Bioassays for quantitating ciprofloxacin and tobramycin in aqueous humor

Effects of Fluorosurfactant Structure and Concentration on Drug Availability and Biocompatibility in Water-in-Perfluorocarbon Emulsions for Pulmonary Drug Delivery

The efficacy of inhaled antibiotics is often impaired by insufficient drug penetration into plugged and poorly ventilated airways. Liquid ventilation with perfluorocarbon (PFC) containing emulsified aqueous antibiotics, or antibacterial perfluorocarbon ventilation, could potentially improve treatment of respiratory infections when used as an adjunct therapy to inhaled antibiotics. The molecular structure and concentration of the fluorosurfactant used to stabilize such water-in-PFC emulsions will have significant effects on the efficacy and safety of the resulting treatment. In the present study, emulsions are formulated with tobramycin in the aqueous phase using two different fluorosurfactants (termed FSL-PEG+FSL and FSH-PEG) at varying concentrations (C_fs ). An aqueous gel is used to evaluate the availability of emulsified drug to diffuse into an aqueous interface (such as mucus or biofilm) for varying emulsion formulations. Lastly, the cytotoxicity of the fluorosurfactants is characterized using human alveolar basal epithelial cells. Results showed that tobramycin delivery is reduced at low C_fs due to inadequate drug emulsification and at large C_fs due to hindered drug availability. Thus, maximal delivery occurs at intermediate values of C_fs equal to 2 and 10 mg mL^-1 for the FSH-PEG and FSL-PEG+FSL fluorosurfactants, respectively. The optimal emulsion formulation utilized FSH-PEG and demonstrated improved drug delivery relative to previously used formulations while exhibiting no cytotoxic effect. This work increases understanding of the physical means of pulmonary drug delivery via a water-in-PFC emulsion and represents a critical step in optimizing emulsion formulation for safe and effective treatment.

New drug delivery system for corneal administration of mitomycin-C

PURPOSE

To develop a new corneal release system to deliver optimum amounts of mitomycin-C (MMC) during the perioperative period of photorefractive keratectomy (PRK).

SETTING

Ophthalmos S/A, São Paulo, Brazil.

DESIGN

Experimental study.

METHODS

An in vitro experimental design was developed for studying a new MMC delivery system at a drug concentration of 0.02%. Whatman sterile filter paper disks with a diameter of 8.0 mm were impregnated with MMC solution. After drying, the disks were placed on agar plates seeded with Staphylococcus epidermidis; this was followed by instillation of a drop of sterile water. After 1 minute, the disks were removed and the plates were incubated for 48 hours at 35°C. The mean volume of the drops delivered from regular eyedrop bottles was determined, and the inhibition zone (in millimeters) was correlated with the amount of MMC loaded onto the disks.

RESULTS

Analysis of the inhibition zones produced by MMC indicated that 16 μg was the optimum dose to be incorporated in the disks. The mean volume of a drop delivered from eyedrop bottles was 37.7 μL. One minute after the application of a single drop of a balanced salt solution, the system released an adequate concentration of MMC for PRK.

CONCLUSION

A new delivery system for MMC was successfully developed for application during photorefractive keratectomy.

FINANCIAL DISCLOSURE

Dr. de Souza Lima Filho is the managing director of Ophtalmos S/A. Drs. de Souza Lima Filho, Irochima Pinheiro, and Oréfice have exclusive rights to intellectual property of this invention secured by a patent application filed with the Instituto Nacional da Propriedade Industrial.

Toward improving therapeutic regimens for Bacillus endophthalmitis

PURPOSE

Bacillus cereus causes the most virulent and refractory form of endophthalmitis. The authors analyzed the effectiveness of early treatment with vancomycin or gatifloxacin, with or without dexamethasone, for experimental B. cereus endophthalmitis.

METHODS

Rabbit eyes were injected intravitreally with 100 colony-forming units of B. cereus. At 2, 4, or 6 hours after infection, eyes were injected intravitreally with 0.1 mL gatifloxacin (0.3%), vancomycin (1.0%), either antibiotic plus dexamethasone, dexamethasone alone (1.0%), or PBS. Eyes were analyzed by electroretinography, bacterial quantitation, and antibiotic penetration analysis. Drug toxicity toward Müller cells, retinal pigment epithelium, and cones was also analyzed.

