Gentamicin in ophthalmology

Niosome-encapsulated gentamicin for ophthalmic controlled delivery

The objective of the present research was to investigate the feasibility of using non-ionic surfactant vesicles (niosomes) as carriers for the ophthalmic controlled delivery of a water soluble local antibiotic; gentamicin sulphate. Niosomal formulations were prepared using various surfactants (Tween 60, Tween 80 or Brij 35), in the presence of cholesterol and a negative charge inducer dicetyl phosphate (DCP) in different molar ratios and by employing a thin film hydration technique. The ability of these vesicles to entrap the studied drug was evaluated by determining the entrapment efficiency %EE after centrifugation and separation of the formed vesicles. Photomicroscopy and transmission electron microscopy as well as particle size analysis were used to study the formation, morphology and size of the drug loaded niosomes. Results showed a substantial change in the release rate and an alteration in the %EE of gentamicin sulphate from niosomal formulations upon varying type of surfactant, cholesterol content and presence or absence of DCP. In-vitro drug release results confirmed that niosomal formulations have exhibited a high retention of gentamicin sulphate inside the vesicles such that their in vitro release was slower compared to the drug solution. A preparation with 1:1:0.1 molar ratio of Tween 60, cholesterol and DCP gave the most advantageous entrapment (92.02% +/- 1.43) and release results (Q(8h) = 66.29% +/- 1.33) as compared to other compositions. Ocular irritancy test performed on albino rabbits, showed no sign of irritation for all tested niosomal formulations.

In vitro toxicity of netilmicin and ofloxacin on corneal epithelial cells

PURPOSE

To evaluate the in vitro cytotoxic effect of the aminoglycoside antibiotic netilmicin on rabbit corneal epithelial cells (SIRC) compared with ofloxacin, a commonly used fluoroquinolone ocular antibiotic.

METHODS

SIRC cell cultures were incubated for 8 to 72 h in the presence and absence of netilmicin (1.5, 3, and 6 mg/mL) and equal concentrations of ofloxacin. Cell viability in treated and untreated SIRC cells was measured by both neutral red and MTT colorimetric assays at 8, 24, and 72 h, whereas changes in cell morphology were examined at 8, 24, 48, and 72 hours by the use of phase-contrast microscopy.

RESULTS

Netilmicin, at all tested concentrations, failed to alter SIRC cell viability or morphology. In contrast, all concentrations of ofloxacin caused statistically significant dose- and time-dependent reductions in cell viability even after 8 h. After 72 h there was complete loss of cell viability. Morphologic examination of SIRC cells after 8 h of incubation with ofloxacin revealed that the fluoroquinolone antibiotic, at all concentrations, produced large numbers of dead cells, compromised intercellular contacts, and altered general morphology. After 48 h the cell monolayer was observed to be completely destroyed.

CONCLUSION

Netilmicin, at the concentrations used, is an antibiotic devoid of obvious cellular toxicity and may also be considered as a suitable first-choice drug in the treatment of those pathologies that compromise the integrity of the ocular surface.

A new method for continuous intraocular drug delivery

A novel device for the continuous intraocular delivery of drugs is described. The active intraocular component of the device is made from hollow haemodialysis fibres. During operation, the drug to be administered diffuses from a small extraocular reservoir to the intraocular fibres, where it passes through the semipermeable walls and into the vitreous body. The delivery of gentamicin by the device into the vitreous body of the cat is compared with direct intraocular injection techniques. Characteristics of the process of drug delivery were influenced by the geometry and design of the device. A reservoir concentration of 10 g/L gentamicin sulphate in a device with four fibres, each 5 mm long, resulted in stable vitreal gentamicin levels of 104 to 128 mg/L at 10 hours. Intravitreal injection of 0.1 ml of a 10 g/L solution of gentamicin caused localised peaks of intravitreal gentamicin concentration in the range 1180 to 3296 mg/L, before falling to 356 to 665 mg/L at 10 hours. The device provides the opportunity of a more controlled and continuous drug delivery, thus avoiding the high localised concentrations that may occur with direct injection techniques in which the required dose is delivered as a bolus. Refinement of a device of this type may result in a clinically useful method of intraocular drug delivery for drugs which present a risk of localised retinal toxicity or require repetitive administration with conventional intraocular injection techniques.

Effects of gentamicin on healing of transdifferentiating conjunctival epithelium in rabbit eyes

We examined the effects of commercially prepared gentamicin, a wide-spectrum topical antibiotic, on the healing of epithelial defects of the rabbit cornea. Abrasions were created by: (1) removing the corneal epithelium and 3 mm of the conjunctival epithelium (Group 1); and (2) producing the same initial trauma and subsequently removing the central 8 mm of epithelium 28 days after initial healing (Group 2). The complete healing of the large corneal and conjunctival epithelial defects was not delayed when gentamicin solution was used four times a day (Group 1). When the healed epithelium was reinjured while transdifferentiating from conjunctival to corneal epithelium (day 28, Group 2), treatment with the gentamicin solution and its vehicle, both containing benzalkonium chloride, delayed epithelial healing significantly compared with treatment with saline (P less than .01).

Corneal cytotoxicity of topically applied drugs, vehicles and preservatives

The toxicity and side effects of drugs and their adjuncts are reviewed according to effect on corneal epithelium, stroma, and endothelium, when topically applied to healthy or wounded surfaces, or introduced into the anterior chamber of the eye. Corneal research techniques are reviewed, including scanning and transmission electron microscopy, electrophysiological techniques, and specular microscope observation. Clinical interpretation of these results is discussed. Reviews of specific toxicologic techniques and of medications are cited. Present research makes it increasingly apparent that not only medications but also their preservatives cannot be considered innocuous. Preservatives may be effective yet less damaging to the ocular integument when used at lower concentrations than those presently available commercially. Complete avoidance of preservatives by the use of special dispensing systems is found increasingly desirable.