Pharmacokinetics of grepafloxacin after oral administration of single and repeat doses in healthy young males

Pharmacokinetics and Pharmacodynamics of the New Quinolones

In this review, the authors describe the pharmacokinetic (PK) and pharmacodynamic (PD) characteristics of the new quinolones (levofloxacin, gatifloxacin, moxifloxacin, gemifloxacin, and garenoxacin) and discuss their implications on adequate therapy of patients with respiratory infections. The newer quinolones display excellent bioavailability and have longer serum half-lives than ciprofloxacin. In addition, they have the ability to concentrate in respiratory tract tissues and fluids at levels that exceed serum-drug concentrations. Also, the newer quinolones exhibit broad-spectrum activity against both susceptible and resistant organisms. Those favorable PK/PD properties make the new quinolones an attractive therapeutic alternative to traditional agents for common respiratory infections. Understanding the PK/PD of quinolone antibiotics can facilitate selection of optimal regimens to hasten response, prevent treatment failures, and minimize the development of resistance.

Fluoroquinolone disposition: identification of the contribution of renal secretory and reabsorptive drug transporters

INTRODUCTION

Fluoroquinolones (FQs) exist as charged molecules in blood and urine making their absorption, distribution, and elimination likely to be influenced by active transport mechanisms. Greater understanding of in vivo FQ clearance mechanisms should help improve the predictability of drug-drug interactions, enhance the clinical safety and efficacy, and aid future novel drug design strategies.

AREAS COVERED

The authors present an overview of FQ development and associated drug-drug interactions, followed by systematic quantitative review of the physicochemical and in vivo pharmacokinetic properties for 15 representative FQs using historical clinical literature. These results were correlated with in vitro studies implicating drug transporters in FQ clearance to link clinical and in vitro evidence supporting the contribution of drug transport mechanisms to FQ disposition. Specific transporters likely to handle FQs in human renal proximal tubule cells are also identified.

EXPERT OPINION

Renal handling, that is, tubular secretion and reabsorption, appears to be the main determinant of FQ plasma half-life, clinical duration of action, and drug-drug interactions. Due to their zwitterionic nature, FQs are likely to interact with organic anion and cation transporters within the solute carrier (SLC) superfamily, including OAT1, OAT3, OCT2, OCTN1, OCTN2, MATE1, and MATE2. The ATP-binding cassette (ABC) transporters MDR1, MRP2, MRP4, and BCRP also may interact with FQs.

Antistaphylococcal effect related to the area under the curve/MIC ratio in an in vitro dynamic model: predicted breakpoints versus clinically achievable values for seven fluoroquinolones

Prediction of the relative efficacies of different fluoroquinolones is often based on the ratios of the clinically achievable area under the concentration-time curve (AUC) to the MIC, usually with incorporation of the MIC50 or the MIC90 and with the assumption of antibiotic-independent patterns of the AUC/MIC-response relationships. To ascertain whether this assumption is correct, the pharmacodynamics of seven pharmacokinetically different quinolones against two clinical isolates of Staphylococcus aureus were studied by using an in vitro model. Two differentially susceptible clinical isolates of S. aureus were exposed to two 12-h doses of ciprofloxacin (CIP) and one dose of gatifloxacin (GAT), gemifloxacin (GEM), grepafloxacin (GRX), levofloxacin (LVX), moxifloxacin (MXF), and trovafloxacin (TVA) over similar AUC/MIC ranges from 58 to 932 h. A specific bacterial strain-independent AUC/MIC relationship with the antimicrobial effect (I(E)) was associated with each quinolone. Based on the I(E)-log AUC/MIC relationships, breakpoints (BPs) that are equivalent to a CIP AUC/MIC ratio of 125 h were predicted for GRX, MXF, and TVA (75 to 78 h), GAT and GEM (95 to 103 h) and LVX (115 h). With GRX and LVX, the predicted BPs were close to those established in clinical settings (no clinical data on other quinolones are available in the literature). To determine if the predicted AUC/MIC BPs are achievable at clinical doses, i.e., at the therapeutic AUCs (AUC(ther)s), the AUC(ther)/MIC50 ratios were studied. These ratios exceeded the BPs for GAT, GEM, GRX, MXF, TVA, and LVX (750 mg) but not for CIP and LVX (500 mg). AUC/MIC ratios above the BPs can be considered of therapeutic potential for the quinolones. The highest ratios of AUC(ther)/MIC50 to BP were achieved with TVA, MXF, and GEM (2.5 to 3.0); intermediate ratios (1.5 to 1.6) were achieved with GAT and GRX; and minimal ratios (0.3 to 1.2) were achieved with CIP and LVX.

