Ocular penetration of topical ciprofloxacin and norfloxacin drops and their effect upon eyelid flora

Bacterial keratitis: identifying the areas of clinical uncertainty

Bacterial keratitis is a common corneal infection that is treated with topical antimicrobials. By the time of presentation there may already be severe visual loss from corneal ulceration and opacity, which may persist despite treatment. There are significant differences in the associated risk factors and the bacterial isolates between high income and low- or middle-income countries, so that general management guidelines may not be appropriate. Although the diagnosis of bacterial keratitis may seem intuitive there are multiple uncertainties about the criteria that are used, which impacts the interpretation of investigations and recruitment to clinical studies. Importantly, the concept that bacterial keratitis can only be confirmed by culture ignores the approximately 50% of cases clinically consistent with bacterial keratitis in which investigations are negative. The aetiology of these culture-negative cases is unknown. Currently, the estimation of bacterial susceptibility to antimicrobials is based on data from systemic administration and achievable serum or tissue concentrations, rather than relevant corneal concentrations and biological activity in the cornea. The provision to the clinician of minimum inhibitory concentrations of the antimicrobials for the isolated bacteria would be an important step forward. An increase in the prevalence of antimicrobial resistance is a concern, but the effect this has on disease outcomes is yet unclear. Virulence factors are not routinely assessed although they may affect the pathogenicity of bacteria within species and affect outcomes. New technologies have been developed to detect and kill bacteria, and their application to bacterial keratitis is discussed. In this review we present the multiple areas of clinical uncertainty that hamper research and the clinical management of bacterial keratitis, and we address some of the assumptions and dogma that have become established in the literature.

Ocular toxicity of fluoroquinolones

The ocular toxicity of fluoroquinolones and the risks of their use in the treatment of ocular infection were reviewed. Systematic identification, selection, review and synthesis of published English-language studies relating to fluoroquinolone use and safety in animals and humans was conducted. Although not free of complications, fluoroquinolones are generally safe when used to treat ocular infection. Ocular toxicity appears to be dose-dependent and results from class-effects and specific fluoroquinolone structures. Phototoxicity and neurotoxicity have been reported, and toxic effects on ocular collagen may be associated with Achilles tendinopathy. Corneal precipitation may provide an advantageous drug depot but delay healing and result in corneal perforation in approximately 10% of cases. Although human toxicity studies are limited, the current recommended dose for intracameral injection of ciprofloxacin is less than 25 microg. Intravitreal injections of ciprofloxacin 100 microg, ofloxacin 50 microg/mL, trovafloxacin 25 microg or less, moxifloxacin 160 microg/0.1 mL or less and pefloxacin 200 microg/0.1 mL are considered safe.

Ciprofloxacin and ofloxacin aqueous humor concentrations after topical administration in dogs undergoing cataract surgery

OBJECTIVE

To determine if preoperative topical administration of ciprofloxacin or ofloxacin results in aqueous humor drug concentrations that exceed the MIC(90) of common ocular contaminants in dogs undergoing cataract surgery.

PROCEDURES

Twelve dogs were treated with topical 0.3% ciprofloxacin and 13 dogs with topical 0.3% ofloxacin once the night before surgery, and then with 1 drop of ciprofloxacin or ofloxacin every 15 min for 2 h immediately before surgery. Aqueous humor samples were taken from each eye immediately before the incision was made and frozen at -70 degrees C. First eye samples (S1) were taken closer to the time of topical treatments than second eye samples (S2). Samples were analyzed by high performance liquid chromatography (HPLC) at the North Carolina State University (NCSU) Clinical Pharmacology laboratory.

RESULTS

In ciprofloxacin patients, S1 concentrations were 0.03-0.69 (0.17 median) microg/mL, and S2 concentrations were 0.09-0.95 (0.36 median) microg/mL. Aqueous humor concentrations did not exceed the MIC90 of Streptococcus sp. Few eyes (1/12 OU) exceeded the MIC90 for Staphylococcus sp. or Corynebacterium sp.; moderate numbers (5/12 S1; 8/12 S2) exceeded the MIC90 for E. coli. In ofloxacin patients, S1 concentrations were 0.48-2.81 (1.05 median) microg/mL, and S2 concentrations were 0.45-3.63 (1.30 median) microg/mL. Although few eyes (<or=2/13 OU) exceeded the MIC90 for Streptococcus sp. or Corynebacterium sp., moderate numbers (7/13 S1, 9/13 S2) exceeded the MIC90 for Staphylococcus sp. and most eyes (12/13 OU) exceeded the MIC90 for Bacillus sp. All eyes exceeded the MIC90 for E. coli.

