Fabrication of a drug delivery system that enhances antifungal drug corneal penetration

Abstract

Fungal keratitis (FK) remains a severe eye disease, and effective therapies are limited by drug shortages and critical ocular barriers. Despite the high antifungal potency and broad spectrum of econazole, its strong irritant and insolubility in water hinder its ocular application. We designed and fabricated a new drug delivery system based on a polymeric vector for the ocular antifungal application of econazole. This novel system integrates the advantages of its constituent units and exhibits superior comprehensive performance. Using the new system, drug content was significantly increased more than 600 folds. The results of in vivo and in vitro experiments demonstrated that the econazole-loaded formulation exhibited significantly enhanced corneal penetration after a single topical ocular administration, excellent antifungal activity, and good tolerance in rabbits. Drug concentrations and ocular relative bioavailability in the cornea were 59- and 29-time greater than those in the control group, respectively. Following the topical administration of one eye drop (50 μL of 0.3% w/v econazole) in fungus-infected rabbits, a high concentration of antimycotic drugs in the cornea and aqueous humor was sustained and effective for 4 h. The mechanism of corneal penetration was also explored using dual fluorescent labeling. This novel drug delivery system is a promising therapeutic approach for oculomycosis and could serve as a candidate strategy for use with various hydrophobic drugs to overcome barriers in the treatment of many other ocular diseases.

Keywords: Fungal keratitis; corneal penetration; dual fluorescent label; pharmacokinetics; polymeric vector.

Figure 1.

(A) Two major barriers to topical ocular drug delivery. Tear film barrier: a high tear turnover rate and gel-like mucus layer. Corneal barrier: tight junctions in the corneal epithelial cells and alternating polarity five-layer structure. (B) Schematic illustration of vector synthesis, drug loading, and the virtues of NDDS for ocular topical administration.

Figure 2.

Representative pictures of the in vivo rabbit ocular irritation test; the experience group received econazole (ECZ)-loaded NDDS eye drops, the control group received saline (control group), and the suspension group received ECZ nitrate suspension.

Figure 3.

Pharmacokinetics studies in rabbit eyes after a single instillation of either formulation. Econazole (ECZ) concentration time profiles in (A) cornea and (B) aqueous humor of rabbits. The drugs included 0.3% of ECZ solution eye drops (E group) and 0.3% of ECZ suspension eye drops (C group) with a single dose of 50 µL. Values are given as the mean ± SD (n = 6), ND, not detected; DCE, debrided corneal epithelium; and ICE, intact corneal epithelium. ∗p < .05 for E group with DCE versus with ICE; ∗∗p < .01 for E group with DCE vs. C group with DCE and E group with ICE (unpaired t-test).

Figure 4.

Representative in vivo two-photon microscopy corneal cross-section images at different times after topical administration of the dual fluorescently labeled formulation of Cy5 and C6 in c57Bl/6 mice. The tests were performed under (A) ICE and (B) DCE (magnification, 100×).

Figure 5.

Schematic illustration of the corneal penetration behavior of NDDSs after topical administration under ICE and DCE in vivo.

Figure 6.

In vitro drug sensitivity of fungi using different methods. (A) Disc diffusion method. Experience group, econazole (ECZ) loading in NDDS; negative control, ECZ suspension; positive control, natamycin eye drops. (B) Microdilution method. E group, ECZ solution eye drops; C group for E, ECZ suspension eye drops; and C group for V, voriconazole solution eye drops. The curves represent the inhibition of fungal spores by ECZ and voriconazole.