Multicenter in vitro comparative study of fluoroquinolones against 25,129 gram-positive and gram-negative clinical isolates

Potential new fluoroquinolone treatments for suspected bacterial keratitis

Topical fluoroquinolones (FQs) are an established treatment for suspected microbial keratitis. An increased FQ resistance in some classes of bacterial pathogens is a concern. Some recently developed FQs have an extended spectrum of activity, making them a suitable alternative for topical ophthalmic use. For example, the new generation FQs, avarofloxacin, delafloxacin, finafloxacin, lascufloxacin, nadifloxacin, levonadifloxacin, nemonoxacin and zabofloxacin have good activity against the common ophthalmic pathogens such as Staphylococcus aureus, Pseudomonas aeruginosa, Streptococcus pneumoniae and several of the Enterobacteriaceae. However, because there are no published ophthalmic break-point concentrations, the susceptibility of an isolated micro-organism to a topical FQ is extrapolated from systemic break-point data and wild type susceptibility. The purpose of this review is to compare the pharmacokinetics and pharmacodynamics of the FQs licensed for topical ophthalmic use with the same parameters for new generation FQs. We performed a literature review of the FQs approved for topical treatment and the new generation FQs licensed to treat systemic infections. We then compared the minimum inhibitory concentrations (MIC) of bacterial isolates and the published concentrations that FQs achieved in the cornea and aqueous. We also considered the potential suitability of new generation FQs for topical use based on their medicinal properties. Notably, we found significant variation in the reported corneal and aqueous FQ concentrations so that reliance on the reported mean concentration may not be appropriate, and the first quartile concentration may be more clinically relevant. The provision of the MIC for the microorganism together with the achieved lower (first) quartile concentration of a FQ in the cornea could inform management decisions such as whether to continue with the prescribed antimicrobial, increase the frequency of application, use a combination of antimicrobials or change treatment.

Preclinical assessment of scleral lens as a reservoir-based ocular therapeutic system

PURPOSE

Bacterial keratitis is a sight threatening infection of the cornea which remains one of the most important potential complications of contact lens use. If the corneal ulcer is small, peripheral with no impending perforation present, intensive monotherapy with fluoroquinolones could be used. Therefore, a study was conducted with the objective to provide pharmacological data of the intra-ocular diffusion after administration of Ofloxacin using a scleral lens reservoir, as well as an evaluation of surface tolerability in rabbits.

MATERIALS AND METHODS

Samples of corneas, aqueous humor and vitreous were collected to measure the drug levels of Ofloxacin using High Performance Liquid Chromatography. The corneas were examined by electron microscopy scanning and the eyeballs by light polarizing microscopy in order to evaluate surface tolerability.

RESULTS

Ofloxacin levels found in the aqueous humor and cornea were higher than those previously reported. The mean Ofloxacin corneal levels exceeded the MIC (Minimum Inhibitory Concentration) for which 90% of isolates are indicated for all bacteria implicated in keratitis.

CONCLUSION

To our knowledge, this is the first preclinical study assessing local tolerance and intra-ocular diffusion of Ofloxacin after administration using a scleral lens reservoir.

Ciprofloxacin as Treatment for Conjunctivitis

The authors studied the bactericidal action and therapeutic effectiveness of ciprofloxacin in treating external ocular infections (bacterial conjunctivitis and bacterial blepharoconjunctivitis). 108 ambulatory patients with clinical signs of conjunctivitis and blepharoconjunctivitis were enrolled in the study. All subjects underwent a conjunctival swab before starting therapy and at 10 days, to identify the causative bacteria and their susceptibility to ciprofloxacin, following routine microbiological methods. The reported therapeutic success rate (95%) and bacteriological analysis confirmed the effectiveness of ciprofloxacin in subjects with bacterial conjunctivitis and bacterial blepharoconjunctivitis. In vitro tests conducted 10 days after treatment confirmed the in vivo therapeutic effectiveness, even for those infections characterized by a difficult etiological identification which interferes with specific antibiotic therapy.

