Atsutoshi Ota

Cyclosporine A Formulation Affects Its Ocular Distribution in Rabbits

Systemic Cyclosporine A (CsA) administration averts graft rejection after organ transplantation. In the eye, CsA is also beneficial in the treatment of autoimmune diseases, uveitis, Bechet’s disease, Sjögren’s syndrome, keratoconjunctivis sicca, and corneal transplantation (1). It has been suggested that topical rather than systemic CsA application could also be therapeutic, without causing systemic side effects, in the treatment of ocular disease. This may be possible because much less CsA can penetrate into the bloodstream after its topical instillation in either an aqueousor oil-based medium. It is expected that penetration from an aqueous medium will be even less than in oil because its solubility in water is much less. Various attempts were made to develop ophthalmic formulations that improve ocular CsA penetration, including an alpha-cyclodextrin vehicle (2), vegetable oils (3), liposomes (4), collagen shields (5), microor nanospheres (6), and oilin-water emulsion (7). However, none of these deliver therapeutic amounts of CsA into target ocular tissues with low ocular toxicity. In this work, we compared in rabbit ocular tissues CsA pharmacokinetics and distribution resulting from its topical application as an oil-based medium, o/w emulsion, and CsA aqueous clear solution containing a surfactant. Our results suggest that only an aqueous solution containing the nonionic surfactant MYS-40 delivers therapeutic levels of CsA.

Resolution of the enantiomers of thiol compounds by reversed-phase liquid chromatography using chiral derivatization with 2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl isothiocyanate

Abstract A new derivatization procedure has been developed for converting enantiomeric thiol compounds into their diastereomers for resolution by reversed-phase liquid chromatography. The thiol compounds were derivatized with 2,3,4,6-tetra-O-acetyl-β- d -glucopyranosyl isothiocyanate as chiral derivatization reagent and triethylamine as basic catalyst. The thiol group reacted smoothly with the isothiocyanate to form the dithiocarbamate derivative within 30 min at room temperature. The reaction mixture can be injected directly into the chromatograph without purification procedures. The ultraviolet detection wavelength was set at 250 nm, based on the absorption of the thiocarbonyl group. The resulting diastereomers were well separated on an octadecyl-bonded silica column with methanol-0.01 M phosphate buffer as the mobile phase.

Characterization of the carrier-mediated transport of levofloxacin, a fluoroquinolone antimicrobial agent, in rabbit cornea.

The cornea presents a formidable barrier to drug penetration. The fluoroquinolone levofloxacin, which is an effective antimicrobial agent, has the potential to be used in the topical treatment of ocular disease. Thus, we sought to characterize how levofloxacin penetrates the cornea. To perform this characterization, we measured the time dependent permeation of levofloxacin across the isolated rabbit cornea using a diffusion chamber, and compared it with antipyrine fluxes.

Cultured rabbit corneal epithelium elicits levofloxacin absorption and secretion.

Evidence for carrier‐mediated transport of levofloxacin in the isolated rabbit cornea has been found. However, it is not known whether this mechanism is located in the epithelium or the endothelium. To resolve this question, we have measured the kinetics of levofloxacin uptake in primary cultures of rabbit corneal epithelial cells.

Direct high-performance liquid chromatographic resolution of a novel benzothiazine Ca2+ antagonist and related compounds

Abstract Enantiomers of 3,4-dihydro-2-{;5-methoxy-2-[3-(N-methyl-N-{;2-[(3,4-methylenedioxy)phenoxy]ethyl};amino)propoxy]phneyl};-4-methyl-3-oxo-2H-1,4- benzothiazine hydorgen fumarate (I), a novel and potent Ca 2+ antagonist, and its synthetic pecursors, phenol (II) and bromide (III), were directly resolved by high-performance liquid chromatography on a chiral column, with a stationary phase of cellulose carbamate-coated silica gel. Further, the resolution of some 2-(substituted-phenyl)benzothiazines (IVa–IVl) was investigated to study the effects of 2-phenyl ring substituents on chial recognition. As an index of the characteristics of substituents, substituent constants for quantitative structure-activity relationship studies were used. The correlations between the resolution efficiency ( R s ) and the substituent constants for these benzothiazines were investigated by regression analysis. As a result, for 2-(4-substituted-phenyl)-benzothiazines, R s showed good correlation with E s , Tafts steric parameter [correlation coefficient ( r ) = 0.99]. It was also shown that R s correlated with R , an electronic constant for the resonance effect, for 2-(2-hydroxy-5-substituted-phenyl)benzothiazines ( r =0.92). These findings suggest that the 2-phenyl ring plays an important role in chiral recognition in the resolution of these benzothiazines.

Pharmaceutical design of Kary Uni® ophthalmic suspension

Pirenoxine ophthalmic solution was developed based on the quinoid theory which is one of the theories for development mechanism of senile cataracts, and its usefulness for treatment of cataracts has been proved. Since pirenoxine is unstable in aqueous solution, conventional products are required the reconstitution procedure of tablet (or granule) with accompanied solvent before use. Therefore, there are some problems with respect to good patients compliance. Under these circumstances, one bottle type and stable pirenoxine ophthalmic product has been desired. Our concepts for designing new pirenoxine ophthalmic product are as follows, (1) To be one bottle type product, (2) To stabilize pirenoxine in aqueous media for three years at room temperature, (3) To keep its bioequivalence to conventional products. Pirenoxine showed very low solubility in acidic aqueous solution and good stability in aqueous suspension (pH 3.4-4.0) for three years at room temperature in our study. On the other hand, pirenoxine showed good solubility in neutral aqueous solution. We applied these unique properties and developed a new pirenoxine ophthalmic product, Kary Uni® ophthalmic suspension. As no buffer agent is contained in Kary Uni® ophthalmic suspension, the pH of the solution is elevated to the physicological pH of tears immediately after instillation, and pirenoxine microparticles rapidly dissolve in tears. As a result, the bioequivalence to conventional products can be obtained. Kary Uni® is a one bottle type ophthalmic suspension in ready to use, without the reconstitution procedure required for conventional products and is especially evaluated as a new type DDS pharmaceutical product taking advantage of the transformation on the living environment of ocular surface.