Pharmacokinetic features of difluprednate ophthalmic emulsion in rabbits as determined by glucocorticoid receptor-binding bioassay.

PURPOSE: Difluprednate (6α,9-difluoro-11ß,17,21-trihydroxy-1,4-pregnadiene-3,20-dione 21-acetate 17-butyrate, DFBA) has long been used as an anti-inflammatory dermatological agent. The main objectives of the current study were to evaluate the pharmacokinetic and pharmacodynamic features of DFBA when used as an ophthalmic agent, and to compare these features with those of other common ophthalmic agents, to determine which has the highest activity. METHODS: A glucocorticoid (GC) receptor-binding test was performed to evaluate GC receptor-binding activity (GCRBA, the index of pharmacological effect). Using this information, we calculated dose-response curves, IC(50) values, and K(d) values to evaluate each drug's K(i) value. Finally, we performed studies in live rabbits to compare the activity of 4 formulations [0.002%, 0.01%, or 0.05% DFBA, or an ophthalmic solution of 0.1% betamethasone sodium phosphate (BMP)] at 4 time points (0.5, 1, 2, 4 h). At each time point, blood and eye samples were taken so that C(max) (the maximum equivalent concentration of the active DFBA metabolite, DFB), T(max) (the time at which C(max) was measured), and the area under the concentration-time curve could be compared across the 4 formulations. RESULTS: BMP had the highest K(i) value (8.4 × 10(-8) nmol/L), whereas DFB had the lowest (6.1 × 10(-11) nmol/L). The GCRBA of DFBA was intermediate to these 2 values (7.8 × 10(-10) nmol/L). Instillation of the DFBA ophthalmic emulsion in the eyes of rabbits led to dose-dependent increases in GCRBA, which was mostly attributable to the activity of DFB. The 0.05% DFBA ophthalmic emulsion elicited the greatest response in both aqueous humor and iris/ciliary body tissues, though there were no significant dose-dependent differences in GCRBA in plasma samples. CONCLUSIONS: The 0.05% DFBA ophthalmic emulsion appears to be an effective and safe anti-inflammatory treatment in ocular tissues. It is comparable, and possibly even superior, to the 0.1% BMP solution, and may be particularly useful in cases of severe disease where treatment with BMP solution alone is insufficient.

Ocular distribution of difluprednate ophthalmic emulsion 0.05% in rabbits.

PURPOSE: To evaluate ocular distribution and excretion of tritium-labeled difluprednate ((3)H-DFBA) ophthalmic emulsion 0.05% after a single or repeated instillation to pigmented rabbit eyes. METHODS: (3)H-DFBA ophthalmic emulsion 0.05% was instilled in the right eyes of pigmented rabbits, in either a single or repeated quater in die (QID) for 3 days or 7 days) dose of 25 µg/50 µL. The radioactivity in right and left ocular tissues, urine, blood, plasma, and feces were measured with a liquid scintillation counter. Additionally, the distribution of radioactivity around ocular tissues was investigated with autoradiography. RESULTS: After a single instillation, the highest maximum radioactive concentrations were found in the cornea (2,081 ng eq./g), followed by the iris/ciliary body (926 ng eq./g), conjunctiva (330 ng eq./g), anterior retina/choroid (273 ng eq./g), sclera (222 ng eq./g), and aqueous humor (144 ng eq./mL) of treated eyes. The maximum radioactivity concentration of the posterior retina/choroid was 59 ng eq./g, and difluprednate delivered as a topical ophthalmic emulsion reached the back of the eye. However, radioactivity in untreated eyes was very low. Total radioactivity excreted in urine and feces 168 h after a single instillation was 99.5% of the total dose. Radioactivity concentration levels measured 24 h after 28 instillations were no more than twice those measured 24 h after 12 instillations. Radioactive concentrations in ocular and periocular tissues were highest at 0.5 or 1 h after a single instillation, and were mostly eliminated from these tissues by the end of the study. Radioactivity was barely detectable in the blood, with very little accumulation even after multiple doses. CONCLUSIONS: After instillation of (3)H-DFBA ophthalmic emulsion 0.05% in rabbit eyes, radioactivity was distributed at the anterior segment and cleared rapidly. Some radioactivity was detected in the posterior retina/choroid, suggesting that difluprednate and its metabolites reach these tissues. These results suggest that difluprednate delivered as a topical ophthalmic emulsion reached the anterior and posterior segments of the eye quickly and may be a potential treatment for ocular inflammation in these areas.