Fluoroquinolones in paediatrics: a risk for the patient or for the community?

Fluoroquinolones are an important group of antibiotics widely used in adult patients because of their excellent tissue penetration and their bactericidal activity. They are not authorised for paediatric use (except the limited indication of pseudomonas infections in cystic fibrosis), however, because of the potential for joint toxicity reported from experiments with young animals. Despite the absence of official approval, fluoroquinolones are widely used in paediatrics as second-line antibiotics when all other treatments have failed. Most of the information available about paediatric use concerns ciprofloxacin, which is used in children much more often than the other members of this class. The published paediatric series have shown that frequency of articular side-effects varies according to age: all the surveys have reported frequencies of around 0.1% in adults and 2-3% in children. Outside of cystic fibrosis and severe infections in which no other treatment is possible, the only paediatric situations where fluoroquinolones are superior to standard treatments for children, in speed of recovery and comfort as well as in efficacy, are typhoid fever, severe shigella dysenteries, and enterobacteria meningitis. Should the use of new fluoroquinolones active against pneumococci be authorised for upper respiratory infections (including recurrent otitis) in children, the potential emergence and dissemination of pneumococci strains in which multidrug resistance includes fluoroquinolones would create a real risk in the community. It is, therefore, important to continue the policy of second-line use in children, only after failure of an earlier treatment, and when other antibiotics approved for paediatric use cannot be used.

Emerging antibiotic resistance in urinary tract pathogens

In vitro antimicrobial resistance is an evolving and growing problem in UTI. Much of the increase is occurring in acute uncomplicated cystitis, an infection that has traditionally been simple to treat. The current trend of rising TMP-SMX and beta-lactam resistance rates is worrisome. Of more concern, however, are the emerging issues of fluoroquinolone resistance and MDR among community-acquired urinary isolates. Judicious use of antibiotics and development of novel nonantimicrobial-based methods of prevention of UTI are important strategies to help slow the progression of resistance. In the meantime, ongoing surveillance of resistance trends and enhanced understanding of the determinants of resistance are crucial for optimal management of UTIs.

Penetration of topically administered ofloxacin and trimethoprim into aqueous humor

Ocular penetration of two topical antibiotics used to treat bacterial conjunctivitis was assessed in adult volunteers scheduled for cataract surgery. In this randomized, parallel-group study, patients instilled trimethoprim sulfate 0.1%/polymyxin B (n = 23) or ofloxacin 0.3% (n = 25) QID for 3 days, plus 4 instillations in the hour before surgery. Analysis of aqueous humor samples obtained during surgery showed a 2.4-fold greater concentration of ofloxacin over trimethoprim (1.135 micro g/ml vs 0.470 micro g/ml; P <.0001). The greater concentration of ofloxacin in ocular tissue coupled with its superior antibacterial activity profile supports its use as an alternative to trimethoprim/polymyxin B for treatment of bacterial conjunctivitis.

Susceptibility to fluoroquinolones among commonly isolated Gram-negative bacilli in 2000: TRUST and TSN data for the United States. Tracking Resistance in the United States Today. The Surveillance Network