Grepafloxacin: an overview of antibacterial activity, pharmacokinetics, clinical efficacy and safety

The treatment of respiratory tract infection is the most common reason for antibiotic prescribing. However, therapeutic options are diminishing as antibiotic resistance to penicillins and macrolides in key respiratory pathogens is increasing. As resistance increases, there are parallel rises in the number of treatment failures and the total cost of infection management. New generation broad-spectrum fluoroquinolones, such as grepafloxacin, have recently been recommended as a first-line treatment option in guidelines for lower respiratory tract infection. Grepafloxacin is an oral fluoroquinolone, with a microbiological and clinical profile that is particularly suited to the treatment of community-acquired respiratory infections. In vitro, it is rapidly bactericidal, and compared with earlier quinolones, its broad spectrum activity encompasses all important respiratory pathogens; Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, Mycoplasma pneumoniae, Chlamydia pneumoniae and Legionella pneumophila, including strains which are resistant to penicillin, other beta-lactam antibiotics and macrolides. In addition, grepafloxacin achieves high lung concentrations, and its long half-life (up to 15 h) enables once daily dosing. Overall, grepafloxacin combines the positive properties of the beta-lactam antibiotics against conventional Gram-positive and Gram-negative respiratory pathogens, with the activity of the macrolides against atypical pathogens. In patients with bacteriologically documented infections, clinical studies in community-acquired pneumonia have shown that treatment for 7-10 days once daily (o.d.) with approximately 600 mg is equivalent to that with either twice daily (b.i.d.) clarithromycin 250 mg, or three times daily (t.i.d.) cefaclor 500 mg, and superior to that with t.i.d. amoxycillin 500 mg. In these studies, grepafloxacin proved effective in the treatment of both typical and atypical pneumonia. In acute bacterial exacerbations of chronic bronchitis (ABECB), 7-10 days treatment with o.d. grepafloxacin 400 mg or 600 mg has been shown to be equivalent to that with either t.i.d. amoxycillin 500 mg, or b.i.d. ciprofloxacin 500 mg. In patients with a documented bacterial pathogen, microbiological success with both grepafloxacin dosage regimens was superior to amoxycillin 500 mg t.i.d. In addition, short course treatment of ABECB with 400 mg of grepafloxacin given o.d. for five days has been shown to be as effective, clinically and microbiologically as a ten-day course of the same dose. The safety profile of grepafloxacin has been well-characterised from data from over 12,000 patients treated in Phase II/III and post-marketing studies, and over 400,000 patients treated worldwide in routine clinical practice. The most commonly reported adverse events are gastrointestinal, mainly nausea and unpleasant taste. The potential for photosensitivity and central nervous system effects is low, and there have been no reports of convulsions. No unique or unexpected.

The activity of grepafloxacin in two murine models of Mycobacterium avium infection

The activity against Mycobacterium avium complex (MAC) of varying doses of grepafloxacin (GRE; 25 mg/kg, 50 mg/kg, 100 mg/kg, and 200 mg/kg) were compared to clarithromycin (CLA; 100 mg/kg and 200 mg/kg), ethambutol (EMB; 100 mg/kg), and rifabutin (RBT; 10 mg/kg) using an intranasal (IN) infection model compared to an intravenous (IV) infection model. Beige mice (C57BL6/J-Lyst bg J/+) were infected intranasally with about 10(6) organisms and for the IV model about 10(7) organisms. Treatment for both models was started 1 week postinfection and given by gavage 5 days/week for 4 weeks. At the initiation of therapy, an early control group was killed to determine the initial organism load. Three days following the completion of therapy, drug-treated groups of mice and the late control group were killed and the response to therapy measured. The most effective agents were CLA and RBT. GRE and EMB had modest activities in both the IN and the IV models. A matched comparison between IN and IV challenges for each of the agents used revealed greater suppression of MAC in the IN model compared to the IV model.

Limited Influence of P‐Glycoprotein on Small‐Intestinal Absorption of Cilostazol, a High Absorptive Permeability Drug

Intestinal transport of the type III phosphodiesterase inhibitor cilostazol was characterized to evaluate the influence of secretory transporter. Intestinal absorption of cilostazol measured by the in situ closed loop method, showed regional differences, with high permeability in the upper part of the small intestine. Intestinal secretory transport of cilostazol at the ileum was tended to be decreased by the increase of tested concentration of cilostazol from 10 to 20 microM when evaluated by means of a Ussing-type chamber method with mounted rat intestinal tissues. Transcellular transport of cilostazol in the basolateral-to-apical direction in LLC-GA5-COL150 cells, which overexpress P-glycoprotein, was higher than that in parental LLC-PK1 cells. In addition, cilostazol reduced the basolateral-to-apical transport and increased the accumulation of [(3)H]daunomycin in LLC-GA5-COL150 cells. Accordingly, cilostazol was demonstrated to be transported by P-glycoprotein, while cilostazol is not likely to cause induction of the expression level of P-glycoprotein by the same manner with rifampin. Apical-to-basolateral transport of cilostazol in Caco-2 cells was increased in a low concentration range, followed by a decrease with further increase of the concentration, while the permeability coefficient of cilostazol was above 1 x 10(-6) cm/s at any concentration. Initial uptake of [(14)C]cilostazol by Caco-2 cells was temperature dependent and was reduced in the presence of unlabeled cilostazol, suggesting that apical uptake is also mediated by a transporter(s). In conclusion, intestinal absorption of cilostazol, which has a high absorptive permeability, may not be significantly hampered by efflux transporters, such as P-glycoprotein.

