Comparative activity of ofloxacin with reference to bacterial strains isolated in in-patients and out-patients

Retinal toxicity of liposome-incorporated and free ofloxacin after intravitreal injection in rabbit eyes

BACKGROUND

Ofloxacin (OFLX) is a fluoroquinolone-antibiotic with a broad antimicrobial spectrum that may have a potential role in the treatment of bacterial endophthalmitis. However, its elimination half life after intravitreal injection is short. To prolong the intravitreal antibacterial level OFLX was incorporated into liposomes. This study was performed to investigate the retinal toxicity of liposome-incorporated and free OFLX.

MATERIALS AND METHODS

OFLX was incorporated into multilamellar large vesicles. 0.1 ml of this suspension (= 180.2 microg OFLX) was injected into the midvitreous of rabbit eyes (n = 6). Free OFLX in doses of 100 microg, 500 microg and 1,000 microg was injected into the midvitreous of a second group of rabbit eyes (n = 18). The other eye served as a control and received empty liposomes or normal saline solution, respectively. Before injection and at the end of follow-up an ERG was obtained. After a follow-up of 1 day, 14 and 28 days the animals were perfused with glutaraldehyde and the eyes were examined by light- and transmission electron microscopy.

RESULTS

The ERG as well as the histologic studies did not reveal any pathological changes after injection of liposome-incorporated OFLX compared to the control eyes. Significant reduction of the ERG was observed after 500 microg free OFLX in 2 out of 6 eyes after 1 and 14 days, respectively, and in 2 eyes 1 day after 1,000 microg free OFLX. Three days after injection of 1,000 microg OFLX the retina showed focal destruction in 1 out of 6 eyes. In another eye with the same dose 14 days after injection the photoreceptor outer segments showed disorganisation.

CONCLUSION

This study shows that liposome-incorporated OFLX did not have any retinal toxicity in this animal model. Free OFLX appears to have no retinal toxicity in rabbit eyes at a dose of 100 microg after intravitreal injection. Injection of higher doses resulted in ERG changes and marked retinal damage.

Community-acquired urinary tract infection in adults: a hospital viewpoint

The clinical and epidemiologic spectrum of 175 cases of community-acquired urinary tract infection (UTI) were evaluated at a university hospital. Patients were grouped in five different categories of which complicated UTI was the most common (39%). Bacteraemia was detected in eight patients (18%) of this group and in five (12%) with acute uncomplicated pyelonephritis. A single organism was isolated in 166 cases (95%). The rate of Escherichia coli bacteriuria ranged from 60% (asymptomatic bacteriuria) to 94% (uncomplicated cystitis). Of the 184 isolates, 92% were susceptible to ciprofloxacin and significantly high rates of resistance were found for ampicillin, cefazolin, cefuroxime, and co-trimoxazole. Isolates causing uncomplicated UTI had significantly high rates of resistance to ampicillin, amoxycillin-clavulanate and co-trimoxazole and those causing complicated UTI, had significantly high rates of resistance to most oral antibiotics tested, except quinolones and nitrofurantoine. Community-acquired UTI requiring hospital evaluation occurs in a complex group of patients, and current patterns of antibiotic resistance make it difficult to suggest empiric oral treatments in this setting.

Ofloxacin clinical pharmacokinetics

Ofloxacin is a new fluoroquinolone with a spectrum of activity similar to other fluoroquinolones with activity which includes Chlamydia trachomatis, Mycobacterium spp., Mycoplasma spp. and Legionella pneumophila. Through its additional mechanisms of action, ofloxacin may be less susceptible to the development of resistance from Staphylococcus aureus commonly seen with currently available fluoroquinolones. The impact of these findings cannot be evaluated without further clinical experience. The pharmacokinetics of ofloxacin are characterised by almost complete bioavailability (95 to 100%), peak serum concentrations in the range of 2 to 3 mg/L after a 400mg oral dose and an average half-life of 5 to 8h. In comparison with other available quinolones, elimination is more highly dependent on renal clearance, which may lead to more frequent dosage adjustments in patients with impaired renal function. Ofloxacin appears less likely to affect the pharmacokinetics of drugs (e.g. theophylline) which commonly interact with fluoroquinolones such as ciprofloxacin and enoxacin. The properties of ofloxacin make it a therapeutic alternative to currently available fluoroquinolones.

Concentration of ofloxacin and ciprofloxacin in human semen following a single oral dose

A single oral dose of ofloxacin (400 mg.) or ciprofloxacin (500 mg.) was administered to each of 40 men. The mean concentrations of ofloxacin in semen exceeded those of ciprofloxacin at 1 hour (p = 0.035) and 24 hours (p = 0.028), while the levels of the 2 drugs at 2 and 4 hours were comparable. Semen concentrations of ofloxacin but not ciprofloxacin exceeded the reported minimal inhibitory concentration of Enterobacteriaceae, Chlamydia trachomatis and genital Mycoplasma species 24 hours after dosage.