RESULTS

Eyes treated at 2 hours with vancomycin or gatifloxacin, with or without dexamethasone, maintained higher ERG amplitudes than the dexamethasone alone and PBS control groups. Eyes treated with antibiotic plus dexamethasone at 6 hours had reduced retinal function compared to antibiotic treatment alone. With the exception of vancomycin with or without dexamethasone at 6 hours, all antibiotic treatments sterilized eyes. Only gatifloxacin reached aqueous concentrations greater than the minimal inhibitory concentration for B. cereus when measured at 8 hours. Neither gatifloxacin nor vancomycin was toxic to retinal cells in vitro.

CONCLUSIONS

Early intravitreal injection of vancomycin or gatifloxacin improved the therapeutic outcome of B. cereus endophthalmitis. The addition of dexamethasone to antibiotic treatment did not provide a therapeutic benefit over antibiotics alone and appeared to reduce the antibiotic efficacy of vancomycin 6 hours after infection. In this model, delay in treatment past 6 hours significantly reduced the potential for salvaging useful vision.

Current methodologies for the analysis of aminoglycosides

The aminoglycosides are a large and diverse class of antibiotics that characteristically contain two or more aminosugars linked by glycosidic bonds to an aminocyclitol component. Structures are presented for over 30 of the most important members of this family of compounds. The use of aminoglycosides in clinical and veterinary medicine and in agriculture is described. Qualitative methods for aminoglycoside analysis include X-ray crystallography, nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS). The major part of this article comprises a comprehensive review of quantitative methods for the determination of aminoglycosides. These are microbiological assay, radiochemical assay, radioimmunoassay, enzyme immunoassay, fluoroimmunoassay and other immunoassays, spectrophotometric and other non-separative methods, gas chromatography (GC), thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), and capillary electrophoresis (CE). Simple spectrophotometric methods may be adequate for the assay of bulk pharmaceuticals and their formulations. Microbiological assays make useful semi-quantitative screening tests for the analysis of veterinary drug residues in food, but rapid enzyme immunoassays are more suitable for accurate measurements of aminoglycosides in complex matrices. Automated immunoassays are the most appropriate methods for serum aminoglycoside determinations during therapeutic drug monitoring. HPLC techniques provide the specificity and sensitivity required for pharmacokinetic and other research studies, while HPLC-MS is employed for the confirmation of veterinary drug residues. The potential for further development of chromatographic and CE methods for the analysis of biological samples is outlined.

Effectiveness of specific antibiotic/steroid combinations for therapy of experimental Pseudomonas aeruginosa keratitis

Ciprofloxacin and prednisolone, but not an aminoglycoside and dexamethasone, were previously found to be effective in killing bacteria and reducing inflammation for the treatment of Pseudomonas keratitis. We investigated the therapeutic effectiveness of tobramycin/prednisolone and ciprofloxacin/dexamethasone in a rabbit model of experimental keratitis to increase our understanding of the effectiveness of antibiotic/steroid combinations. To our knowledge, this is the first analysis of the effectiveness of a combination of ciprofloxacin and dexamethasone for experimental keratitis. Two experiments were conducted. In the first experiment, 36 rabbits were divided into six groups: 1) untreated; 2) prednisolone acetate, 1.0%; 3) prednisolone phosphate, 1.0%; 4) tobramycin, 1.36%; 5) tobramycin plus prednisolone acetate; 6) tobramycin plus prednisolone phosphate. In the second experiment, 23 rabbits were divided into four groups: 1) untreated; 2) ciprofloxacin, 0.3%, plus dexamethasone alcohol, 0.1%; 3) ciprofloxacin; 4) dexamethasone alcohol. Topical antibiotic and/or steroid was given for 10 h, from 16 to 26 h postinfection, one drop every 15 min for the first hour and then every 30 min for the remaining 9 h. At 27 h postinfection, eyes were evaluated by slit lamp examination (SLE) and assayed for the presence of bacteria in terms of colony forming units (CFU) per cornea. Both prednisolone acetate and prednisolone phosphate reduced ocular inflammation (as determined by SLE), compared with no treatment (P < or = 0.036); the phosphate was more effective (P = 0.005). Tobramycin alone and in combination with prednisolone also significantly reduced SLE, compared with no treatment (P < or = 0.006). The bactericidal activity of tobramycin was not affected by either steroid formulation.(ABSTRACT TRUNCATED AT 250 WORDS)