Multiple-dose safety and pharmacokinetics of oral garenoxacin in healthy subjects

Garenoxacin (T-3811ME, BMS-284756) is a novel des-F(6) quinolone that has been shown to be effective in vitro against a wide range of clinically important pathogens, including gram-positive and gram-negative aerobes and anaerobes. This study was conducted to evaluate the safety and tolerability of multiple oral doses (100 to 1200 mg/day) of garenoxacin in healthy subjects and to determine its multiple-dose pharmacokinetics. Forty healthy male and female subjects (18 to 45 years of age) were enrolled in this randomized, double-blind, placebo-controlled, sequential, multiple- and ascending-dose study. Each subject received a once-daily oral dose of garenoxacin (100, 200, 400, 800, or 1200 mg) or a placebo for 14 days. Blood and urine samples were collected for measurements of garenoxacin by validated liquid chromatography with dual mass spectrometry, and plasma garenoxacin concentration-time data were analyzed by noncompartmental methods. The effects of garenoxacin on Helicobacter pylori, psychometric test performance, and electrocardiograms were assessed, as was drug safety. Over the 14 days of dosing, geometric mean peak concentrations of garenoxacin in plasma (C(max)) at the 100- and 1200-mg doses were within the ranges of 1.2 to 1.6 and 16.3 to 24 microg/ml, respectively. The corresponding values for the geometric mean area under the concentration-time curve over the dosing interval (AUC(tau)) for garenoxacin in plasma at the 100- and 1200-mg doses were within the ranges of 11.5 to 15.7 and 180 to 307 microg. h/ml, respectively. Increases in systemic exposure to garenoxacin in terms of AUC and C(max) were approximately dose proportional over the 100- to 400-mg dose range but demonstrated increases that were somewhat greater than the dose increments at the 800- and 1200-mg doses. Median values for the time to achieve C(max) were in the range of 1.13 to 2.50 h for all doses. The mean elimination half-life for garenoxacin in plasma appeared to be independent of dose and ranged from 13.3 to 17.8 h (day 14). Approximately 30 to 50% of an administered garenoxacin dose was excreted unchanged in the urine. At doses of 100 to 400 mg, steady-state concentrations of garenoxacin in plasma appeared to be attained by the fourth dose. Multiple oral doses of garenoxacin were well tolerated and did not demonstrate clinically significant effects on QT(c) or psychometric test results. Garenoxacin administered alone for 14 days at doses of >or=400 mg demonstrated activity against H. pylori. These results suggest that multiple once-daily oral doses of garenoxacin of up to 1200 mg are safe and well tolerated and that the pharmacokinetics of garenoxacin support once-daily administration.

Determination of lipophilicity of two quinolone antibacterials, ciprofloxacin and grepafloxacin, in the protonation equilibrium

The objective of this study was to compare protonation equilibrium and lipophilicity of two quinolone antibacterials, grepafloxacin (GPFX) and ciprofloxacin (CPFX), in order to give an insight into effects on the physicochemical properties by slight structural motifs. The protonation equilibrium was investigated by a spectrophotometry. Macro- and micro-dissociation constants were simultaneously determined, based on nonlinear regression analysis using the MULTI program, and then microspecies distribution could be described accordingly. Zwitterionic microspecies predominated at isoelectrical point (pI) for both drugs, and the concentration ratio of neutral to zwitterionic forms was near 4-fold greater for GPFX than that for CPFX. The apparent partition coefficient (D(O/B,pH)) versus pH profiles had the shape of a parabolic curve in an n-octanol/buffer system, and reached the maximum around pI for both, respectively. Moreover, two introduced methyl groups in GPFX increased not only intrinsic lipophilicity but also neutral microspecies fraction relative to CPFX, and D(O/B,pH) of GPFX was consequently far higher than that of CPFX. The results emphasized that there were significant differences in protonation equilibrium and lipophilicity between GPFX and CPFX, which conduced to explaining their different behavior in terms of antibacterial activities and pharmacokinetics.

Commonly used antibacterial and antifungal agents for hospitalised paediatric patients: implications for therapy with an emphasis on clinical pharmacokinetics

Due to normal growth and development, hospitalised paediatric patients with infection require unique consideration of immune function and drug disposition. Specifically, antibacterial and antifungal pharmacokinetics are influenced by volume of distribution, drug binding and elimination, which are a reflection of changing extracellular fluid volume, quantity and quality of plasma proteins, and renal and hepatic function. However, there is a paucity of data in paediatric patients addressing these issues and many empiric treatment practices are based on adult data. The penicillins and cephalosporins continue to be a mainstay of therapy because of their broad spectrum of activity, clinical efficacy and favourable tolerability profile. These antibacterials rapidly reach peak serum concentrations and readily diffuse into body tissues. Good penetration into the cerebrospinal fluid (CSF) has made the third-generation cephalosporins the agents of choice for the treatment of bacterial meningitis. These drugs are excreted primarily by the kidney. The carbapenems are broad-spectrum beta-lactam antibacterials which can potentially replace combination regimens. Vancomycin is a glycopeptide antibacterial with gram-positive activity useful for the treatment of resistant infections, or for those patients allergic to penicillins and cephalosporins. Volume of distribution is affected by age, gender, and bodyweight. It diffuses well across serous membranes and inflamed meninges. Vancomycin is excreted by the kidneys and is not removed by dialysis. The aminoglycosides continue to serve a useful role in the treatment of gram-negative, enterococcal and mycobacterial infections. Their volume of distribution approximates extracellular space. These drugs are also excreted renally and are removed by haemodialysis. Passage across the blood-brain barrier is poor, even in the face of meningeal inflammation. Low pH found in abscess conditions impairs function. Toxicity needs to be considered. Macrolide antibacterials are frequently used in the treatment of respiratory infections. Parenteral erythromycin can cause phlebitis, which limits its use. Parenteral azithromycin is better tolerated but paediatric pharmacokinetic data are lacking. Clindamycin is frequently used when anaerobic infections are suspected. Good oral absorption makes it a good choice for step-down therapy in intra-abdominal and skeletal infections. The use of quinolones in paediatrics has been restricted and most information available is in cystic fibrosis patients. High oral bioavailability is also important for step-down therapy. Amphotericin B has been the cornerstone of antifungal treatment in hospitalised patients. Its metabolism is poorly understood. The half-life increases with time and can be as long as 15 days after prolonged therapy. Oral absorption is poor. The azole antifungals are being used increasingly. Fluconazole is well tolerated, with high bioavailability and good penetration into the CSF. Itraconazole has greater activity against aspergillus, blastomycosis, histoplasmosis and sporotrichosis, although it's pharmacological and toxicity profiles are not as favourable.