CONCLUSIONS

Ofloxacin has higher corneal penetration and ability to exceed MIC90 of common ocular contaminants than ciprofloxacin, and would be a more appropriate prophylactic choice for canine cataract patients.

Concentrations of levofloxacin, ofloxacin, and ciprofloxacin in human corneal stromal tissue and aqueous humor after topical administration

OBJECTIVE

To evaluate the penetration of commercially available levofloxacin 0.5%, ofloxacin 0.3%, and ciprofloxacin 0.3% topical ophthalmic solutions in human corneal stromal and aqueous humor tissues.

METHODS

A total of 67 patients scheduled to undergo penetrating keratoplasty for treatment of stromal scar or dystrophy, keratoconus, pellucid marginal degeneration, or endothelial disease were enrolled in this prospective, double-blind, 3-center study. To be considered for inclusion, patients had to have an intact corneal epithelium and minimal or no corneal edema (pachymetry < 650 microm). After informed consent was obtained, patients were randomized to receive 1 drop of levofloxacin 0.5%, ofloxacin 0.3%, or ciprofloxacin 0.3% topical ophthalmic solution at approximately 15 and 10 minutes before surgery. Approximately 0.1 mL of aqueous fluid was aspirated by paracentesis through the trephination wound at the onset of surgery, followed by excision of the affected cornea and removal of its epithelium. Specimens were stored frozen at -70 degrees C until assayed by high-performance liquid chromatography.

RESULTS

All 3 fluoroquinolones were well tolerated. A total of 65 corneas and 59 aqueous fluid samples were obtained and assayed. The mean +/- standard deviation corneal concentrations of ciprofloxacin, ofloxacin, and levofloxacin following a 2-drop administration were 9.92 +/- 10.99 microg/g (n = 18), 10.77 +/- 5.90 microg/g (n = 23), and 18.23 +/- 20.51 microg/g (n = 24), respectively. Although corneal stromal levels were highest in the levofloxacin group, the high degree of interpatient variability prevented demonstration of statistically significant differences when compared with ofloxacin (P = 0.377). In contrast, levofloxacin concentrations were approximately twice as high as ciprofloxacin, and this difference reached statistical significance (P = 0.014). The corresponding aqueous humor concentrations of ciprofloxacin, ofloxacin, and levofloxacin were 0.135 +/- 0.231 microg/mL (n = 15), 0.135 +/- 0.111 microg/mL (n = 20), and 0.372 +/- 0.546 microg/mL (n = 24, P < 0.001 versus ciprofloxacin and ofloxacin).

CONCLUSION

The topical administration of all 3 agents was well tolerated in patients undergoing penetrating keratoplasty. Two drops of levofloxacin 0.5% solution results in a 1.7- to 2.7-fold greater penetration into human corneal stromal and aqueous humor tissues than ofloxacin 0.3% or ciprofloxacin 0.3%. The mean intracorneal concentrations of all three agents following 2 drops exceeds the MIC90 for the majority of pathogens causing bacterial keratitis. Topical levofloxacin appears to offer pharmacokinetic and pharmacodynamic advantages over ofloxacin and ciprofloxacin in terms of enhanced transcorneal penetration; however, clinical comparative trials are needed to confirm these relative advantages.

