower Vss/kg than control subjects (2.46 +/- 0.42 versus 3.06 +/- 0.31 L/kg; p < 0.001). These findings indicate that ciprofloxacin is distributed less to adipose tissue than to other tissues, but partial distribution to adipose tissue does occur. To normalize the volume of distribution of obese subjects to that of normal weight subjects, 45% of excess weight (total body weight minus ideal body weight) must be added to the ideal body weights of obese subjects.

Pharmacokinetics of gyrase inhibitors, Part 1: Basic chemistry and gastrointestinal disposition.

This review describes the physicochemistry and pharmacokinetic principles of gyrase inhibitors in relation to their distribution in the gastrointestinal tract. Their basicity and lipophilicity at physiologic pH, which affect their disposition in the gastrointestinal tract, are weakened or strengthened by substitutions on the quinoline nucleus. Heterocyclic substitution at position 7 significantly increases basicity and affects lipophilicity considerably. At physiologic pH, the 3-carboxyl group adds significant negative charge. The balance between the negatively charged carboxyl group and the positively charged heterocycle substitutions determines the pH-dependent ratio between ionized and un-ionized species and the solubility and lipophilicity of gyrase inhibitors. After oral administration, both the maximal plasma concentration (Cmax) and time to reach this value (Tmax) are affected primarily by the absorption constant. Absorption of N4'-methylated gyrase inhibitors tend to be greater than that of nonmethylated compounds. Acid-base properties affect absorption as do solubility and dissolution rates. Gyrase inhibitors probably are absorbed primarily in the upper gastrointestinal tract. Food does not alter overall absorption of several gyrase inhibitors studied but prolongs the Tmax slightly but significantly. N4'-methylation appears to protect against effects of food. Delay in gastric emptying may cause the increase in Tmax of gyrase inhibitors ingested with fatty meals. Effects of antacids on absorption of gyrase inhibitors depend on the interval between administration. Other ions also may reduce the absorption of gyrase inhibitors, but histamine-2 (H2)-antagonists appear to affect intestinal absorption of some, but not all, gyrase inhibitors. Gyrase inhibitors undergo significant gastrointestinal elimination.

Pharmacokinetics of gyrase inhibitors, Part 2: Renal and hepatic elimination pathways and drug interactions.

This article focuses on the relationship of the physicochemical properties of gyrase inhibitors to their hepatic and renal elimination pathways. Luminal fluid concentrations of gyrase inhibitors are affected by an active process and can be inhibited by agents such as probenecid that inhibit tubular secretion of anions. Probenecid may inhibit base transport in the proximal tubule and appears to inhibit base transport as well. Available data suggest that all gyrase inhibitors can be secreted as anions by the proximal tubules. Cimetidine, which is cationic at physiologic pH, inhibits base transport in the proximal tubule and appears to inhibit base transport of gyrase inhibitors. Reabsorption also affects tubular concentrations. Models that describe the effects of urinary flow and pH are discussed. The N4'-methylated derivatives are the most lipophilic, and addition or removal of the methyl group can, but does not always, affect reabsorption. The data indicate that all gyrase inhibitors undergo tubular secretion as either acids or bases and that some also are significantly reabsorbed. Hepatic handling and resultant excretion of metabolites are also influenced by the presence or absence of N4'-methylation. A step in the hepatic handling of N4'-methylated gyrase inhibitors that leads to N4'-oxidation has not yet been found in rufloxacin. Rebiotransformation of N4'-oxides was described in liver perfusion experiments. The potential for interaction with theophylline is not identical for all gyrase inhibitors. Enoxacin is the strongest inhibitor of theophylline and caffeine metabolism, followed by tosufloxacin, ciprofloxacin, and pefloxacin. Fleroxacin, ofloxacin, rufloxacin, and sparfloxacin have no or negligible effects. A likely mechanism for this interaction is the inhibition of subsets of the cytochrome P-450 enzyme. Structure activity relationships were established for this interaction. Piperazine ring-cleaved compounds and naphthyridine nuclei were shown to be most active inhibitors of cytochrome P-4501A2. The effect of various substituents was also tested, leading to an equation that predicts inhibition of 3-caffeine demethylation. Piperazine ring-cleaved compounds are more inhibitory than parent compounds, and a nitrogen at position 4 or 7, respectively, reduces or increases inhibitory activity. Data on interactions of rifampin and cyclosporine with gyrase inhibitors are conflicting. Rifampin increases the clearance of fleroxacin but does not change the elimination half-life significantly. Although norfloxacin may interfere with metabolism of the S enantiomer of warfarin, fleroxacin does not affect pharmacokinetics of either the R or S enantiomer or the anticoagulant response.(ABSTRACT TRUNCATED AT 400 WORDS)

Comparative pharmacokinetics of ciprofloxacin and temafloxacin in humans: a review.

Temafloxacin is a new antibacterial agent of the fluoroquinolone group. In comparison with ciprofloxacin, the current leading quinolone, temafloxacin shows higher and longer lasting plasma concentrations after equivalent doses due to an almost complete gastrointestinal absorption and a lower total clearance. Temafloxacin absorption is little influenced by food intake. Concomitant administration of antacids should be avoided; a time interval of at least 2 hours should elapse between intake of either quinolone and an antacid. Both quinolones are excreted mainly by the kidney. They differ in tubular secretion, which is high for ciprofloxacin and low for temafloxacin. The overall nonrenal elimination is similar for both compounds. Ciprofloxacin has a slightly higher extent of metabolism, while temafloxacin probably has a higher transintestinal elimination. The biliary excretion of both compounds is in the same range. The longer half-life of temafloxacin enables a once-daily dose regimen, whereas the usual recommended dosage of ciprofloxacin is twice daily. For both quinolones the apparent volumes of distribution per body weight are significantly above unity, indicating good tissue penetration with intracellular uptake. The concentrations in the extracellular fluids are directly related to the corresponding plasma concentrations. The penetration of temafloxacin into the body fluids investigated--tears, nasal secretion, saliva, sweat, prostatic and seminal fluid--in general exceeds that of ciprofloxacin (with the exception of seminal fluid). Unlike ciprofloxacin, there is no drug interaction with methylxanthines. Comparative clinical studies reflecting the complex interrelating factors of host and pathogens are needed to demonstrate the significance of the pharmacokinetic differences between temafloxacin and ciprofloxacin.

Pharmacokinetics of temafloxacin in patients with liver impairment.

A multicentre study was conducted to determine whether liver impairment would alter the pharmacokinetics of temafloxacin, a new fluoroquinolone antimicrobial agent. 16 patients with cirrhosis and 12 healthy volunteers (the control group) received a single oral 600mg dose of temafloxacin. Blood and urine were sampled at frequent intervals after drug administration and assayed by high performance liquid chromatography. The mean age of patients with liver impairment was greater than that of the control group; they also had a lower creatinine clearance and urine output. There was no difference between the groups in either the peak plasma temafloxacin concentration or the time to reach peak concentration. However, the volume of distribution and elimination rate constant of temafloxacin were significantly lower in the group with liver impairment, as were total temafloxacin clearance, renal clearance, and the ratio of renal:creatinine clearance. Nonrenal clearance was similar in patients and controls. Creatinine clearance and urine output were found to account for most of the intersubject variability in total clearance as determined by multiple linear regression analysis. Because the altered temafloxacin pharmacokinetics appear to be primarily due to impaired renal function, this should be the main determinant of temafloxacin dosage in patients with liver disease.