Metabolic profiles of difluprednate in rabbit ocular tissues after instillation of difluprednate ophthalmic emulsion.

Difluprednate (DFBA; 6alpha,9-difluoro-11beta,17,21-trihydroxy-1,4-pregnadiene-3,20-dione 21-acetate 17-butyrate) is an effective anti-inflammatory agent derived from prednisolone. The present study aimed to evaluate the metabolite profile of DFBA in rabbit ocular tissues after instillation of DFBA ophthalmic emulsion. The high-performance liquid chromatography with radiochemical detection was employed to analyze radioactivity in rabbit ocular tissues that had been instilled with a (3)H-DFBA 0.05% ophthalmic emulsion. At 0.5 and 2 h after instillation, DFBA was not detected in the cornea, aqueous humor, or iris/ciliary body. Instead, 21-deacetylated DFBA (DFB), 17-debutylated DFB (DF), and an unknown metabolite were found. The unknown metabolite was identified as de-17-side chain-glucocorticoid metabolite (DF21C), which is a novel glucocorticoid metabolite formed by the scission of the 17-side chain via an unknown metabolic reaction pathway. The K(i) value of DF21C was 5.6 x 10(-7) mol/L, indicating very weak glucocorticoid receptor binding of DF21C (approximately 1000-fold less than that of DFBA and DFB).

Effect of dosing interval on the efficacy of topical ophthalmic gatifloxacin against Enterococcus faecalis in an in vitro pharmacokinetic model simulating the local eye compartment.

Improved dosing regimens have been proposed for various antimicrobial agents by application of pharmacokinetic/pharmacodynamic (PK/PD) principles. However, for topical ophthalmic use there are several limitations to changing the dosing regimen, such as drug formulation and bioavailability. In this study, we investigated the relationship between dosing interval and antibacterial efficacy in an in vitro PK model mimicking post-operative endophthalmitis. The in vitro PK model simulated the aqueous humour concentration following topical application of 0.3% gatifloxacin ophthalmic solution to rabbit eyes. A clinical isolate of Enterococcus faecalis was exposed to gatifloxacin three times repeatedly at various intervals from 0 h to 8 h. The area between the control growth curve and the bacterial killing and re-growth curve for 24 h (ABBC) was used to evaluate efficacy. The ABBC showed bell-shaped dependence on the dosing interval with a peak at 3h. Under limited condition of total exposure amount, i.e. area under the concentration-time curve, the antimicrobial efficacy appears to be associated with the cumulative time of a 24-h period such that the concentration exceeds the minimum inhibitory concentration (T>MIC) rather than the peak concentration:MIC ratio. The length of intermission of T>MIC during repeated dosing appears to be proportional to the decrease in efficacy of gatifloxacin against E. faecalis. A longer dosing interval, as long as T>MIC is continuous, would likely be more efficient at preventing post-operative enterococcal endophthalmitis. However, further investigation is necessary to explore whether this model is applicable to a variety of pathogens and drugs.

Ocular pharmacokinetics of a single dose of bromfenac sodium ophthalmic solution 0.1% in human aqueous humor.

PURPOSE: The aim of this study was to evaluate the ocular pharmacokinetics of a single dose of bromfenac sodium ophthalmic solution 0.1% in subjects undergoing routine cataract surgery with intraocular lens implantation. METHODS: An open-label, phase II confirmatory study of 54 subjects undergoing cataract surgery with intraocular lens implantation. A single drop of bromfenac sodium ophthalmic solution 0.1% was administered at 30, 60, 90, 120, 180, or 240 min prior to the initiation of cataract surgery. Samples of aqueous humor were aspirated through a paracentesis and analyzed by using high-performance liquid chromatography. Based upon these data, predicted concentrations of bromfenac in the aqueous humor over 24 h were generated by using computer simulation and compared with the IC(50) for bromfenac as a measure of anti-inflammatory efficacy. RESULTS: Peak aqueous-humor concentrations of bromfenac occurred between 150 and 180 min following ophthalmic dosing, with a mean concentration of 78.7 ng/mL. The level of bromfenac decreased in a log-linear fashion with an elimination-rate constant of 1.4. Bromfenac remained above the IC(50) value of cyclo-oxygenase-2 (COX-2) during the evaluated time points and over the 12-h dosing interval, using a computer model of extrapolated time points and assuming first-order elimination. CONCLUSIONS: Pharmacokinetic modeling, based upon samples collected over 240 min after a single dose of bromfenac sodium ophthalmic solution 0.1% suggests that aqueous-humor concentrations remain at clinically effective levels (above its IC(50) value for COX-2) for over 12 h. Based upon this rationale, these results supported clinical trials that demonstrated the efficacy of twice-daily dosing of bromfenac sodium ophthalmic solution 0.1% to manage patients with postoperative ocular pain and inflammation.