Pharmacokinetic role of P-glycoprotein in oral bioavailability and intestinal secretion of grepafloxacin in vivo

The purpose of this study was to clarify the contribution of P-glycoprotein to the bioavailability and intestinal secretion of grepafloxacin and levofloxacin in vivo. Plasma concentrations of grepafloxacin and levofloxacin after intravenous and intraintestinal administration were increased by cyclosporin A, a P-glycoprotein inhibitor, in rats. The total body clearance and volume of distribution at steady state of grepafloxacin were significantly decreased to 60 and 63% of the corresponding control values by cyclosporin A. The apparent oral clearance of grepafloxacin was decreased to 33% of the control, and the bioavailability of grepafloxacin was increased to 95% by cyclosporin A from 53% in the controls. Intestinal clearance of grepafloxacin and levofloxacin were decreased to one-half and one-third of the control, respectively, and biliary clearance of grepafloxacin was also decreased to one-third with cyclosporin A in rats. Intestinal secretion of grepafloxacin in mdr1a/1b (-/-) mice, which lack mdr1-type P-glycoproteins, was significantly decreased compared with wild-type mice, although the biliary secretion was similar. Intestinal secretion of grepafloxacin in wild-type mice treated with cyclosporin A was comparable to those in mdr1a/1b (-/-) mice with or without cyclosporin A, indicating that cyclosporin A completely inhibited P-glycoprotein-mediated intestinal transport of grepafloxacin. In conclusion, our results indicated that P-glycoprotein mediated the intestinal secretion of grepafloxacin and limited the bioavailability of this drug in vivo.

Application of terbium-sensitized luminescence for the determination of grepafloxacin in human urine and serum

Analytical performance and applications of a selective and sensitive lanthanide-sensitized luminescence method for the determination of grepafloxacin is described. The method is based in the time-resolved luminescence signal from a terbium (III)-grepafloxacin complex in a micellar solution of sodium dodecyl sulfate. The optimized method allows the determination of 10-500 ng mL(-1) of grepafloxacin in 7.5 mM sodium dodecyl sulfate solution containing 0.16 M acetic acid-sodium acetate buffer (pH 6.0) and 7.5 mM Na(2)SO(3) (chemical deoxygenation agent), with lambda(exc) = 275 nm and lambda(em) = 546 nm. Grepafloxacin was determined in human serum (by external calibration method) and urine (by standard additions method), spiked at levels found after drug administration at normal clinical doses. Average recoveries found were 89.6 (relative standard deviation 0.9%) and 102 (relative standard deviation 2%), respectively.

Pharmacokinetics, safety and tolerability of moxifloxacin, a novel 8-methoxyfluoroquinolone, after repeated oral administration

OBJECTIVE

To investigate the pharmacokinetics, safety and tolerability of moxifloxacin after single and repeated doses.

DESIGN AND SETTING

This series comprised 3 separate placebo-controlled studies, 2 studies with a randomised crossover design (up to 400 mg/day) and 1 study with a group comparison design (600mg once daily).

PATIENTS AND PARTICIPANTS

Healthy male volunteers were included in these studies.

METHODS

Participants received 5-day treatment courses of moxifloxacin 100mg (n = 8) or 200mg (n = 8) twice daily or 400mg once daily (n = 7), or a 10-day treatment course of moxifloxacin 600mg once daily (n = 7). Pharmacokinetics were characterised after the first dose (24-hour profile) and the last dose (96-hour profile), with additional trough and peak measurements during the courses.

RESULTS

All treatments were well tolerated. No clinically relevant changes in the standard laboratory tests, vital signs or ECG were observed. Minimum plasma concentrations required to inhibit 90% of susceptible micro-organisms (e.g. 0.125 mg/L for Streptococcus pneumoniae) were attained rapidly and exceeded until the end of treatment. Repeated doses of 100 and 200mg twice daily and 400mg once daily resulted in stable trough and peak concentrations within 3 days of the first dose. The concentrations at steady state were moderately higher (approximately 30% for 400mg once daily) than after the first dose. Steady-state peak concentrations were between 0.9 mg/L (100mg twice daily) and 5.7 mg/L (600mg once daily). The terminal elimination half-life was 14 to 15 hours, supporting once daily administration of the drug. Accumulation ratios ranged between 87% for the lowest dosage and 111% after repeated doses of 600mg once daily, indicating the absence of clinically relevant accumulation due to non-linear pharmacokinetics. Across the studies, the average exposure after single and repeated doses was proportional to the dose administered.