From January to May 2000, as part of the Tracking Resistance in the United States Today (TRUST) surveillance initiative, clinical isolates of Enterobacteriaceae (n=2519) and non-fermentative Gram-negatives (n=580) were prospectively collected from 26 hospital laboratories across the United States. Isolates were tested for susceptibility to three fluoroquinolones (ciprofloxacin, levofloxacin, gatifloxacin) and seven other agents. In addition, data for the same period were collected from The Surveillance Network (TSN) Database-USA, an electronic surveillance network that receives data from more than 200 laboratories in the US. Both surveillance methods produced similar results. Against isolates of Enterobacteriaceae, imipenem was the most active agent, followed by the fluoroquinolones; > or = 86.7% of isolates of all species of Enterobacteriaceae except Providencia spp. were susceptible to fluoroquinolones by TRUST and TSN surveillance. TRUST identified differences in susceptibility to the three fluoroquinolones of > or = 2% for Citrobacter spp., Enterobacter cloacae, Proteus mirabilis and Serratia marcescens. Isolates of P. mirabilis were considerably more susceptible to levofloxacin (94.0%) than to ciprofloxacin (87.7%) and gatifloxacin (87.7%). Other results from TRUST included Pseudomonas aeruginosa being slightly more susceptible to ciprofloxacin (73.5%) and levofloxacin (73.0%) than gatifloxacin (71.0%). Imipenem was the only compound with significant activity (95.1% susceptible, TRUST; 87.4% susceptible, TSN) against Acinetobacter baumannii, but it was inactive against Stenotrophomonas maltophilia. S. maltophilia isolates were more susceptible to levofloxacin and gatifloxacin (77.7-79.8%) than ciprofloxacin (29.7-33.0%). Against 513 urinary isolates of Escherichia coli in TRUST, levofloxacin, gatifloxacin and ciprofloxacin were equipotent. Age and gender had no clear effect on the activity of levofloxacin, ciprofloxacin or gatifloxacin. Similar results for all three fluoroquinolones were seen in outpatients and inpatients. TRUST and TSN data indicated that resistance rates had not changed appreciably for any compound studied since a similar study conducted in 1999. TRUST centralized in vitro and electronic (TSN) surveillance methods provided an effective strategy for monitoring trends in resistance.

Fluoroquinolones: place in ocular therapy

The fluoroquinolones have become widely used antibacterial agents in the treatment of ocular infections, with topical, intravitreal and systemic routes of administration being used. In general, fluoroquinolones (such as ciprofloxacin, ofloxacin, lomefloxacin and norfloxacin) have good activity against gram-negative and gram-positive bacteria. Therapeutic concentrations are achieved in the cornea after topical administration so that the fluoroqinolones have largely replaced combination therapy for the treatment of bacterial keratitis. However, a second line agent is needed when resistance is likely, such as in disease caused by streptococcal species. Reversal of resistance to quinolones may not occur with withdrawal of the antibacterial. This stresses the importance of prudent prescribing to reduce the occurrence of resistance to quinolones. When used in therapeutic topical dosages, corneal toxicity does not occur. Similarly, retinal toxicity is not seen when fluoroquinolones are used at therapeutic dosages, systemically or topically. Corneal precipitation occurs, particularly with ciprofloxacin and to a lesser extent norfloxacin, but does not appear to interfere with healing. In the treatment of endophthalmitis there is reasonable penetration of systemic fluoroquinolones into the vitreous but sufficiently high concentrations to reach the minimum inhibitory concentration for 90% of isolates (MIC90) of all important micro-organisms may not be guaranteed. Systemic administration may be useful for prophylaxis after ocular trauma.

Fluoroquinolones in paediatrics

The fluoroquinolones are an important group of antibiotics, which are widely used in adult patients because of their high penetration in tissues and bactericidal activity. However, they are not licensed for paediatric use (except the limited indication of Pseudomonas infection in cystic fibrosis) because of their potential to cause joint toxicity (observed in experiments using juvenile animal models). In recent years, there has been a change in the susceptibility of pathogens to widely used antibiotics; however, many of these pathogens remain sensitive to the fluoroquinolones (agents which can often be administered orally to treat severe infections). Fluoroquinolones have a number of potential indications in children: cystic fibrosis, intestinal infections due to resistant strains of Salmonella spp. and Shigella spp., severe infections due to Enterobacteriaceae (including the neonatal period), complicated urinary tract infections, the immunocompromised host, and some mycobacterial infections. The third generation fluoroquinolones have improved activity against Gram-positive bacteria and could be useful in respiratory tract, and ear, nose and throat infections in adult patients. Their potential role in routine use for paediatric patients will remain limited because of potential joint complications and the availability of other treatment options. However, available clinical data does indicate that the incidence of arthrotoxicity in children treated with ciprofloxacin appears to be the same as that in adult patients. The use of other fluoroquinolones is too rare to obtain meaningful information on their toxicity in children. For future fluoroquinolones, pneumococcal meningitis will probably be a potential indication. Despite their important activity, fluoroquinolones remain a second-line treatment in children, for use following the failure of a well established antibiotic treatment, to avoid potential adverse effects and the emergence of resistant strains.

