双氯酚酸钠脂质体的制备及其眼部药代动力学

目的研究双氯酚酸钠脂质体的制备方法并考察其在家兔眼部的药代动力学特征。方法采用逆相蒸发法制备双氯酚酸钠正电荷脂质体。脂质体和滴眼液滴眼后家兔采用高效液相色谱法测定角膜前、角膜和房水中药物浓度。结果制得的脂质体平均粒径为226.5 nm，多分散度为0.214，ζ电位为+18.1 mV，经均匀设计优化处方，包封率可达到63%。0.1%双氯酚酸钠脂质体和滴眼液两种制剂家兔局部滴眼后的药代动力学研究显示，脂质体可延缓药物在角膜前的清除，增加角膜中药物的浓度，药物在房水中半衰期延长，以滴眼液为参比制剂，相对生物利用度为211%。结论双氯酚酸钠正电荷脂质体可以增加药物在角膜前的滞留时间，提高角膜渗透性及药物在眼部的生物利用度，减少滴眼次数。     

Pharmacokinetics of the Aldose Reductase Inhibitor Imirestat Following Topical Ocular Administration

The pharmacokinetics of imirestat following topical ocular administration were evaluated in a series of studies in rabbits and dogs. Following single topical doses to both albino and pigmented rabbits, imirestat was subject to rapid uptake into the cornea followed by an initial rapid decline and then very slow elimination, with a t _1/2 of approximately 130 hr. Drug was rapidly absorbed into aqueous humor, with concentrations declining to nondetectable levels by 12 hr. Imirestat was retained in the lens following topical dosing similar to that in cornea, with an apparent elimination t _1/2 of 140 hr. Vitreous humor concentrations of drug were detectable for up to 72 hr after dosing. There was no apparent difference in the disposition of the drug between albino and pigmented rabbits. Bioavailability following topical dosing increased with dose, although not in a linear fashion. Formulation pH did not have an appreciable effect on ocular bioavailability. There was detectable systemic absorption following topical dosing, with plasma concentrations in rabbit being 50 to 75% of that observed following an equivalent intravenous dose. However, drug levels in the dosed eyes were significantly higher than in contralateral undosed eyes. Multiple dosing of imirestat for 6 weeks resulted in accumulation of drug in rabbit lens. Concentrations were higher in lens cortex than lens nucleus, with the time course for accumulation being different for the two. Our data suggest that imirestat penetrates into ocular tissue following topical dosing and is retained in lens and cornea, potential sites of action for the drug.     

Ocular pharmacokinetic/pharmacodynamic modeling for timolol in rabbits using a telemetry system

We have established an ocular pharmacokinetic/pharmacodynamic (PK/PD) model for a beta-adrenergic antagonist, timolol, after instillation into rabbits. Timolol concentrations were determined by HPLC in the tear fluid, aqueous humor, cornea, and iris-ciliary body after instillation or ocular injection into the anterior chamber of the eye in rabbits. In addition, intraocular pressure (IOP) measurement was performed after instillation of timolol by a telemetry system, which was able to obtain detailed IOP data automatically. The PK/PD parameters were estimated by fitting the concentration-time profiles and the ocular hypotensive effect-time profiles using MULTI (RUNGE) program. The PK model consisted of six compartments and the PD model included aqueous humor dynamics based on an action mechanism of timolol, which causes lowering of IOP by suppressing aqueous humor production. The PK/PD model described well the concentration-time profiles and the ocular hypotensive effect-time profiles after instillation of timolol. This study is the first trial to develop an ocular PK/PD model for timolol after instillation. This model can predict both the drug concentrations in various ocular tissues and the ocular hypotensive effect after instillation of timolol.     