Comparative review of topical ophthalmic antibacterial preparations

The choice of an antibacterial is based on considerations of pharmacodynamic, pharmacokinetic and bacteriological characteristics, risk of selecting resistant mutants, and cost. In this article we review 16 commercially available ophthalmic antibacterial preparations. Fusidic acid and bacitracin are selective for gram-positive bacteria whereas polymyxin B targets gram-negative species. Aminoglycosides and quinolones are broad spectrum antibacterials. The widespread use of an antibacterial increases risks of selecting resistance to it. Acquired resistance is well documented for fusidic acid and rifamycin, and newly described for quinolones. The bioavailability of an antibacterial agent depends on the target bacterial species, the site of infection and the integrity of the haemato-aqueous barrier. Some agents (fusidic acid, quinolones) penetrate the cornea, passing into the anterior chamber of normal eyes at therapeutic concentrations, whereas others (polymixin B, bacitracin) have no penetrating powers and remain at the surface of the eye. Toxicity is mostly manifested by allergic reactions to excipients or active ingredients in topical antibacterial preparations. A few cases of haematological toxicity have brought suspicion on topical chloramphenicol, but the link has yet to be proven. Erythromycin and polymyxin B are probably okay to use as topical applications in pregnant women and nursing mothers. Costs of treatment must be evaluated as a whole (regimen, drug associations). Prices for a bottle of eyedrops may vary 3-fold. The cheapest drugs include chloramphenicol, polymyxin B and gentamicin, the most expensive being fusidic acid and the quinolones.

Use of antimicrobials to prevent postoperative infection in patients with cataracts

Despite the high frequency of cataract surgery, there are still no definitive studies on antibiotic prophylaxis against endophthalmitis after cataract surgery. Most surgeons follow an empiric approach. The results of several recent studies shed additional light on this complex topic. There is better knowledge of the usual source of the infection and the specific organisms incriminated. This review presents some principles of prophylactic treatment and selected literature that addresses the effectiveness of antisepsis, topical preoperative antibiotics, intracameral antibiotics, subconjunctival antibiotics, systemic antibiotics, and postoperative antibiotics. The worldwide problem of antibiotic resistance should temper our approach. Some organizational statements are reviewed, and personal recommendations are offered. Controversy still abounds.

Preoperative gentamicin eye drops and chlorhexidine solution in cataract surgery. Experimental and clinical results

PURPOSE

1) To evaluate the effects on the conjunctival flora of gentamicin ophthalmic eye drops 0.3%, given four times in 45 minutes, and a conjunctival rinse with 10 ml chlorhexidine 0.05% solution. 2) To investigate retrospectively the rate of endophthalmitis after cataract operations when these antimicrobials were applied preoperatively.

METHODS

Seventy-six patients undergoing standard phacoemulsification operations were enrolled in the experimental part of the study. Cultures were taken preoperatively, 5 minutes after prophylaxis with either chlorhexidine or gentamicin. To assess the combined effects of chlorhexidine and gentamicin, cultures were taken after the cataract operation. Hospital charts were reviewed for cases of endophthalmitis in 1994 and 1995, when this prophylactic protocol was used at the St Erik's cataract surgery department.

RESULTS

The conjunctival microflora was significantly suppressed by chlorhexidine rinsing alone (p = 0.001), while no other significant anti-bacterial effects were observed with the experimental prophylaxis. The endophthalmitis rate was 32/12. 806 operations (0.25%).

CONCLUSIONS

Topical rinsing with chlorhexidine solution suppresses conjunctival flora in the short term. Combined topical chlorhexidine and gentamicin prophylaxis does not eliminate postoperative endophthalmitis caused by gram-positive bacteria.

Subretinal fluid levels of topical, oral, and combined administered ciprofloxacin in humans

AIMS

To investigate the subretinal fluid (SRF) penetration of ciprofloxacin following topical, oral, and combined administration.

METHODS

34 patients undergoing conventional retinal reattachment surgery were randomly assigned to three groups. Twelve patients received topical ciprofloxacin, 11 patients received oral ciprofloxacin, and the other 11 patients received combined drug administration. SRF drug level was measured by using high performance liquid chromatography method.

RESULTS

The highest drug concentrations of all tested modes were attained following combined administration and lowest following topical administration (p<0.001). The SRF drug concentration following oral administration was also significantly higher than that of topical administration (p<0.001). Concentrations after oral and combined administration did not differ significantly (p = 0.217).

CONCLUSIONS

Topical ciprofloxacin can penetrate SRF. Ocular bioavailability of ciprofloxacin in SRF after oral and combined administration is equivalent.

The effects of prolonged acute use and inflammation on the ocular penetration of topical ciprofloxacin

PURPOSE

To study the aqueous and vitreous penetration of ciprofloxacin after prolonged acute topical administration and to investigate the effects of inflammation on drug penetration.

METHODS

A standardized model of intraocular infection after penetrating injury was made in the right eyes of eight rabbits. The intact left eyes were maintained as the control. Two drops of ciprofloxacin 0.3% eyedrops were instilled topically every 1 h for 7 h to all eyes of the rabbits. Aqueous and vitreous samples (100 microl) were obtained half an hour after the last drop. Instillation was continued for 7 h more and samples were obtained as before. Drug concentrations were measured using HPLC.