CONCLUSIONS

These studies indicate that, based on the safety profile and the pharmacokinetic behaviour of moxifloxacin, a dosage regimen of 400mg given once daily should be effective and well tolerated for the treatment of various infections.

Crossover assessment of serum bactericidal activity of grepafloxacin, ofloxacin and clarithromycin against respiratory pathogens after oral administration to healthy volunteers

Serum bactericidal activity was studied in a crossover manner in 10 volunteers, after 2-day administration of grepafloxacin 600 mg qd, ofloxacin 400 mg bid and clarithromycin 500 mg bid. Bactericidal activity against clinical isolates of Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis and Klebsiella pneumoniae, was estimated using a standardized microdilution method. Grepafloxacin was highly active against Gram-negative organisms and adequate against pneumococci (mean, 1:13.3). Clarithromycin was very active against both penicillin-susceptible and penicillin-partially-resistant S. pneumoniae (1:102.5) but had poor activity against H. influenzae (1:3.1). Minor adverse effects were commonly associated with grepafloxacin.

Grepafloxacin pharmacokinetics in individuals with hepatic dysfunction

The pharmacokinetics of grepafloxacin, a new broad spectrum fluoroquinolone antibiotic, were studied in 2 trials involving 14 healthy volunteers, 10 individuals with mild (Child-Pugh Class A) impairment of liver function, and 12 with moderate (Child-Pugh Class B or C) hepatic impairment. All participants received an oral dose of grepafloxacin 400 mg, daily for 7 days, and plasma and urine grepafloxacin concentrations were measured over 7 days. The pooled data from participants with impaired liver function showed that, compared with healthy individuals, peak plasma grepafloxacin concentrations, area under the plasma concentration-time curve and proportion of the dose excreted in the urine were increased. In addition, apparent total clearance was reduced in the presence of hepatic dysfunction. Peak concentrations were increased by 36% and 48% in individuals with Class A and B disease, respectively; the corresponding reductions in clearance were 33% and 55%, respectively. Child-Pugh scores and components of the scores showed no correlation with any pharmacokinetic variables. Based on these findings, we recommend a daily grepafloxacin dose of 400 mg in patients with mild hepatic impairment, irrespective of the severity of infection. Grepafloxacin should not be used in patients with moderate or severe liver disease.

Effects of sparfloxacin, grepafloxacin, moxifloxacin, and ciprofloxacin on cardiac action potential duration

Fluoroquinolone antibiotics have been associated with QT prolongation following administration to humans. This study compares the effects of four fluoroquinolones, sparfloxacin, grepafloxacin, moxifloxacin and ciprofloxacin on action potential duration recorded from canine isolated cardiac Purkinje fibres. Left and right ventricular Purkinje fibres were isolated from canine hearts and continuously superfused with physiological salt solution. Action potential duration at 90% repolarization was recorded via intracellular microelectrodes. Sparfloxacin, grepafloxacin, moxifloxacin and ciprofloxacin prolonged action potential duration in a concentration dependent manner. Mean concentrations causing a 15% prolongation of action potential duration recorded at a stimulation frequency of 1 Hz were: sparfloxacin 4.2+/-0.7 microg/ml; grepafloxacin 9.3+/-0.9 microg/ml; moxifloxacin 9.9+/-1.6 microg/ml and ciprofloxacin 72.8+/-26.4 microg/ml. Prolongation was inverse frequency dependent with larger increases in action potential duration occurring when the stimulation frequency was reduced to 0.5 Hz. These results indicate that effects on action potential duration vary within this class of compound. Rank order of potency was sparfloxacin > grepafloxacin = moxifloxacin > ciprofloxacin.

Determination of grepafloxacin in plasma and urine by a simple and rapid high-performance liquid chromatographic method

A rapid, specific, sensitive and economical method has been developed and validated for the determination of grepafloxacin in human plasma and urine. The assay consisted of reversed-phase HPLC with UV detection. Plasma proteins were removed by a fast and efficient procedure that has eliminated the need for costly extraction and evaporation. For the urine samples, the only required sample preparation was dilution. Separation was achieved on a reversed-phase TSK gel column with an isocratic mobile system. The method had a quantification limit of 0.05 microg/ml in plasma and 0.5 microg/ml in urine. The coefficients of variation (C.V.) were less than 4% for within- and between-day analyses. The method was successfully applied to a pharmacokinetic study, and was proved to be simple, fast and reproducible.

Comparison of the fluoroquinolones based on pharmacokinetic and pharmacodynamic parameters

Assessment of pharmacodynamic activity from standard in vitro minimum inhibitory concentrations (MICs) alone is insufficient to predict in vivo potency. Achievable serum and tissue concentrations as well as pharmacokinetic characteristics must be considered. When pharmacokinetic and pharmacodynamic values are combined, the area under the inhibitory curve (AUIC) and peak concentration:MIC ratio predict clinical cure for fluoroquinolones. Clinical data and animal models indicate that a peak:MIC of 10:1 and above and an AUIC of 125 and above are predictive of a clinical cure for this class of antimicrobials against gram-negative organisms. The values may be used to compare and contrast fluoroquinolones to determine which would be best for treating a specific microorganism. Pharmacodynamic data also can be used to design regimens that minimize the risk of suboptimal drug levels. Ensuring the optimal fluoroquinolone dosage based on pharmacodynamic principles would diminish the emergence of resistant organisms and prevent treatment failures.