In vitro susceptibilities of bacterial ocular isolates to fluoroquinolones

PURPOSE

To evaluate and compare the in vitro antimicrobial activity of levofloxacin versus ciprofloxacin and ofloxacin against ocular isolates from patients with bacterial conjunctivitis.

METHODS

The in vitro antimicrobial susceptibilities of ocular isolates to levofloxacin, ofloxacin, and ciprofloxacin were determined using both the agar disk diffusion and broth dilution methods.

RESULTS

Disk diffusion susceptibility testing disclosed that 99% (100 of 101 isolates) of gram-negative isolates and 98% (127 of 129 isolates) of gram-positive isolates were susceptible to levofloxacin; 96% (97 of 101 isolates) of gram-negative isolates and 78% (100 of 129 isolates) of gram-positive isolates were susceptible to ofloxacin; and 94% (95 of 101 isolates) of gram-negative isolates and 61% (79 of 129 isolates) of gram-positive isolates were susceptible to ciprofloxacin. Broth dilution testing disclosed that 99% (72 of 73 isolates) of gram-negative isolates and 98% (111 of 113 isolates) of gram-positive isolates were susceptible to levofloxacin; 96% (70 of 73 isolates) of gram-negative isolates and 92% (104 of 113 isolates) of gram-positive isolates were susceptible to ofloxacin; and 95% (69 of 73 isolates) of gram-negative isolates and 82% (93 of 113 isolates) of gram-positive isolates were susceptible to ciprofloxacin.

CONCLUSIONS

In this study, levofloxacin demonstrated superior in vitro activity against human bacterial conjunctival isolates compared with either ofloxacin or ciprofloxacin (levofloxacin > ofloxacin > ciprofloxacin).

Resistance pattern of 2816 isolates isolated from 17631 blood cultures and etiology of bacteremia and fungemia in a single cancer institution

The resistance pattern of 2816 isolates from 17631 blood cultures and the etiology of isolates causing bacteremia and fungemia among 14591 admissions were investigated in an 80-bed single cancer institute during seven years (1990-1996) under the same empiric therapeutic antibiotic policy but with different prophylactic strategies. No change was found in the proportion of Gram-positive versus Gram-negative bacteria isolated from bacteremias (70% vs. 30%) during the past seven years. Furthermore, the proportion of coagulase-negative staphylococci and enterococci was about the same before and after the introduction of ofloxacin in prophylaxis. However, the proportion of Pseudomonas aeruginosa and Stenotrophomonas maltophilia causing bacteremia increased. There was no increase in Candida krusei and Candida glabrata after the introduction of fluconazole into our prophylactic regimen in 1992. Penicillin-resistance in viridans streptococci increased after penicillin was introduced into prophylaxis in acute leukemia in 1993. Until 1995 no quinolone-resistant Enterobacteriaceae were observed. Susceptibility to quinolones did not significantly change within the past seven years in Enterobacteriaceae after their introduction to prophylaxis in 1991, but Pseudomonas aeruginosa decreased from 90 to 58.2%. Glycopeptide resistance in enterococci and staphylococci was minimal in the observed period (0.9-4.3%).

