In-vitro activity of OPC-17116 against more than 6000 consecutive clinical isolates: a multicentre international study

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.

Contemporary re-evaluation of the activity and spectrum of grepafloxacin tested against isolates in the United States

Grepafloxacin potency and spectrum of activity were re-evaluated against contemporary pathogens collected from clinical infections in 2001-2002. A total of 995 isolates were tested for grepafloxacin by the reference agar dilution method and these results were compared to those of 25 other antimicrobial agents. Grepafloxacin activity remained comparable to that of ciprofloxacin, levofloxacin and gatifloxacin against Escherichia coli, Klebsiella pneumoniae and Enterobacter cloacae (MIC(90), 0.03-2 microg/ml; 0.0-7.7% resistance rates). For Pseudomonas aeruginosa, grepafloxacin was active against ciprofloxacin-susceptible (MIC(90), 2 microg/ml), but not against ciprofloxacin-resistant (MIC(90), >8 microg/ml) isolates. Against methicillin-susceptible Staphylococcus aureus, grepafloxacin susceptibility rate was 91.4%, equal to that of levofloxacin. None of the fluoroquinolones showed reasonable activity against methicillin-resistant staphylococci. Gatifloxacin and grepafloxacin had the same MIC(90) against beta-hemolytic streptococci (0.25 microg/ml) and penicillin-susceptible Streptococcus pneumoniae (0.25 microg/ml). Grepafloxacin and other fluoroquinolone activities were not influenced by penicillin resistance in S. pneumoniae. Grepafloxacin was very active against Haemophilus influenzae (MIC(90), 0.03 microg/ml), Moraxella catarrhalis (MIC(90), 0.03 microg/ml) and Legionella spp. (MIC(90), 0.5 microg/ml). These results on recently isolated organisms indicate that grepafloxacin has a sustained potency and spectrum against most clinically important and indicated pathogens.

A critical review of the fluoroquinolones: focus on respiratory infections

The new fluoroquinolones (clinafloxacin, gatifloxacin, gemifloxacin, grepafloxacin, levofloxacin, moxifloxacin, sitafloxacin, sparfloxacin and trovafloxacin) offer excellent activity against Gram-negative bacilli and improved Gram-positive activity (e.g. against Streptococcus pneumoniae and Staphylococcus aureus) over ciprofloxacin. Ciprofloxacin still maintains the best in vitro activity against Pseudomonas aeruginosa. Clinafloxacin, gatifloxacin, moxifloxacin, sitafloxacin, sparfloxacin and trovafloxacin display improved activity against anaerobes (e.g. Bacteroides fragilis) versus ciprofloxacin. All of the new fluoroquinolones display excellent bioavailability and have longer serum half-lives than ciprofloxacin allowing for once daily dose administration. Clinical trials comparing the new fluoroquinolones to each other or to standard therapy have demonstrated good efficacy in a variety of community-acquired respiratory infections (e.g. pneumonia, acute exacerbations of chronic bronchitis and acute sinusitis). Limited data suggest that the new fluoroquinolones as a class may lead to better outcomes in community-acquired pneumonia and acute exacerbations of chronic bronchitis versus comparators. Several of these agents have either been withdrawn from the market, had their use severely restricted because of adverse effects (clinafloxacin because of phototoxicity and hypoglycaemia; grepafloxacin because of prolongation of the QTc and resultant torsades de pointes; sparfloxacin because of phototoxicity; and trovafloxacin because of hepatotoxicity), or were discontinued during developmental phases. The remaining fluoroquinolones such as gatifloxacin, gemifloxacin, levofloxacin and moxifloxacin have adverse effect profiles similar to ciprofloxacin. Extensive post-marketing safety surveillance data (as are available with ciprofloxacin and levofloxacin) are required for all new fluoroquinolones before safety can be definitively established. Drug interactions are limited; however, all fluoroquinolones interact with metal ion containing drugs (eg. antacids). The new fluoroquinolones (gatifloxacin, gemifloxacin, levofloxacin and moxifloxacin) offer several advantages over ciprofloxacin and are emerging as important therapeutic agents in the treatment of community-acquired respiratory infections. Their broad spectrum of activity which includes respiratory pathogens such as penicillin and macrolide resistant S. pneumoniae, favourable pharmacokinetic parameters, good bacteriological and clinical efficacy will lead to growing use of these agents in the treatment of community-acquired pneumonia, acute exacerbations of chronic bronchitis and acute sinusitis. These agents may result in cost savings especially in situations where, because of their potent broad-spectrum activity and excellent bioavailability, they may be used orally in place of intravenous antibacterials. Prudent use of the new fluoroquinolones will be required to minimise the development of resistance to these agents.