Postantibiotic effects of grepafloxacin compared to those of five other agents against 12 gram-positive and -negative bacteria

The postantibiotic effect (PAE) (10x the MIC) and the postantibiotic sub-MIC effects (0.125, 0.25, and 0.5x the MIC) were determined for six compounds against 12 strains. Measurable PAEs ranged between 0 and 1.8 h for grepafloxacin, 0 and 2.2 h for ciprofloxacin, 0 and 3. 1 h for levofloxacin, 0 and 2.2 h for sparfloxacin, 0 and 2.4 h for amoxicillin-clavulanate and 0 and 4.8 h for clarithromycin. Reexposure to subinhibitory concentrations increased the PAEs against some strains.

Effects of liver disease on pharmacokinetics. An update

Liver disease can modify the kinetics of drugs biotransformed by the liver. This review updates recent developments in this field, with particular emphasis on cytochrome P450 (CYP). CYP is a rapidly expanding area in clinical pharmacology. The information currently available on specific isoforms involved in drug metabolism has increased tremendously over the latest years, but knowledge remains incomplete. Studies on the effects of liver disease on specific isoenzymes of CYP have shown that some isoforms are more susceptible than others to liver disease. A detailed knowledge of the particular isoenzyme involved in the metabolism of a drug and the impact of liver disease on that enzyme can provide a rational basis for dosage adjustment in patients with hepatic impairment. The capacity of the liver to metabolise drugs depends on hepatic blood flow and liver enzyme activity, both of which can be affected by liver disease. In addition, liver failure can influence the binding of a drug to plasma proteins. These changes can occur alone or in combination; when they coexist their effect on drug kinetics is synergistic, not simply additive. The kinetics of drugs with a low hepatic extraction are sensitive to hepatic failure rather than to liver blood flow changes, but drugs having a significant first-pass effect are sensitive to alterations in hepatic blood flow. The drugs examined in this review are: cardiovascular agents (angiotensin converting enzyme inhibitors, angiotensin II receptor antagonists, calcium antagonists, ketanserin, antiarrhythmics and hypolipidaemics), diuretics (torasemide), psychoactive and anticonvulsant agents (benzodiazepines, flumazenil, antidepressants and tiagabine), antiemetics (metoclopramide and serotonin antagonists), antiulcers (acid pump inhibitors), anti-infectives and antiretroviral agents (grepafloxacin, ornidazole, pefloxacin, stavudine and zidovudine), immunosuppressants (cyclosporin and tacrolimus), naltrexone, tolcapone and toremifene. According to the available data, the kinetics of many drugs are altered by liver disease to an extent that requires dosage adjustment; the problem is to quantify the required changes. Obviously, this requires the evaluation of the degree of hepatic impairment. At present there is no satisfactory test that gives a quantitative measure of liver function and its impairment. A critical evaluation of these methods is provided. Guidelines providing a rational basis for dosage adjustment are illustrated. Finally, it is important to consider that liver disease not only affects pharmacokinetics but also pharmacodynamics. This review also examines drugs with altered pharmacodynamics.

The new fluoroquinolones: A critical review

OBJECTIVE

This paper reviews the literature available on the new fluoroquinolones - clinafloxacin, gatifloxacin, grepafloxacin, levofloxacin, moxifloxacin, sparfloxacin and trovafloxacin - to compare these agents with each other and contrast them with ciprofloxacin, an older fluoroquinolone.

DATA SELECTION

Published papers used were obtained by searching MEDLINE for articles published between 1994 and 1998, inclusive. References of published papers were also obtained and reviewed. Abstracts from scientific proceedings were reviewed.

DATA EXTRACTION

Due to the limited data available on several of the agents, criteria for study inclusion in the in vitro, pharmacokinetics and in vivo sections were not restrictive.

DATA SYNTHESIS

The new fluoroquinolones offer excellent Gram-negative bacillary activity and improved Gram-positive activity (eg, against Streptococcus pneumoniae and Staphylococcus aureus) over ciprofloxacin. Clinafloxacin, gatifloxacin, moxifloxacin, sparfloxacin and trovafloxacin display improved activity against anaerobes (eg, Bacteriodes fragilis). All of the new fluoroquinolones have a longer serum half-life than ciprofloxacin (allowing for once daily dosing), and several are eliminated predominantly by nonrenal means. No clinical trials are available comparing the new fluoroquinolones with each other. Clinical trials comparing the new fluoroquinolones with standard therapy have demonstrated good efficacy in a variety of infections. Their adverse effect profile is similar to that of ciprofloxacin. Clinafloxacin and sparfloxacin cause a high incidence of phototoxicity (1.5% to 14% and 2% to 11.7%, respectively), grepafloxacin causes a high incidence of taste perversion (9% to 17%) and trovafloxacin causes a high incidence of dizziness (11%). They all interact with metal ion-containing drugs (eg, antacids), and clinafloxacin and grepafloxacin interact with theophylline. The new fluoroquinolones are expensive; however, their use may result in savings in situations where, because of their potent and broad spectrum of activity, they can be used orally in place of intravenous antibiotics.