Evaluation of current activities of fluoroquinolones against gram-negative bacilli using centralized in vitro testing and electronic surveillance

Given the propensity for Enterobacteriaceae and clinically significant nonfermentative gram-negative bacilli to acquire antimicrobial resistance, consistent surveillance of the activities of agents commonly prescribed to treat infections arising from these organisms is imperative. This study determined the activities of two fluoroquinolones, levofloxacin and ciprofloxacin, and seven comparative agents against recent clinical isolates of Enterobacteriaceae, Pseudomonas aeruginosa, Acinetobacter baumannii, and Stenotrophomonas maltophilia using two surveillance strategies: 1) centralized in vitro susceptibility testing of isolates collected from 27 hospital laboratories across the United States and 2) analysis of data from The Surveillance Network Database-USA, an electronic surveillance network comprising more than 200 laboratories nationwide. Regardless of the surveillance method, Enterobacteriaceae, P. aeruginosa, and A. baumannii demonstrated similar rates of susceptibility to levofloxacin and ciprofloxacin. Susceptibilities to the fluoroquinolones approached or exceeded 90% for all Enterobacteriaceae except Providencia spp. (</=65%). Approximately 70% of P. aeruginosa and 50% of A. baumanii isolates were susceptible to both fluoroquinolones. Among S. maltophilia isolates, 50% more isolates were susceptible to levofloxacin than to ciprofloxacin. Overall, the rate of ceftazidime nonsusceptibility among Enterobacteriaceae was 8.7%, with fluoroquinolone resistance rates notably higher among ceftazidime-nonsusceptible isolates than ceftazidime-susceptible ones. Multidrug-resistant isolates were present among all species tested but were most prevalent for Klebsiella pneumoniae and Enterobacter cloacae. No gram-negative isolates resistant only to a fluoroquinolone were encountered, regardless of species. Thus, while levofloxacin and ciprofloxacin have maintained potent activity against Enterobacteriaceae, the potential for fluoroquinolone resistance, the apparent association between fluoroquinolone and cephalosporin resistance, and the presence of multidrug resistance in every species examined emphasize the need to maintain active surveillance of resistance patterns among gram-negative bacilli.

Ciprofloxacin disposition in elderly patients with LRTI being treated with sequential therapy (200 mg intravenously twice daily followed by 500 mg per os twice daily): comparative pharmacokinetics and the role of therapeutic drug monitoring

Ciprofloxacin is a fluoroquinolone antibiotic effective in the treatment of lower respiratory tract infections (LRTI). The aim of this study was to assess the pharmacokinetic appropriateness of a standard switch i.v./os regimen of ciprofloxacin (200 mg i.v. bid for 3 to 5 days followed by 500 mg os bid for 7 to 10 days) frequently used in routine clinical practice in the treatment of elderly patients with mild to moderate LRTI. The pharmacokinetic study was performed on a cohort of 17 elderly inpatients. Blood samples were collected in steady state conditions at appropriate intervals. Ciprofloxacin serum concentrations were analyzed using an HPLC method and pharmacokinetic parameters were estimated using the WinNonlin software package. The pharmacokinetic data were at least partially different from those obtained by other authors in elderly patients (lower Cmax after i.v. administration and higher CL both after i.v. and oral administration). Cmax after a 1-hour 200-mg infusion were similar to those observed during the 500 mg bid peroral regimen (2.1 +/- 0.9 mg/L vs 2.6 +/- 1.0 mg/L; p = 0.054). The absolute oral bioavailability (84.1%) allowed a total body exposure 2.1-fold greater after 500 mg bid oral administration than after 200 mg bid i.v. administration (AUC(0-tau) 11.4 +/- 4.3 mg/L x h vs 5.5 +/- 1.8 mg/L x h). The results show that in malabsorption-free elderly patients a regimen of 500 mg os bid may be considered a valid therapeutic approach from the beginning of therapy for mild to moderate LRTI caused by sensitive microorganisms (MIC < 0.1 mg/L). In fact, because the peak serum level to MIC ratio (Cmax/MIC) and the area under the inhibitory serum concentration-time curve (AUIC24 = AUC24h/MIC) are actually considered major pharmacodynamic determinants for the outcome of treatment with fluoroquinolones, this regimen could guarantee both a better pharmacokinetic exposure than the 200 mg i.v. bid regimen and a cost-effective treatment of LRTI. However, because of the great pharmacokinetic interindividual variability observed a normalized dosage per kg (3 mg/kg/12h i.v. and 8 mg/kg/12h os) should be considered, especially for body weight >90 kg and, whenever possible, TDM of AUC(0-tau) or at least of Cmax should be performed to individualize therapy in this subpopulation.