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.

Gemifloxacin and ciprofloxacin pharmacodynamics in an in-vitro dynamic model: prediction of the equivalent AUC/MIC breakpoints and doses

To compare the antimicrobial effects (AMEs) of gemifloxacin (GEM) and ciprofloxacin (CIP) on Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa, a series of pharmacokinetic profiles of GEM (a single dose with the half-life (T(1/2)) of 7.4 h and CIP (two 12 h doses with T(1/2) of 4 h) were simulated in vitro over eight-fold ranges of the AUC/MIC ratio. Species- and strain-independent linear relationships observed between the intensity of AME (I(E)) and log AUC/MIC were not superimposed for GEM and CIP (r(2)=0.99 and 0.98, respectively). The predicted ratio for GEM that might be equivalent to a clinically established breakpoint value of AUC/MIC=125 (mg h/l)/(mg/l) for CIP was estimated at 110 (mg h/l)/(mg/l). It was calculated, that a daily dose of CIP that might provide the same AME as a clinical dose of GEM (320 mg) on a hypothetical strain of S. aureus with MICs=MIC(50)s would be as high as 2 x 3200 mg.

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.

Activity of newer fluoroquinolones in vitro against gram-positive bacteria

Several newer fluoroquinolones, which have been recently introduced or are under investigation, display substantially greater potency against gram-positive organisms than the older generation agents of this class. Nevertheless, for problem organisms including methicillin-resistant strains of Staphylococcus aureus and many Enterococcus faecium, concentrations of newer antimicrobials required to inhibit 90% of organisms in the collections studied remain above those that are projected to be achievable with clinical use. Nevertheless, enhanced potency of several newer quinolones may result in a favourable pharmacodynamic profile leading to improved outcomes against gram-positive infections and possibly to the delayed or diminished emergence of resistance to these agents.

Randomized, double-blind study of short-course (5 day) grepafloxacin versus 10 day clarithromycin in patients with acute bacterial exacerbations of chronic bronchitis

The efficacy and safety of grepafloxacin were compared with clarithromycin in a randomized, double-blind, multicentre clinical trial of 805 patients with acute bacterial exacerbations of chronic bronchitis (ABECB). Patients were randomized to receive grepafloxacin 400 mg od for either 5 (n = 273) or 10 days (n = 268) or clarithromycin 250 mg bd for 10 days (n = 261). Patients were assessed pre-treatment, 3-5 days during treatment, 1-3 days post-treatment and at follow-up (21-28 days post-treatment). The clinical success rates for the evaluable patients were 91% in the 5 day grepafloxacin group, 95% in the 10 day grepafloxacin group and 86% in the clarithromycin group. At follow-up, respective rates were 72%, 81% and 73%. A total of 513 pathogens were isolated from the pre-treatment sputum specimens of 400 (49%) patients. The primary pathogens were Haemophilus influenzae (36% of isolates), Haemophilus parainfluenzae (27%), Moraxella catarrhalis (12%), Streptococcus pneumoniae (11%) and Staphylococcus aureus (3%). Pathogens were eradicated or presumed eradicated at post-treatment in 85%, 91% and 58% of evaluable patients treated with grepafloxacin for 5 days, grepafloxacin 10 days and clarithromycin 10 days, respectively. The eradication rates in both grepafloxacin groups were significantly greater than the clarithromycin group (P<0.001). All treatments were well tolerated and incidence of drug-related adverse events in each group was comparable. This study demonstrates that both a 5 and a 10 day regimen of grepafloxacin 400 mg od are as clinically and bacteriologically effective as in the treatment of ABECB clarithromycin 250 mg bd. for 10 days.

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.

Antipneumococcal activity of grepafloxacin compared to that of other agents by time-kill methodology

Time-kill studies compared the activities of grepafloxacin with those of ciprofloxacin, levofloxacin, sparfloxacin, amoxicillin-clavulanate, and clarithromycin against 12 pneumococcal strains. Grepafloxacin was bactericidal after 24 h against all strains at a concentration of < or = 0.5 microg/ml, while sparfloxacin, levofloxacin, and ciprofloxacin were bactericidal at concentrations of < or = 1.0, < or = 2.0, and < or = 8.0 microg/ml, respectively. Amoxicillin-clavulanate and clarithromycin were bactericidal at 2x the MIC after 24 h against 12 of 12 strains and against all 8 macrolide-susceptible strains, respectively.