Characterization of Ocular Pharmacokinetics of Beta-Blockers Using a Diffusion Model After Instillation

Purpose. To characterize the ocular pharmacokinetics of beta-blockers (timolol and tilisolol) after instillation in the albino rabbit using a mathematical model that includes a diffusion process. Methods. The disposition of fluorescein isothiocyanate-dextran (FITC-dextran, molecular weight 4400), timolol, and tilisolol was determined in tear fluid and aqueous humor after instillation or ocular injection in rabbits. The in vivo penetration parameters were estimated by fitting the concentration-time profiles to the Laplace equations based on a diffusion model using MULTI(FILT) program. Thein vivo permeability of drugs was measured across cornea using a two-chamber diffusion cell. Results. Concentration-time profiles of drugs in the tear fluid after instillation showed a monoexponential curve. Although a monoexponential curve was observed in the aqueous humor concentration of FITC-dextran after injection into the aqueous chamber, timolol and tilisolol showed a biexponential curve. On the basis of these results, anin vivo pharmacokinetic model was developed for estimation of penetration parameters. The in vitro partition parameters were higher than those of the in vivo parameters. Conclusions. The ocular absorption of timolol and tilisolol was characterized using an in vivo pharmacokinetic model and in vivo penetration parameters.     

Disposition of levobunolol after an ophthalmic dose to rabbits

The ocular and systemic disposition of levobunolol (LBUN), an antiglaucoma agent, was studied in albino rabbits. After topical administration to eyes, LBUN was rapidly adsorbed, with 2.5% of the dose bioavailable to the intraocular tissues as intact drug and 46% to the systemic circulation. On passage across the cornea, approximately 4.7% of a topically applied LBUN dose was biotransformed to dihydrolevobunolol (DHB), and subsequently became bioavailable to intraocular tissues. The major sites of ocular metabolism were the cornea epithelium and the iris-ciliary body. Another 12% of the topical LBUN dose entered the systemic circulation as DHB after presystemic biotransformation. Our study indicated a rapid absorption of LBUN into the aqueous humor after topical dosing. The tpeak was 15 min after dosing and the Cmax was 4 micrograms/mL. Dihydrolevobunolol (DHB) was formed steadily and reached a maximum in the aqueous humor 45 min after dosing. After distribution equilibrium had been reached, the aqueous humor concentrations of both LBUN and DHB declined. Six hours after dosing, the concentration of DHB in the aqueous humor was approximately 10 times higher than that of its parent compound. Because DHB is equivalent to its parent compound in beta-blocking activity, its formation in the rabbit eye may contribute to the pharmacodynamic effects observed after topical doses of LBUN.     

Pharmacokinetic prediction of the ocular absorption of an instilled drug with ophthalmic viscous vehicle

We previously developed an in vivo pharmacokinetic model that accounts for the corneal diffusion in albino rabbits and predicts the concentration of beta-blockers in the anterior segments. The purpose of this study is to pharmacokinetically predict the ocular absorption and characterize the systemic absorption of instilled drug with ophthalmic viscous vehicle to assist in its design and evaluation. Tilisolol and carboxymethylcellulose sodium salt (CMC) were used as the model ophthalmic drug and viscous polymer, respectively. After instillation of tilisolol with CMC vehicle in rabbits, the disposition of the drug in tear fluid, aqueous humor, and plasma were determined by HPLC. The ocular and systemic absorption were analyzed by a mathematical model including a diffusion process and a two-compartment model with first-order absorption, respectively. CMC vehicle increased the area under the concentration-time curve (AUC) of tilisolol in the tear fluid and aqueous humor and slightly reduced the AUC in plasma. The concentrations of tilisolol in the aqueous humor after instillation with CMC vehicle were accurately predicted from the tear concentrations by using the in vivo ocular pharmacokinetic model. CMC vehicle improved the ocular delivery of tilisolol.     

Pharmacokinetics of recombinant human basic fibroblast growth factor in rabbits and mice serum and rabbits aqueous humor

AIM: To study the pharmacokinetics of recombinant human basic fibroblast growth factor (rhbFGF) in rabbits and mice after iv and postocular administration, and the changes of rhbFGF in rabbits aqueous humor after postocular administration. METHODS: After iv or postocular administration three doses of rhbFGF in rabbits and mice, rhbFGF concentration in serum and rabbit aqueous humor was determined by enzyme-linked immunosorbent assay. RESULTS: Serum concentration-time data of rabbits after iv administration of rhbFGF 1, 2, and 4 μg/kg were fitted to bi-exponential equations with half-lives of 0.9, 0.9, and 0.6 min for T1/2α and 7, 8, and 4.7 min for T1/2β. Plasma concentration-time data of mice after iv administration of rhbFGF 2.5, 5 and 10 μg/kg were fitted to bi exponential equations with half-lives of 0.4, 0.6, and 0.9 min for T1/2α　and 6, 5, and 7 min for T1/2β.The AUCs were linearly correlated to doses in both cases (rrabbit=0.997, rmouse=0.999). The serum concentrations of rhbFGF were very l     