CONCLUSIONS

The new fluoroquinolones offer advantages over ciprofloxacin in terms of improved in vitro activity and pharmacokinetics. Whether these advantages translate into improved clinical outcomes is presently unknown. The new fluoroquinolones have the potential to emerge as important therapeutic agents in the treatment of respiratory tract and genitourinary tract infections.

Effectiveness of short-course therapy (5 days) with grepafloxacin in the treatment of acute bacterial exacerbations of chronic bronchitis

Three hundred eighty-nine patients were enrolled in a double-masked, multicenter, randomized clinical trial comparing the clinical and bacteriologic efficacies and safety of a 5-day course (n = 195) versus a 10-day course (n = 194) of grepafloxacin 400 mg once daily in the treatment of acute bacterial exacerbations of chronic bronchitis (ABECB). Patients in the 5-day treatment group received placebo on days 6 through 10. Bacteriologic assessments were based on cultures of sputum specimens obtained before and, when possible, during and after treatment. Organisms were isolated from the pretreatment sputum specimens of 332 of 388 (86%) patients, the primary pathogens being Haemophilus parainfluenzae, Haemophilus influenzae, Streptococcus pneumoniae, Moraxella catarrhalis, and Staphylococcus aureus (29%, 19%, 4%, 5%, and 5% of isolates, respectively). Among isolates tested for beta-lactamase production, results were positive in 25% of H influenzae isolates and 90% of M catarrhalis isolates. Forty-two percent of S pneumoniae isolates demonstrated reduced susceptibility (intermediate or high-level resistance) to penicillin. A satisfactory clinical outcome (cure or improvement) was achieved in 83% (128 of 155) and 81% (122 of 150) of clinically evaluable patients treated with grepafloxacin for 5 or 10 days, respectively. Pathogens were eradicated or presumed eradicated in 77% (106 of 138) and 80% (98 of 123) of bacteriologically evaluable patients treated with grepafloxacin for 5 or 10 days, respectively. The 2 treatment groups were equivalent with respect to both clinical and bacteriologic efficacy, and no statistically significant differences in the incidence of drug-related adverse events were seen between the 2 groups. Substantial symptom relief was evident with both treatment regimens by the first during-treatment measurement, which occurred between days 3 through 5. These results indicate that treatment with 400 mg grepafloxacin once daily for 5 days is as well tolerated and effective as treatment for 10 days in patients with ABECB. The lower cost compared with a 10-day regimen and the increased likelihood that patients will complete the entire shorter, once-daily regimen make the 5-day grepafloxacin regimen a useful therapeutic option in the treatment of ABECB.

Grepafloxacin: a review of its safety profile based on clinical trials and postmarketing surveillance

The safety profile of grepafloxacin has been characterized in a number of preclinical and clinical studies. Preclinical investigations have shown that its toxicologic profile is similar to that of other fluoroquinolones, and phase I studies in humans have confirmed these data. A photosensitivity study demonstrated equivalence with ciprofloxacin, and a study in elderly patients taking the highest clinical dose of grepafloxacin indicated that prolongation of the QTc interval by grepafloxacin was less than 2 ms, 15 times less than that observed in a study of erythromycin. In phase II and III clinical investigations conducted in the United States and the United Kingdom, safety data have been gathered from more than 3000 patients with either community-acquired pneumonia or acute bacterial exacerbations of chronic bronchitis. The most common adverse events with grepafloxacin 400 or 600 mg were gastrointestinal, such as nausea, vomiting, and diarrhea. The frequency of these adverse events was similar to that seen with ciprofloxacin. Significantly more patients reported a mild, unpleasant metallic taste with grepafloxacin than with ciprofloxacin, but <1% of patients withdrew from therapy because of this. Headache was observed significantly more often in ciprofloxacin-treated patients than in grepafloxacin-treated patients. Recent postmarketing data confirm the good tolerability and safety profile of grepafloxacin. These data, from a case-report study of more than 9000 patients in Germany, demonstrated that only 2.3% of patients reported adverse events when grepafloxacin was used in routine clinical practice. The most frequently reported events were nausea (0.8%) and gastrointestinal symptoms (0.4%). Dizziness was reported by only 0.3% of patients, and only 4 patients (0.04%) reported photosensitization. Adverse events did not appear to be either dose dependent or related to diagnosis. More than 400,000 patients world-wide have received grepafloxacin treatment. No new safety issues have arisen from the spontaneous-report data and, with the exception of rare reports of an unpleasant taste, the most commonly reported events have been the same as those seen in clinical studies. These data support grepafloxacin as a well-tolerated fluoroquinolone suitable for the treatment of community-acquired respiratory tract infections.