Antimicrobial susceptibility in gram-negative bacteremia: are nosocomial isolates really more resistant?

Bloodstream isolates of gram-negative aerobic bacilli from nosocomial infections are more likely to be resistant to antimicrobial agents than isolates from community-acquired cases are. It is not clear, however, how much this is due to the markedly different distribution of organisms in the two groups. We compared the susceptibilities of organisms of a given species which caused community-acquired bacteremia with the susceptibilities of isolates from nosocomial cases. Nine antimicrobial agents were tested against 1,077 isolates which were obtained during a 4-year nonepidemic period. Marked differences in crude rates of resistance were noted for all isolates from nosocomial cases versus all isolates from cases acquired in the community. When results were adjusted for the different organism distributions in the two groups, statistically significant differences were found for only six drug-organism pairs; in each of these, resistance rates were higher in nosocomial isolates. However, when results were further adjusted for the effect of multiple analyses, no significant differences were seen. The major factor leading to the greater prevalence of antimicrobial resistance in our hospital organisms was the markedly different distribution of organisms in the nosocomial and community-acquired groups. For individual organisms, greater resistance in nosocomial strains was confined to certain drugs. Factors that influence differences in organism distribution may not be solely the result of antimicrobial use.

Ofloxacin: a review

Ofloxacin is a new fluorinated quinolone antibiotic with a broad spectrum of activity against a variety of gram-positive and -negative bacteria including Enterobacteriaceae, Pseudomonas aeruginosa, and methicillin-resistant Staphylococcus aureus. In addition, ofloxacin has significant activity against Neisseria gonorrhoeae, Chlamydia trachomatis, and Mycobacterium tuberculosis and this may give rise to new indications for the class of quinolone antibiotics. Clinical trials to date have demonstrated the efficacy of ofloxacin in the treatment of lower respiratory tract infections, urinary tract infections, and sexually transmitted diseases. Adverse effects to ofloxacin are usually mild and include gastrointestinal, central nervous system, and hypersensitivity reactions. Significant drug interactions with ofloxacin have not been reported.

Relative bioavailability of ofloxacin tablets in comparison to oral solution

Single oral doses of solution and tablet preparations of 300 mg ofloxacin were given to 13 healthy male volunteers in an open, randomized crossover study. Concentrations of the unchanged drug were monitored at various times in serum and urine, over 28 hours and 48 hours, respectively. Each dose was followed by a 1-week washout period. Drug concentrations were measured both by a specific high pressure liquid chromatography (HPLC) method and a microbiological assay. A linear distribution independent regression analysis for method comparisons was calculated and good agreement between the two methods was found. Medians of maximum serum concentrations (Cmax) of ofloxacin after oral solution and tablet form were 5.0 mg/l and 3.5 mg/l, respectively. The times to maximal serum concentration (tmax) were 0.5 hr and 1.0 hr, respectively. The lower Cmax and later tmax after the tablet form were both statistically (p less than 0.05) different when compared to the corresponding values after the oral solution. However, the areas under the serum concentration-time curves (AUC0-28), as also the urinary recoveries did not differ significantly, showing that only the speed of absorption, but not the bioavailability of the tablet is changed in comparison to the oral solution form. Long-lasting, clinically relevant urine concentrations of ofloxacin were observed after both forms until the last collecting fraction (36 to 48 hours after medication). General tolerability was good; no side-effects were reported.

The effect of food on the pharmacokinetics of ofloxacin

After oral administration of a single dose of ofloxacin (300 mg), with and without a standard breakfast, to 12 healthy male volunteers in an open, randomized crossover study, concentrations of the unchanged drug were estimated at various times in serum and urine, over 28 hours and 48 hours, respectively. Each dose was followed by a wash-out period of 1 week. Ofloxacin concentrations were determined using high pressure liquid chromatography (HPLC): parallel determinations using a microbiological assay were in close agreement. Maximum serum concentrations (Cmax) of ofloxacin, after fasting and with breakfast, respectively, were 3.7 and 3.1 micrograms/ml (HPLC, median values). The corresponding areas under the serum concentration-time curves (AUC0-28) were 29.9 and 24.5 micrograms/ml. The lower values of Cmax and AUC0-28 found after food intake were statistically significant (p less than 0.05) but not clinically relevant when compared to the fasting values. Time to reach Cmax and terminal elimination half-life (t1/2 beta) were not significantly affected by food intake: t1/2 beta was calculated as 5.3 and 5.9 hours (HPLC, median values), fasting and with breakfast, respectively. Urinary recovery (after 48 hours: 72% and 74%, respectively) was also not significantly affected by food intake, and urinary concentrations of ofloxacin remained far above 1 microgram/ml, i.e. above the minimum inhibitory concentration (MIC90) for most bacterial strains, for at least 48 hours after drug administration. General tolerability was good; no side-effects were reported.