In vitro studies of ciprofloxacin and survey of resistance patterns in current isolates

Fluoroquinolone Therapy in Staphylococcus aureus Infections: Where Do We Stand?

AIM

The study aimed to evaluate the utility of various commonly used fluoroquinolones against Staphylococcus aureus isolates.

MATERIALS AND METHODS

A total of 250 isolates of S. aureus were studied from different clinical specimens like blood, pus, wound swabs, sputum, ear swabs, and body fluids between November 2009 and December 2011. All the isolates were tested for their susceptibility to fluoroquinolones and other antimicrobial agents by Kirby-Bauer disc diffusion method using criteria of standard zone of inhibition. Methicillin-resistant S. aureus (MRSA) detection was done by cefoxitin disk diffusion method. The MRSA isolates were tested for minimum inhibitory concentration (MIC) to vancomycin by E-test strips. All the MRSA strains were sent to National Staphylococcal Phage-typing Centre, Maulana Azad Medical College, New Delhi for phage typing.

RESULTS

A total of 107 strains of S. aureus (42.8%) were detected as MRSA. Multidrug resistance was observed among the MRSA strains more commonly than among the MSSA stains. Among the fluoroquinolones, maximum resistance in MRSA was seen to ciprofloxacin (92.5%), followed by ofloxacin (80.4%). None of the S. aureus isolates showed resistance to vancomycin and linezolid. The MICs of vancomycin for the MRSA tested ranged from 0.5 to 2 μg/ml. Phage typing pattern of 107 MRSA isolates revealed that 37 (34.6%) MRSA isolates were nontypeable and 70 (65.4%) were typeable.

CONCLUSION

Ciprofloxacin can no longer be used in empirical therapy against MRSA infections. Use of other members of fluoroquinolone should be limited only to those strains that show laboratory confirmation of their susceptibility. Vancomycin remains the drug of choice to treat MRSA infections.

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.

Pseudomonas infections in Tohid Burn Center, Iran

Burn injury is a major public health problem in many areas of the world. Pseudomonas aeruginosa is one of the most common causes of burn wound infection in burn patients. Septicemia due to this organism is a major cause of mortality among burn patients. This study analyzed P. aeruginosa infections in the Tohid Burn Center in Tehran during 1995-1997 in order to estimate their frequency, antibiotic susceptibility and their role in burn morbidity. Among 2122 patients who were admitted during this study period, 3365 bacterial strains were isolated and the frequency of P. aeruginosa was 73.9%. This was followed by Staphylococcus aureus (9.1%) and other organisms (17%) in frequency. The frequency of P. aeruginosa resistant to gentamicin, carbenicillin, co-trimoxazole, ceftizoxime and tetracycline was over 95% and resistance to amikacin which was 49% in 1995, increased to 90% in 1997. With the introduction of ciprofloxacin at our burn center, the frequency of P. aeruginosa resistance increased from 45% in 1995, to 82% in 1997. P. aeruginosa was found more frequently in the ICU than in the wards. These findings show that P. aeruginosa remains the leading cause of nosocomial infections in our burn center. It is necessary to introduce urgent measures for restriction of the spread of P. aeruginosa infections in our burn center.

Interpretive criteria and quality control parameters for testing of susceptibilities of Haemophilus influenzae and Streptococcus pneumoniae to trimethoprim and trimethoprim-sulfamethoxazole. The Antimicrobial Susceptibility Testing OC Group

Two hundred twenty-eight strains of Haemophilus influenzae and 234 strains of Streptococcus pneumoniae were tested by broth microdilution and disk diffusion methods for susceptibility to trimethoprim (TMP) and TMP-sulfamethoxazole (SMX) to evaluate proposed criteria. Data are presented to support the proposed TMP MIC breakpoints of < or = 2.0 micrograms/ml for susceptibility and > or = 4.0 micrograms/ml for resistance for both species and TMP-SMX MIC breakpoints of < or = 2.0-38 micrograms/ml for susceptibility and > or = 4.0-76 micrograms/ml for resistance. Corresponding zone diameter breakpoints for H. influenzae for both drugs are proposed: < or = 10 mm = resistant; > or = 16 mm = susceptible. A 10-laboratory study documented reproducibility of such tests with standard control strains. The following control limits are proposed for tests of H. influenzae ATCC 49247 against TMP; MIC, 0.12 to 0.5 microgram/ml; zone diameter, 27 to 33 mm. The current limits for TMP-SMX were confirmed. For tests of S. pneumoniae ATCC 49619, MICs of TMP were 1.0 to 4.0 micrograms/ml and the current TMP-SMX MIC range was confirmed. Disk susceptibility tests of either drug against pneumococci were not reproducible, and consequently neither quality control limits nor interpretive criteria could be established. Endpoint interpretation and lot-to-lot variability in Mueller-Hinton agars were significant factors leading to interlaboratory variability.