Expanded activity and utility of the new fluoroquinolones: a review

In general, the fluoroquinolones developed over the past few years have greater potency, a broader spectrum of antimicrobial activity, greater in vitro efficacy against resistant organisms, and a better safety profile than other antimicrobial agents, including the older quinolones. The present review focuses on 4 new quinolones that are commercially available (levofloxacin, trovafloxacin, grepafloxacin, and sparfloxacin) and 3 that are currently undergoing clinical trials (gatifloxacin, moxifloxacin, and clinafloxacin). Examination of the minimum inhibitory concentrations of these drugs against gram-positive, gram-negative, anaerobic, and atypical organisms demonstrates their increased potency in vitro. The available clinical evidence, although sparse, suggests the potential enhanced efficacy of these drugs in the treatment of various community-acquired and nosocomial infections (eg, respiratory, urinary tract, and skin infections and sexually transmitted diseases). Compared with ciprofloxacin, their pharmacokinetic profiles demonstrate equivalent or greater bioavailability, higher plasma concentrations, and increased tissue penetration, as reflected in greater volume of distribution. Adverse events seen with most quinolones are mild. Serious adverse effects that may occur are phototoxicity (particularly with sparfloxacin) and prolongation of the QTc interval (seen with sparfloxacin and grepafloxacin). Drug interactions are possible between multivalent cation-containing compounds and all quinolones and between theophylline and both ciprofloxacin and grepafloxacin. Drugs that prolong the QTc interval should not be coadministered with sparfloxacin and grepafloxacin. Step-down therapy, a therapeutic and cost-saving advantage possible with gatifloxacin, levofloxacin, and moxifloxacin, allows the switching of patients from intravenous to oral therapy without having to change the dosage regimen or class of antibiotics. In addition to shortening the hospital stay and reducing the risk of venous complications, step-down therapy has been shown to cut hospital drug costs by 40% and hospitalization costs by 20%.

In vitro activity of fleroxacin against multiresistant gram-negative bacilli isolated from patients with nosocomial infections

In order to evaluate the in vitro activity of fleroxacin against nosocomial gram-negative organisms, 263 multiresistant gram-negative bacilli (203 Enterobacteriaceae and 60 non-fermenting gram-negative bacilli) were isolated from adult patients with nosocomial infections. The different patterns of resistance to eight different antimicrobial agents (ampicillin, carbenicillin, piperacillin, cephalothin, cefamandole, ceftazidime, gentamicin and amikacin) were determined by minimum inhibitory concentration (MIC), using the agar dilution method. The most prevalent multiresistant species isolated were Klebsiella pneumoniae (28.9%), Escherichia coli (24%) and Pseudomonas aeruginosa (12.2%). All these bacterial strains showed three to five resistance patterns to at least three different antibiotics. Resistance to ceftazidime was observed in at least one of the resistance patterns of isolated bacteria. The activity of fleroxacin against multiresistant enteric bacteria was excellent; these strains showed a susceptibility of 79-100%. The susceptibility of P. aeruginosa to antipseudomonal agents was low; however, the activity of fleroxacin against these strains was higher than 60% (MIC < or = 2 microg/ ml), broadly comparable with ciprofloxacin. The resistance to fluoroquinolones detected in this study was no cause for alarm (3%). Consequently, fleroxacin maintains a remarkable activity against Enterobacteriaceae and remains highly active against other gram-negative bacilli. Nevertheless, actions directed at preventing or limiting resistance will be crucial to maintain the viability of fluoroquinolones as important therapeutic agents.

