Ocular penetration of topically applied norfloxacin 0.3% in the rabbits and in humans

The Penetration of Ofloxacin into Human Aqueous Humor Given by Various Routes

This study was designed to measure the concentration of ofloxacin in aqueous humor after topical, oral and intravenous administration in 50 patients undergoing cataract extraction. In Group 1, ofloxacin 0.3% eyedrops were topically instilled ten times and the aqueous humor concentration was 2.73 ± 0.88 μg/ml. In Group 2, ofloxacin 0.3% eyedrops were topically instilled six times and the aqueous humor concentration was 0.84 ± 0.61 μg/ml. Aqueous humor concentration 12 hours after 200 mg oral dose in Group 3, was 0.38 ± 0.12 μg/ml. In Group 4, patients were given ofloxacin as a single intravenous 200 mg dose and the aqueous humor concentration 2 hours after the end of infusion was 0.45 ± 0.11 μg/ml. Concentrations were determined by high performance liquid chromatography (HPLC) with fluorescence detection.

There was a significant difference between Group 1 and the other groups, but not between Group 2 and Groups 3, 4.

It was concluded that ofloxacin penetrates the corneal and the blood-aqueous barriers and can achieve good aqueous levels when given topically and systematically. Ofloxacin can be applied topically for external bacterial infections such as conjunctivitis and keratitis. Systematically administered ofloxacin reached higher levels than the MIC for some bacteria which cause endophthalmitis.

Efficacy of Topical Levofloxacin 0.5% in Treating Levofloxacin-Resistant Pseudomonas aeruginosa-Induced Keratitis

PURPOSE

To evaluate the efficacy of topical levofloxacin 0.5% in treating levofloxacin-resistant Pseudomonas aeruginosa-induced keratitis.

DESIGN

Longitudinal study.

METHODS

The study was conducted in 21 New Zealand White rabbits whose corneas were inoculated with 0.1 mL of 1000 colony-forming units of levofloxacin-resistant P. aeruginosa. After 24 hours, the rabbits were randomized into 3 groups: 9 were treated with levofloxacin 0.5%, 6 were treated with ceftazidime 50 mg/mL, and 6 were treated with a placebo. The rabbits were given a loading dose once every 5 minutes in the first hour and continued to receive a dose once an hour in the next 11 hours. Afterward, 3 rabbits treated with levofloxacin were killed. Their corneas were examined for levofloxacin concentration. The remaining rabbits continued to receive 6 regular doses for 4 more days, each of which was administered at a 2-hour interval. Levofloxacin concentration was examined. Treatment efficacy was evaluated based on 4 clinical characteristics: corneal infiltrate, conjunctival edema, conjunctival injection, and discharge.

RESULTS

All clinical characteristics, except conjunctival edema, improved significantly in rabbits treated with either levofloxacin or ceftazidime, compared to the placebo group. At the last follow-up (120 hours), all clinical characteristics improved significantly in both treatment groups. Mean corneal levofloxacin concentration in the treatment groups was 6.25 (0.32) μg/g, which declined significantly to a mean of 2.15 (1.23) μg/g after another 120 hours.

CONCLUSIONS

Topical levofloxacin 0.5% improved the clinical characteristics of keratitis induced by levofloxacin-resistant P. aeruginosa. Such improvement could be attributed to a high concentration of levofloxacin that was above the minimum inhibitory level.

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.

The effectiveness of a topical antibiotic irrigating solution in a model of staphylococcal keratitis after lamellar keratectomy

PURPOSE

To create a model of Staphylococcus aureus keratitis after lamellar keratectomy; to assess the toxicity of an antibiotic irrigating solution on the corneal stromal bed; and to test the chemotherapeutic effectiveness of a topical antibiotic, both alone and with an antibiotic-containing irrigating solution in preventing S. aureus keratitis after lamellar keratectomy.

