A Kinetic Approach to Determining Drug Distribution in Complex Biphasic Systems.

Pharmaceutical emulsions contain multiple components, such as micellar, aqueous, and oil phases, leading to complex drug transfer and equilibrium phenomena. These complex components present challenges for the bioequivalence assessment of the drug products. The objective of the study was to develop a method that can probe the underlying mechanism and process of drug distribution. The concept of drug partitioning into biphasic systems was used to simplify the complex transfer phenomenon. A kinetic method was developed taking into account the biphasic diffusion. Using this approach, both the rate (kinetics) and the extent (equilibrium) of distribution can be determined. For method development purpose, 3 model compounds (triamcinolone acetonide, difluprednate, and cyclosporine), with expected partition coefficient values ranging from 2 to 6, were tested using the kinetic method and the traditional shake-flask method. The values obtained by the 2 methods for all compounds correlated well (r2 = 0.825). Various organic and aqueous solvents which are commonly encountered in formulations were also tested to determine the impact of phase composition on drug distribution. The kinetic method was found to offer more flexibility in terms of solvent composition and can lead to better understanding for drug distribution and potential drug release in complex biphasic systems.

Disposition of isoflupredone acetate in plasma, urine and synovial fluid following intra-articular administration to exercised Thoroughbred horses.

The use of isoflupredone acetate in performance horses and the scarcity of published pharmacokinetic data necessitate further study. The objective of the current study was to describe the plasma pharmacokinetics of isoflupredone acetate as well as time-related urine and synovial fluid concentrations following intra-articular administration to horses. Twelve racing-fit adult Thoroughbred horses received a single intra-articular administration (8 mg) of isoflupredone acetate into the right antebrachiocarpal joint. Blood, urine and synovial fluid samples were collected prior to and at various times up to 28 days post drug administration. All samples were analyzed using liquid chromatography-Mass Spectrometry. Plasma data were analyzed using a population pharmacokinetic compartmental model. Maximum measured plasma isoflupredone concentrations were 1.76 ± 0.526 ng/mL at 4.0 ± 1.31 h and 1.63 ± 0.243 ng/mL at 4.75 ± 0.5 h, respectively, for horses that had synovial fluid collected and for those that did not. The plasma beta half-life was 24.2 h. Isoflupredone concentrations were below the limit of detection in all horses by 48 h and 7 days in plasma and urine, respectively. Isoflupredone was detected in the right antebrachiocarpal and middle carpal joints for 8.38 ± 5.21 and 2.38 ± 0.52 days, respectively. Results of this study provide information that can be used to regulate the use of intra-articular isoflupredone in the horse.

Difluprednate for inflammatory eye disorders.

Uveitis is the third leading cause of preventable blindness in the U.S. Topical administration of corticosteroids remains the mainstay in the management of acute autoimmune anterior uveitis. Difluprednate 0.05% ophthalmic emulsion is a potent new topical corticosteroid that exhibits enhanced penetration, better bioavailability, rapid local metabolism and strong efficacy, with a low incidence of adverse effects. In June 2008, difluprednate ophthalmic emulsion 0.05% gained FDA approval in the U.S. for the treatment of postoperative ocular inflammation and pain. Recently, a multicenter, randomized clinical trial showed difluprednate to be noninferior to prednisolone acetate 1% dosed twice as often, the current standard of care for the acute management of endogenous uveitis in the U.S. Furthermore, difluprednate proved to have a comparable safety profile. Here, we review difluprednate pharmacokinetics, ocular indications, animal studies, as well as the results of the clinical trials conducted to date in the U.S.

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).

Formulation of an ophthalmic lipid emulsion containing an anti-inflammatory steroidal drug, difluprednate.

Preparation of oil-in-water (o/w) type lipid emulsion is one of the approaches to formulate drugs that are poorly water-soluble but can be dissolved in the oil phase of the emulsions. A synthetic glucocorticoid medicine, difluprednate (DFBA), is a water-insoluble compound. We formulated DFBA (0.05%, w/v) ophthalmic lipid emulsion containing 5.0% (w/v) caster oil and 4.0% (w/v) polysorbate 80. The appearance of the emulsion was blue and translucent lipid emulsion, and the median particle size of the lipid emulsion was 104.4 nm. Neither separation nor change in particle size was observed after 6 months at 40 degrees C. Furthermore, when compared with DFBA (0.05%, w/v) ophthalmic suspension, the lipid emulsion showed 5.7-fold higher concentration of DFB that was an active metabolite of DFBA in aqueous humor at 1h after instillation. Ophthalmic lipid emulsion enhances the intraocular penetration of drugs, and it is useful as a delivery system for the ophthalmic preparations of lipophilic drugs.

Plasma, urine, and synovial fluid disposition of methylprednisolone acetate and isoflupredone acetate after intra-articular administration in horses.

OBJECTIVE--To document plasma, urine, and synovial fluid disposition of 2 common intra-articularly administered steroid preparations, methylprednisolone acetate (MPA) and isoflupredone acetate (IPA). DESIGN--Descriptive investigation. SAMPLE POPULATION--100 mg of MPA or 4 mg of IPA was administered to 2 groups of 4 healthy sound radiographically normal female horses. PROCEDURE--Blood samples were collected at time 0 (before) and 2, 4, 6, 8, 10, 12, 24, 36, 48, 72, and 96 hours after administration of the designated steroid. Complete urine collection for measurement of designated steroid was accomplished by use of occluding 28-F balloon catheters. Synovial fluid samples were aseptically aspirated from the injected and contralateral uninjected tarsocrural joint at time 0 and 8, 24, 48, 240, and 672 hours after administration of the designated steroid. All samples were screened by ELISA to detect parent drug or metabolite equivalent, with a sensitivity of 2.5 ng/ml for MPA and 0.1 ng/ml for IPA. If drug was detected by ELISA in the plasma or synovial fluid, the samples were further quantified and specified, using HPLC with a lower limit of quantification (10 ng/ml). RESULTS--Between 2 and 12 hours after administration, plasma contained < 10 ng of MPA or IPA/ml (parent drug or metabolite equivalent), as intermittently detected by ELISA. Parent drug or metabolite equivalent was detected in the urine for 24 and 72 hours after injection of IPA and MPA, respectively. Synovial fluid from the contralateral joint contained no detectable MPA or IPA at any sample collection time. Median half-life for MPA, as detected by HPLC, was 10.3 hours (range, 6.1 to 10.6) in the synovial space. Median half-life for methylprednisolone, as detected by HPLC, was 10.4 (range, 9.9 to 32.1) hours. CONCLUSIONS--Both steroids appeared to be rapidly hydrolyzed to their respective ester forms, as detected by HPLC. The ELISA appeared to be a useful screening tool for detection of corticosteroids in this variety of body fluids.