High-level fluoroquinolone resistance in Streptococcus pneumoniae requires mutations in parC and gyrA

The mechanism of high-level fluoroquinolone resistance was studied in strains of Streptococcus pneumoniae, either selected in vitro or isolated from clinical samples. By using DNA from these high-level-resistant strains, low-level-resistant transformants (MIC of pefloxacin, > or = 32 micrograms/ml; MIC of ciprofloxacin, 4 micrograms/ml; MIC of sparfloxacin, 0.50 micrograms/ml) were obtained at high frequencies (ca.10(-2)), while high-level-resistant transformants (MIC of pefloxacin, > or = 64 micrograms/ml; MIC of ciprofloxacin, 16 to 64 micrograms/ml; MIC of sparfloxacin, > or = 8 micrograms/ml) were obtained only at low frequencies (ca.10(-4)). This suggested that mutations in at least two unlinked genes were necessary to obtain high-level resistance. Low-level resistance was associated with ParC mutations (change from Ser to Tyr at position 79 [Ser79Tyr], Ser79Phe, or Asp83Gly). ParC mutations were associated, in high-level-resistant strains and transformants, with alterations in the quinolone resistance-determining region of GyrA (Ser84Tyr, Ser84Phe, and/or Glu88Lys). Low-level resistance was shown to be necessary for expression of the gyrA mutations. No mutation in the region corresponding to the quinolone resistance-determining region of GyrB and no alteration of drug accumulation were found.

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.

Multicenter Spanish study of ciprofloxacin susceptibility in gram-negative bacteria. The Spanish Study Group on Quinolone Resistance

The susceptibility of 2,426 gram-negative bacteria obtained from 18 Spanish hospitals to ciprofloxacin was evaluated. Among different medical centers, susceptibility to ciprofloxacin ranged from 83 to 100% for Enterobacteriaceae, from 35 to 100% for Pseudomonas aeruginosa, from 0 to 100% for Xanthomonas maltophilia, Acinetobacter spp. and other gram-negative non-fermenting bacilli, and from 33 to 100% for Campylobacter spp. All clinical isolates of Haemophilus influenzae, Moraxella catarrhalis and Neisseria gonorrhoeae were susceptible to ciprofloxacin.

Penetration of ciprofloxacin into the human pancreas

The aim of this study was to determine the concentrations of ciprofloxacin in human pancreatic tissue and juice. Concentrations were measured by high-pressure liquid chromatography (HPLC). Two hundred mg of ciprofloxacin were administered as a short i.v. infusion (30 min). The median ciprofloxacin concentrations 140 min (median) after the start of infusion in pancreatic tissue as well as in pancreatic juice were 0.9 mg/kg (mg/l). The penetration ratio was 1.0 for pancreatic tissue and 0.83 for pancreatic juice. With regard to the minimal inhibitory concentrations (MIC) for the respective bacteria, ciprofloxacin seems to be an appropriate drug for the treatment of septic complications in necrotizing pancreatitis. Future clinical trials are necessary to prove this assumption.

Increased resistance to quinolone in Catalonia, Spain

From 1989 to 1991, the level of resistance to ciprofloxacin in our hospital increased from 0.47% to 6.7% in opportunistic Enterobacteriaceae, from 9.9% to 16% in Pseudomonas aeruginosa and from 8.27% to 31.8% in Campylobacter jejuni-coli. We also observed an increase in quinolone consumption from 1.1 in 1989 to 1.5 defined daily doses per 1000 inhabitants per day in 1991.

In vitro activity of sparfloxacin compared with those of five other quinolones

The in vitro activity of sparfloxacin, a new difluorinated quinolone, was evaluated against 857 gram-positive and gram-negative clinical isolates and compared with those of ciprofloxacin, norfloxacin, ofloxacin, fleroxacin, and lomefloxacin. The MIC of sparfloxacin for 90% of the members of the family Enterobacteriaceae tested was 0.5 microgram/ml (range, 0.06 to 4.0 micrograms/ml); only for members of the genera Serratia, Citrobacter, and Providencia were MICs above 1 microgram/ml. Some 90% of Pseudomonas aeruginosa isolates were inhibited by 8 micrograms of the drug per ml. The MICs for 90% of Staphylococcus spp. and Enterococcus faecalis were 0.12 and 2 micrograms/ml, respectively. All (100%) Streptococcus pneumoniae strains were inhibited by 0.5 microgram/ml. The inoculum size had little effect on either the MIC or the MBC of sparfloxacin. An increase in the magnesium concentration from 1.1 to 8.4 mM increased the MIC between 2 and 10 times, depending on the genus tested. Sparfloxacin was less active at pH 5. The antibacterial activity of sparfloxacin against gram-positive bacteria was generally higher than those of the quinolones with which it was compared; against Streptococcus pneumoniae, sparfloxacin was four- and eightfold more active than ofloxacin and ciprofloxacin, respectively. The activity of sparfloxacin against gram-negative rods was generally comparable to that of ciprofloxacin except against Enterobacter and Acinetobacter spp., Pseudomonas cepacia, Xanthomonas maltophilia, and Alcaligenes and Flavobacterium spp., against which sparfloxacin was the most active quinolone.