Grepafloxacin: microbiological properties

Grepafloxacin is a new broad-spectrum fluoroquinolone characterized by having a methyl-substituted piperazine at the 7 position. It is a water-soluble racemate with both stereoisomers having the same activity. Its mode of action involves inhibition of topoisomerases II and IV. Grepafloxacin is not recognized by the NorA efflux mechanism in Staphylococcus aureus and, thus, some strains of Staphylococcus aureus that are resistant to other fluoroquinolones remain susceptible to grepafloxacin. Grepafloxacin has potent in vitro activity against streptococci and staphylococci, respiratory Gram-negative pathogens, atypical respiratory pathogens and sexually transmitted disease pathogens. It combines the positive properties of the beta-lactams against conventional Gram-positive and Gram-negative respiratory pathogens with the activity of the macrolides against the atypical pathogens. Unlike macrolides, it is bactericidal at concentrations close to the MIC. Its in vitro activity has been reflected in animal models of respiratory tract infections. Concentrations above MICs are maintained throughout nearly all of the 24-h dosing interval. Grepafloxacin provides important improvements over older quinolones and over other classes of antibiotics.

Grepafloxacin: pharmacokinetics and tissue penetration

Pharmacokinetic and tissue penetration studies of grepafloxacin, a new broad-spectrum fluoroquinolone, show that it has useful properties for the treatment of respiratory tract infections. Grepafloxacin has a volume of distribution that is larger than those of many of the other fluoroquinolones and is concentrated in alveolar macrophages, bronchial mucosa and epithelial lining fluid to a greater extent than are certain other fluoroquinolones. Grepafloxacin concentrations achieved in plasma after a 400-mg oral dose are well in excess of those required to inhibit the respiratory pathogens Staphylococcus aureus, Haemophilus influenzae and Moraxella catarrhalis. Streptococcus pneumoniae is also covered for most of the dosing interval, but at normal dose levels grepafloxacin might not inhibit Enterococcus faecalis. The maximum plasma concentrations and area under the concentration---time curve achieved with grepafloxacin suggest that it will be effective for the treatment of community-acquired pneumonia and acute exacerbations of chronic bronchitis. The pharmacokinetics of fluoroquinolones are among their most useful properties. The aim of this paper is to demonstrate whether the differences between grepafloxacin and the other fluoroquinolones are of therapeutic significance.

Effect of age and gender on the pharmacokinetics of grepafloxacin

The effects of age and gender on the pharmacokinetics of the oral fluoroquinolone grepafloxacin were examined in 48 healthy middle-aged and elderly individuals, of whom half were male and half were female. Participants were stratified into 4 groups (each with n = 12), aged 40 to 49 years, 50 to 59 years, 60 to 69 years, and > 70 years. All received oral grepafloxacin 600 mg once daily for 7 days, and pharmacokinetic parameters were measured on days 1 and 7. Mean plasma grepafloxacin concentrations were consistently higher in females than in males. Peak concentrations, area under the concentration-time curve, apparent volume of distribution and apparent total clearance (but not renal clearance) differed significantly in females and males. There were no significant gender differences in the elimination half-life values. Further analysis of the data suggests that the gender-related pharmacokinetic differences were primarily due to differences in bodyweight, in particular to differences in lean body mass. The only parameters that changed significantly with age were renal clearance and the proportion of the dose excreted unchanged in the urine, but no clear trend was observed, and there was no correlation with creatinine clearance. We conclude that age and gender have no clinically significant effect on the pharmacokinetics of grepafloxacin. Dose adjustment on the basis of these factors does not therefore seem necessary.

Efficacy and safety of a 10-day course of 400 or 600 milligrams of grepafloxacin once daily for treatment of acute bacterial exacerbations of chronic bronchitis: comparison with a 10-day course of 500 milligrams of ciprofloxacin twice daily

A randomized, prospective, double-blind, double-dummy, multicenter study investigated the efficacy and safety of 10 days of oral therapy with grepafloxacin at 400 mg once daily, grepafloxacin at 600 mg once daily, or ciprofloxacin at 500 mg twice daily in 624 patients with acute bacterial exacerbations of chronic bronchitis. At the end of treatment, clinical success (cure or improvement) was achieved for 93% (140 of 151), 88% (137 of 156), and 91% (145 of 160) of patients in the groups receiving grepafloxacin at 400 mg, grepafloxacin at 600 mg, and ciprofloxacin, respectively (clinically evaluable population). At follow-up (14 to 28 days posttreatment), the clinical success rates were 87% (124 of 143), 81% (122 of 151), and 80% (123 of 154) in the groups receiving grepafloxacin at 400 mg and 600 mg and ciprofloxacin, respectively. A total of 379 pathogens were isolated from 290 patients, with the most common isolates being Moraxella catarrhalis (21%), Staphylococcus aureus (20%), Haemophilus influenzae (18%), and Streptococcus pneumoniae (7%). For the evaluable population, successful bacteriologic response was obtained at the end of treatment for 96% (92 of 96), 98% (87 of 89), and 92% (82 of 90) of patients receiving grepafloxacin at 400 mg, grepafloxacin at 600 mg, and ciprofloxacin, respectively, and was maintained in 86% (82 of 95), 88% (78 of 89), and 82% (69 of 84) of patients, respectively, at follow-up. All pretreatment S. pneumoniae isolates were susceptible to grepafloxacin, but two strains were resistant to ciprofloxacin. All treatments were well tolerated, with the most frequently reported drug-related adverse events being nausea, taste perversion, and headache. All drug-related adverse events in the grepafloxacin groups were mild or moderate in severity. This study demonstrates that 10-day courses of grepafloxacin given at 400 or 600 mg once daily were as effective, clinically and bacteriologically, as ciprofloxacin given at 500 mg twice daily for the treatment of acute bacterial exacerbations of chronic bronchitis.