In vitro activity of BAY 12-8039, a new fluoroquinolone, against species representative of respiratory tract pathogens

The in vitro antibacterial activity of BAY 12-8039, a novel 8-methoxy-quinolone, was compared with those of other quinolones, amoxicillin/clavulanate, cefuroxime and erythromycin against species commonly implicated in respiratory tract infections as well as viridans group streptococci. The new compound was highly active against methicillin-susceptible staphylococci (MIC90 0.125 microgram/ml), penicillin-susceptible and penicillin-resistant pneumococci (MIC90 0.5 and MIC50 0.25 microgram/ml, respectively), penicillin-susceptible and penicillin-resistant viridans group streptococci (MIC90 0.5 and 0.25 microgram/ml, respectively), group A streptococci (MIC90 0.25 microgram/ml), M. catarrhalis (MIC90 0.125 microgram/ml) and H. influenzae (MIC90 0.063 microgram/ml), irrespective of beta-lactamase production. It was, however, less active against methicillin-resistant staphylococci (MIC50 and MIC90, 2 and 4 micrograms/ml, respectively). The new compound demonstrated bactericidal activity at concentrations 2, 4, 8 times the MIC against representative isolates of the above collection. At a concentration of eight times the MIC, the frequency of spontaneous resistance ranged from 2.5 x 10(-7) to < 4 x 10(-8). These results suggested that BAY 12-8039 would be a promising agent for the eradication of respiratory tract pathogens and that clinical trials assessing its efficacy for the management of infections caused by these organisms are warranted.

Ciprofloxacin-resistant Escherichia coli emerging in a rehabilitation medical center

A retrospective review of laboratory records from 1988 to 1996 has shown an increased rate of ciprofloxacin-resistant (cip(r)) Escherichia coli in our rehabilitation center. Resistance increased from 0.6% in 1989 to 5.9% in 1996. Of 7870 E. coli strains isolated during this period, 257 cip(r)-E. coli were recovered from 257 patients. The majority (96%) of these resistant strains were isolated from the urine samples. One hundred and twenty strains of cip(r)-E. coli were also resistant to four other fluoroquinolones. MICs ranging from 64 to 512 micrograms/mL were observed in 75% of the strains and > or = 1028 micrograms/mL in 6.4% of the strains. Resistance to ciprofloxacin was due to possible mutations in topoisomerase gyrA.

Susceptibility of ciprofloxacin-resistant staphylococci and enterococci to trovafloxacin

The susceptibilities of clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) and enterococci obtained over a 13-year period were tested for trovafloxacin, a new fluoroquinolone, and ciprofloxacin. For MRSA, MIC50 values for trovafloxacin increased from 0.03 microgram/ml to 1 microgram/ml from 1984-1985 to 1995-1996, but were lower than those noted for ciprofloxacin, which increased from 0.25 microgram/ml to > 8 micrograms/ml during the same period. Trovafloxacin also showed lower MIC50 values (0.12-0.25 microgram/ml) than ciprofloxacin (MIC50 of 0.5-1 microgram/ml) for E. faecalis isolates from 1985 through 1991, but against E. faecium and E. faecalis isolated in 1995-1996, the MIC50 values for both trovafloxacin and ciprofloxacin were 2 micrograms/ml and the MIC90 values were > or 8 micrograms/ml. Thus, cross-resistance between fluoroquinolones was shown for both enterococci and MRSA. Whether the greater intrinsic activity of trovafloxacin might allow its use in treating MRSA and enterococcal infections remains to be seen.

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.