Prophylactic efficacy of ophthalmic quinolones in experimental endophthalmitis in rabbits.

PURPOSE: The aim of this study was to determine the efficacy of 0.3% gatifloxacin ophthalmic solution in preventing bacterial endophthalmitis in rabbits. METHODS: Eighty-four (84) albino phakic rabbits were injected unilaterally with 2 x 10(4) colony forming units of Enterococcus faecalis into the anterior chamber. The eyes received 0.3% ofloxacin ophthalmic ointment or 0.3% gatifloxacin ophthalmic solution with different regimens in three separate experiments: (1) 1 or 3 drops of gatifloxacin every 2 h or a single application of ofloxacin for 1 day; (2) 3 drops/day of gatifloxacin application started at 0, 6, and 24 h postinoculation, or 1 drop at 0 h, and 3 times daily gatifloxacin for the following 3 days; and (3) 1 or 3 drops of gatifloxacin application started at 0 h and no further application for the following 3 days. The control eyes received no treatment in the three experiments. The effectiveness of these different regimens was assessed by slit-lamp biomicroscopy and bacterial colony counts. The ocular penetration of the drugs was determined in a separate experiment, using 36 normal albino rabbits. RESULTS: The concentration-time curves for gatifloxacin and ofloxacin appeared parallel, with mean peak concentrations of 1161 and 219 ng/mL, respectively, at 1 h postinstillation. In Experiment 1, gatifloxacin significantly reduced the inflammation and the number of living bacteria in the aqueous humor, compared with controls, whereas ofloxacin ointment did not. A single application of ofloxacin ointment was not better than 1 drop of gatifloxacin. The results of Experiment 2 showed that the effectiveness of gatifloxacin decreased as the interval between the inoculation and the onset of treatment increased. In Experiment 3, only 3 drops of gatifloxacin on day 1 kept the inflammation significantly lower than that in the control for 4 days. CONCLUSIONS: Immediate postoperative prophylaxis would likely be effective in reducing the risk of enterococcal endophthalmitis by topical gatifloxacin.

Improvement of the ocular bioavailability of carteolol by ion pair.

Ocular bioavailability after instillation of carteolol was investigated by ion pair formation, taking into consideration a balance between lipophilicity and water solubility. The octanol/ water partition coefficient (PC(O/W)) and the aqueous humor concentration in rabbits after instillation of carteolol containing fatty acids having not more than 6 carbons were measured. The longer carbon chain fatty acid showed the higher PC(O/W) of carteolol. The aqueous humor concentration of carteolol increased with carbon chain length of fatty acid and was clearly correlated with logPC(O/W). The increment of counter ion also increased both the logPC(O/W) and aqueous humor concentration of carteolol. The findings suggested that the transcorneal absorption of carteolol would be designed by coordinating with quality and quantity of counter ions. The area under concentration (AUC) in aqueous humor applied by ion pair formulation containing 2% carteolol with sorbate was 2.6 times higher than that by 2% carteolol ophthalmic solution (control), whereas the AUC applied by 4% carteolol ophthalmic solution was 1.4 times higher. The plasma level after instillation of ion pair formulation was almost the same as that of 2% ophthalmic solution. The ratio of AUC (aqueous humor/ plasma) of ion pair formulation was markedly higher, as compared with those of 2% and 4% ophthalmic solution. These results showed that the ion pair formation with sorbate improved the ocular bioavailability of carteolol without enhancing systemic absorption.