Ultrasound-enhanced delivery of antibiotics and anti-inflammatory drugs into the eye

Abstract

Delivery of sufficient amounts of therapeutic drugs into the eye is often a challenging task. In this study, ultrasound application (frequencies of 400 KHz to 1 MHz, intensities of 0.3-1.0 W/cm(2) and exposure duration of 5 min) was investigated to overcome the barrier properties of cornea, which is a typical route for topical administration of ophthalmic drugs. Permeability of ophthalmic drugs, tobramycin and dexamethasone and sodium fluorescein, a drug-mimicking compound, was studied in ultrasound- and sham-treated rabbit corneas in vitro using a standard diffusion cell setup. Light microscopy observations were used to determine ultrasound-induced structural changes in the cornea. For tobramycin, an increase in permeability for ultrasound- and sham-treated corneas was not statistically significant. Increase of 46%-126% and 32%-109% in corneal permeability was observed for sodium fluorescein and dexamethasone, respectively, with statistical significance (p < 0.05) achieved at all treatment parameter combinations (compared with sham treatments) except for 1-MHz ultrasound applications for dexamethasone experiments. This permeability increase was highest at 400 kHz and appeared to be higher at higher intensities applied. Histologic analysis showed structural changes that were limited to epithelial layers of cornea. In summary, ultrasound application provided enhancement of drug delivery, increasing the permeability of the cornea for the anti-inflammatory ocular drug dexamethasone. Future investigations are needed to determine the effectiveness and safety of this application in in vivo long-term survival studies.

Fig. 1

Diffusion cell setup. The dissected cornea was placed between donor and receiver compartments, with the epithelial layer facing the donor compartment. The receiver compartment was filled with DPBS, and the donor compartment was filled with a drug solution. The transducer was positioned at different distances from the cornea (at d_ff) based on the frequency of the transducer. Ultrasound was applied for 5 min, and the cornea was exposed to drug solution for 60 min.

Fig. 2

Histologic observations. Examples from semi-quantitative analysis study of histologic slides for investigation of corneal damage. (a) Class 0: sham-treated cornea. The surface epithelial cells appear intact (arrow). (b) Class 1: ultrasound application at 1 MHz and 1 W/cm². Minor structural changes are present in the surface of the epithelium (arrow), with some cells missing. (c) Class 2: ultrasound application at 400 KHz and 1 W/cm². Cells in two layers of epithelium are damaged, missing, or both. (d) Class 3: ultrasound application at 600 KHz and 1 W/cm². Severe epithelial damage is observed.

Fig. 3

The effects of ultrasound on the corneal permeability in the case of sodium fluorescein. Control (sham treatment) represents the corneal permeability with no ultrasound treatment, compared with the corneal permeability at 400 KHz to 1 MHz and 1 W/cm² with ultrasound exposure of 5 min. The mean and standard deviation are shown from 9 to 13 experiments per condition. The permeability of ultrasound-treated corneas was up by 126% compared with sham-treated corneas (p < 0.05). *p < 0.05; **p < 0.001.

Fig. 4

The effects of ultrasound on the corneal permeability in the case of tobramycin. Control (sham treatment) represents the corneal permeability with no ultrasound treatment; different shades of gray represent the corneal permeability at intensities of 0.5–1.0 W/cm² and frequencies of 400 KHz to 1 MHz, and ultrasound exposure of 5 min. Number of experiments per experimental condition was 9–18. Data are given as mean ± standard deviation. No statistically significant permeability increase was detected for this drug.

Fig. 5

The effects of ultrasound on the corneal permeability in the case of dexamethasone. Control (sham treatment) represents the corneal permeability with no ultrasound treatment; different shades of gray represent the corneal permeability at intensities of 0.3–1.0 W/cm² and frequencies of 400 KHz to 1 MHz and ultrasound exposure of 5 min. The number of experiments per experimental condition was five to nine. Data are given as mean ± standard deviation. Statistically significant (p < 0.05) permeability increase was observed at all tested parameters, except for ultrasound application at 1 MHz. *p < 0.05; **p < 0.001.

Fig. 6

Corneal changes resulting from ultrasound application compared with control (sham-treated) corneas. Control shows the corneal changes with no ultrasound treatment; different shades of gray represents the corneal damage resulting from ultrasound application (intensities of 0.5–1.0 W/cm², frequencies of 400 KHz to 1 MHz, exposure duration of 5 min). Data are shown as mean ± standard deviation (n = 6–33). *p < 0.05; **p < 0.01; ***p < 0.001.