METHODS

The right eye of each of 38 rabbits were used in this study. In 18 eyes, a lamellar flap was created with a microkeratome, and an inoculum of S. aureus (either 1,000, 5,000, or 50,000 CFUs) was instilled under each flap; the eyes were examined for signs of infection and inflammation at 24 and 48 hours. In another five eyes, a lamellar flap was created in the same manner and the stromal bed was irrigated with 0.3% ofloxacin; the eyes were assessed for ocular inflammatory changes and evidence of crystalline deposits. Finally, in each of 15 additional eyes, 1,000 CFUs of S. aureus were instilled under a lamellar flap to create experimental infectious keratitis. The keratitis was treated according to three regimens: irrigation of the stromal bed with sterile balanced salt solution; irrigation of the stromal bed with 0.3% ofloxacin, followed by application of topical ofloxacin four times a day; application of topical ofloxacin only, four times a day. Eyes were examined for infection and ocular inflammatory changes at 24 and 48 hours.

RESULTS

Staphylococcus aureus keratitis can consistently be produced under the stromal flap by inoculation of relatively few organisms. Irrigation of the stromal bed with commercial-strength topical ofloxacin does not appear to be toxic to the stromal bed, with no evidence of crystalline precipitates of the antibiotic. In our model of infectious keratitis after lamellar keratectomy, both topical ofloxacin alone and the combination of topical ofloxacin and irrigation of the stromal bed with 0.3% ofloxacin were effective at preventing S. aureus keratitis. However, the combined treatment of antibiotic irrigation plus topical antibiotic was more effective at preventing inflammation than topical ofloxacin alone.

CONCLUSIONS

In this model of S. aureus keratitis after lamellar keratectomy, irrigation of the stromal bed with antibiotic plus topical antibiotic appears to be both safe and effective for preventing infection.

Comparative studies on topical lomefloxacin and ciprofloxacin on ocular kinetic and experimental corneal ulcer

Fluoroquinolones are antimicrobial agents that have a broad spectrum of activity and that are widely used against many of the ocular pathogens responsible for conjunctivitis, blepharitis, corneal ulcers, etc. The aim of our study was to compare the ocular pharmacokinetics of ciprofloxacin (0.3% w/v) and lomefloxacin (0.3% w/v) by HPLC after a single application of 50 microl topically. The study was also extended to compare their efficacy in experimentally-induced corneal ulcers. In ocular kinetic studies, lomefloxacin showed nearly 10 times more ocular bioavailability in aqueous humor as compared to ciprofloxacin. Lomefloxacin showed a Cmax of 1.62 microg/ml at the Tmax of 1 hr whereas ciprofloxacin showed a Cmax of 102.8 ngs/ml at the Tmax of 1 hr. Lomefloxacin was found to have significant efficacy in the healing of Staphylococcus aureus-induced corneal ulcers and associated lesions. Moreover, aqueous formulation oflomefloxacin showed a good compatibility at neutral pH. The results of our study indicate that a suitable treatment regimen with lomefloxacin (0.3%) therapy could be an excellent therapeutic alternative over ciprofloxacin in bacterial keratitis.

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.

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

A double blind, prospective study was undertaken to compare aqueous humour penetration of topical 0.3% norfloxacin and 0.3% ciprofloxacin and their effect upon normal eyelid flora in 39 patients undergoing cataract surgery. Lid swabs were taken before and after six 1 hourly applications of single drops of ciprofloxacin or norfloxacin given before surgery. Aqueous humour was aspirated at surgery and antibiotic concentration assayed using high performance liquid chromatography. The mean aqueous humour concentrations were: ciprofloxacin 220 ng ml-1, norfloxacin 140 ng ml-1. Although this difference was not statistically significant (p = 0.112) the trend demonstrated may be relevant clinically, especially considering the greater activity of ciprofloxacin. Both coagulase negative staphylococcal (p = 0.004) and total bacterial (p = 0.019) lid counts dropped sixfold after ciprofloxacin treatment but the smaller reductions noted after norfloxacin application did not achieve statistical significance (p > 0.1). The reduction of external eye flora experienced with ciprofloxacin suggests that this may be a useful presurgical prophylactic agent.