Structure of grepafloxacin relative to activity and safety profile

A comparison of the structure of ciprofloxacin and grepafloxacin shows that the two compounds are similar, with two exceptions: grepafloxacin has a methyl group at the 5 position and a methyl group attached to the 7-piperazinyl substituent. At the 1 position, both compounds have a cyclopropyl group, which is important for potency, but limits anaerobic activity. The methylpiperazine at position 7 in grepafloxacin is associated with its enhanced Gram-positive activity and long half-life. The methyl group at R5 is also thought to enhance Gram-positive activity. Ciprofloxacin's piperazine group at the 7 position is associated with good Gram-negative activity. Grepafloxacin's Gram-negative activity is comparable to that of ciprofloxacin's against Haemophilus influenzae, Moraxella catarrhalis and enteric Gram-negative bacilli. Studies of resistance development to fluoroquinolones suggest that grepafloxacin is associated with a reduced selection of resistance in Staphylococcus aureus, which is possibly related to the inhibition or avoidance of efflux transport by NorA.

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.

Ciprofloxacin. An updated review of its pharmacology, therapeutic efficacy and tolerability

Ciprofloxacin is a broad spectrum fluoroquinolone antibacterial agent. Since its introduction in the 1980s, most Gram-negative bacteria have remained highly susceptible to this agent in vitro; Gram-positive bacteria are generally susceptible or moderately susceptible. Ciprofloxacin attains therapeutic concentrations in most tissues and body fluids. The results of clinical trials with ciprofloxacin have confirmed its clinical efficacy and low potential for adverse effects. Ciprofloxacin is effective in the treatment of a wide variety of infections, particularly those caused by Gram-negative pathogens. These include complicated urinary tract infections, sexually transmitted diseases (gonorrhoea and chancroid), skin and bone infections, gastrointestinal infections caused by multiresistant organisms, lower respiratory tract infections (including those in patients with cystic fibrosis), febrile neutropenia (combined with an agent which possesses good activity against Gram-positive bacteria), intra-abdominal infections (combined with an antianaerobic agent) and malignant external otitis. Ciprofloxacin should not be considered a first-line empirical therapy for respiratory tract infections if penicillin-susceptible Streptococcus pneumoniae is the primary pathogen; however, it is an appropriate treatment option in patients with mixed infections (where S. pneumoniae may or may not be present) or in patients with predisposing factors for Gram-negative infections. Clinically important drug interactions involving ciprofloxacin are well documented and avoidable with conscientious prescribing. Recommended dosage adjustments in patients with impaired renal function vary between countries; major adjustments are not required until the estimated creatinine clearance is < 30 ml/min/1.73m2 (or when the serum creatinine level is > or = 2 mg/dl). Ciprofloxacin is one of the few broad spectrum antibacterials available in both intravenous and oral formulations. In this respect, it offers the potential for cost savings with sequential intravenous and oral therapy in appropriately selected patients and may allow early discharge from hospital in some instances. In conclusion, ciprofloxacin has retained its excellent activity against most Gram-negative bacteria, and fulfilled its potential as an important antibacterial drug in the treatment of a wide range of infections. Rational prescribing will help to ensure the continued clinical usefulness of this valuable antimicrobial drug.

In vitro activity of fluoroquinolones against gram-positive bacteria

This paper reviews the in vitro activities of several newer fluoroquinolone antimicrobials that exhibit enhanced potency against Gram-positive bacteria. Several of these agents demonstrate 10-fold greater activity than older members of this class against Staphylococcus aureus and inhibit [minimum inhibitory concentration (MIC90) values < or = 2 mg/L] many isolates resistant to ciprofloxacin or ofloxacin. Markedly enhanced activity is also noted against Streptococcus pneumoniae, 90% of isolates being inhibited at concentrations 10- to 100-fold lower than those of the older agents. Enterococci also exhibit greater susceptibility to several of the newer fluoroquinolones, although relative cross-resistance with the earlier drugs is noted. As determined by dilution techniques, the new fluoroquinolones generally demonstrate bactericidal activity at concentrations at or near their MIC values. The activities of the new compounds described here are decreased at low pH, but are not affected by the addition of up to 50% human serum to the test medium. Resistance is rarely detected (frequency < 10(-9)) when high density bacterial suspensions are plated in the presence of 4 times the MIC of these compounds. However, colonies displaying relative resistance to the new agents can be selected by serial passage in incremental antimicrobial concentrations.