RESULTS

The mean aqueous humor levels of ciprofloxacin were: in control eyes 1.31 +/- 0.78 microg/ml after 7 h and 1.85 +/- 1.69 microg/ml after 14 h of instillation: in inflamed eyes 2.18 +/- 1.02 microg/ml after 7 h and 2.91 +/- 2.12 microg/ml after 14 h. The mean vitreous humor levels were: in control eyes 0.65 +/- 0.44 microg/ml after 7 h and 0.72 +/- 0.8 microg/ml after 14 h of instillation; in inflamed eyes 0.67 +/- 0.77 microg/ml after 7 h and 1.01 +/- 0.43 microg/ml after 14 h. However, the differences among the groups were not significant (P > 0.05).

CONCLUSIONS

Ciprofloxacin penetration into aqueous humor was higher in 14-h topical application than that for 7 h. Inflammation increased the penetration of topical ciprofloxacin into aqueous while administered for 7 h and into both aqueous and vitreous humor while administered for 14 h. c

Pharmacokinetics of ciprofloxacin in the human eye: a clinical study and population pharmacokinetic analysis

Ciprofloxacin, a fluoroquinolone antibiotic active against a wide variety of bacteria, is one of a few antibiotics which enters the human eye after oral administration. However, little is known about its pharmacokinetics in the human eye. One or two oral doses of 750 mg of ciprofloxacin (at a 12-h interval) were administered to 48 patients at various times prior to ocular surgery. Clotted blood, aqueous, and vitreous were collected at surgery, and the concentrations of ciprofloxacin were assayed by high-performance liquid chromatography. Our data were combined with those of others, and a population pharmacokinetic analysis was conducted. The concentrations of ciprofloxacin in both aqueous and vitreous were lower than those in serum and peaked at a later time. The pharmacokinetics of ciprofloxacin in aqueous and vitreous were fitted to a compartmental model in which the antibiotic was transferred into and out of the two compartments (aqueous and vitreous) by first-order processes. Population pharmacokinetic software, P-Pharm, was used to calculate the mean half-lives of the loss of ciprofloxacin from aqueous and vitreous, which were 3.5 and 5.3 h, respectively. At steady state, the mean ratios of then concentrations in aqueous and vitreous to the concentrations in serum were 23 and 17%, respectively. After the administration of one or two doses of 750 mg of ciprofloxacin, the concentrations in both aqueous and vitreous in a number of patients were lower than the MICs at which 90% of isolates are inhibited (0.5 mg/liter) for common intraocular bacterial pathogens. Simulations of concentrations in the eye after the administration of higher doses (1,500 mg of ciprofloxacin as a single dose, two doses of 750 mg 2 h apart, and 750 mg every 6 h) indicated that in approximately 20% of patients the concentrations would still be below 0.5 mg/liter. Although oral ciprofloxacin may be a beneficial adjunctive therapy, the use of oral ciprofloxacin alone may not be adequate for perioperative prophylaxis or for treatment of bacterial endophthalmitis.

Treatment of ocular infections with topical antibacterials

Topically applied ophthalmic antibacterial preparations are widely used in the treatment of patients with superficial ocular infections. In addition, they are frequently used to augment treatment for intraocular infection administered systemically or via local instillation. Direct application delivers high concentrations of antimicrobial agents to the surface of the eye conveniently, quickly and with minimal systemic exposure to the agent. However, antibacterials are rapidly dissipated from the tear film and intraocular penetration of topical antibacterial agents is generally poor, necessitating intensive application for successful treatment of corneal infections. Therapeutic concentrations are rarely achieved at other sites in the eye. This article reviews what is known of the pharmacokinetics of topical ocular agents and how this information can be used to optimise ocular persistence and penetration and minimise systemic absorption of antibacterials. A review of the features of the most commonly employed topical antibacterials suggests that for the treatment of uncomplicated bacterial conjunctivitis there is little difference between the various agents in terms of clinical efficacy, although chloram-phenicol should be used with care because of its potential haematological toxicity. Carefully considered therapy is imperative for bacterial keratitis; fortified beta-lactam/aminoglycoside combinations are often used for these infections. The fluoroquinolones appear promising, but caution is necessary in treating keratitis of unknown aetiology with these agents alone because of inherent and emerging acquired resistance among Gram-positive bacteria.

Penetration of topically applied ciprofloxacin, norfloxacin and ofloxacin into the aqueous humor of the uninflamed human eye

This study was undertaken to compare aqueous humor penetration of topical 0.3% ciprofloxacin, 0.3% norfloxacin and 0.3% ofloxacin in 63 patients undergoing cataract surgery. The patients were divided into two groups. Group 1 (long-term treatment) involved 30 patients undergoing cataract extraction who received either 0.3% ciprofloxacin, 0.3% norfloxacin or 0.3% ofloxacin topical drops. Each patient was preoperatively given a single drop per hour six times. At the time of surgery, 0.1 ml aqueous fluid was aspirated from the anterior chamber and immediately stored at -70 degrees C. Topically applied ciprofloxacin, ofloxacin and norfloxacin achieved mean aqueous humor levels of 2.80 +/- 1.07, 2.95 +/- 1.19 and 1.50 +/- 0.48 micrograms/ml respectively. There was no statistically significant difference in intraocular mean aqueous levels of ciprofloxacin versus ofloxacin. Topical ciprofloxacin and ofloxacin achieved mean aqueous humor levels significantly higher than norfloxacin (p < 0.001 and p < 0.0008 respectively). Group 2 (short-term treatment) involved 33 patients undergoing cataract extraction who received 0.3% ciprofloxacin, 0.3% ofloxacin and 0.3% norfloxacin topical drops. These patients were given one drop at 90 minutes and one drop 30 minutes preoperatively. At the time of surgery, 0.1 ml aqueous fluid was aspirated from the anterior chamber and immediately stored at -70 degrees C. Topically applied ciprofloxacin, ofloxacin and norfloxacin achieved mean aqueous humor levels of 1.11 +/- 0.50, 1.50 +/- 0.62 and 1.20 +/- 0.43 micrograms/ml respectively. There was no statistically significant difference in intraocular mean aqueous humor levels of ofloxacin versus norfloxacin and ciprofloxacin versus norfloxacin. Topical ofloxacin achieved a significantly higher mean aqueous humor level than ciprofloxacin (p < 0.03). All levels were above the minimum inhibitory concentrations of ciprofloxacin, ofloxacin and norfloxacin for most of the sensitive organisms.

Widespread ocular use of topical chloramphenicol: is there justifiable concern regarding idiosyncratic aplastic anaemia?

A theoretical but as yet not conclusively proved risk of chloramphenicol induced idiosyncratic aplastic anaemia exists with topical ophthalmic therapy, with the absolute, but highly improbable, maximum risk of death (equalling that of systemic therapy) being 1 in 50,000 to 90,000. To put this in realistic perspective, one must note that the comparable risk of fatal anaphylaxis resulting from penicillin therapy, from any route, is similar at 1 in 100,000. Indeed, it has been noted recently that with more than 200 million ocular chloramphenicol products dispensed in the UK in the past 10 years, only 11 reports (all non-fatal) of suspected topical chloramphenicol induced blood dyscrasia have been reported to the Committee on the Safety of Medicines since 1966. One also has to consider that inadvertent exposure to minute quantities of chloramphenicol (ng/ml) may occur through consumption of livestock that have been treated with chloramphenicol. Broad statements condemning topical chloramphenicol need to be tempered with its proved safety, tolerance, cost, and efficacy while acknowledging an extremely remote risk of the very serious adverse effect of drug induced aplastic anaemia. Risk-benefit assessment is the duty of all prescribing physicians and a decision to prescribe or not prescribe must be made on the basis of personal judgment and an awareness of the statistics in perspective. The only known factor to be associated with vulnerability in the case of topical chloramphenicol is family history. There is no evidence to date that suggests children are any more susceptible than adults.

Antibiotic treatment of ophthalmic infection: new developments

The introduction of quinolones has dramatically altered antibiotic therapy for serious ophthalmic infections. The newer cephalosporins are also playing a more significant role. The recently introduced macrolides, particularly azithromycin, have great potential for treating not only serious infections, but also some of the less serious ones. These new developments are discussed, and the cost implications of new antibiotic treatment on ophthalmology is described.