Ocular Pharmacokinetic/Pharmacodynamic Modeling for Bunazosin After Instillation into Rabbits

PURPOSE: To develop a pharmacokinetic/pharmacodynamic (PK/PD) model for an alpha1-blocker (bunazosin) after instillation. The PK/PD model can predict both the drug concentrations in various ocular tissues and the hypotensive effect. METHODS: Bunazosin concentrations were determined with High Performance Liquid Chromatography (HPLC) in tear fluid, the aqueous humor, cornea, and iris-ciliary body after instillation or ocular injection into the anterior chamber in rabbits. After instillation of bunazosin in rabbits, intraocular pressure (IOP) was also determined with a pneumatic tonometer. The PK/PD parameters were estimated by fitting the concentration-time profiles and the hypotensive effect-time profiles to the developed PK/PD models using the MULTI (RUNGE) program. RESULTS: On the basis of the concentration-time profiles of bunazosin, a PK model, including seven compartments, was developed for examining the behavior of bunazosin after instillation. Then, two PK/ PD models for hypotensive effect of bunazosin were developed using an indirect response (model A) and the relationship between IOP and aqueous humor flow (model B). These models well described the concentration-time profiles and hypotensive effect-time profiles of bunazosin after instillation. CONCLUSIONS: This study is the first trial to develop a PK/PD model for an antiglaucoma agent using an indirect response and the relationship between IOP and aqueous humor flow.     

Relationship between the ocular and systemic disposition of flurbiprofen: the effect of altered protein dynamics at steady state

The differences in flurbiprofen disposition in the aqueous humor and the plasma were examined after systemic doses. Steady state plasma concentrations of flurbiprofen (20-60 micrograms/mL) were achieved via intravenous infusion to albino rabbits. Flurbiprofen demonstrated linear systemic kinetics throughout the dosing range, with constant body clearance and unbound fraction in plasma. At steady state, aqueous humor drug concentrations depended on the corresponding plasma drug concentration. Two clearance terms--CLS----O, the systemic clearance to ocular tissues, and CLO----S, the ocular clearance to systemic circulation--were used. After systemic doses, the drug concentration in the aqueous humor was related to that in the plasma as well as to the ratio of these two clearances. Flurbiprofen was extensively bound to plasma proteins and showed limited ocular distribution; its CLS----O to CLO----S ratio was very small. Thus, the concentration of flurbiprofen in the aqueous humor after systemic doses was lower than that obtained after ophthalmic doses. A plasmapheresis technique was utilized to lower the plasma protein concentrations to 60% of normal levels. As a consequence, flurbiprofen demonstrated reduced aqueous humor protein concentrations, increased unbound fractions in the plasma and the aqueous humor, elevated aqueous humor drug concentrations, and elevated total body clearance. The unbound body clearance stayed unchanged. Our study indicated that a drug should present a significant CLS----O/CLO----S ratio in order to achieve therapeutic concentrations in the eye via systemic doses. The drug-protein binding kinetics can be different between the plasma and the aqueous humor circulations. Because the ocular compartment is very small compared to the overall systemic distribution of flurbiprofen, it has little effect on the steady state systemic concentrations.     

Comparative Ocular Bioavailability and Efficacy of Topical Levofloxacin and Ofloxacin in Rabbits

Levofloxacin and ofloxacin are fluoroquinolone antibacterial agents with activity against a broad spectrum of Gram‐positive and Gram‐negative ocular pathogens. Levofloxacin is the pure S‐(?) isomer of ofloxacin, and is approximately twice as active as the R‐(+) isomer. Studies were conducted to measure the pharmacokinetics of levofloxacin and ofloxacin in the cornea and aqueous humor of the intact rabbit eye and also to determine the therapeutic efficacy of the two compounds for the treatment of experimental pseudomonas keratitis. A single ocular dose of 1.5% levofloxacin to intact rabbit eyes produced average maximum concentration (C_max) values in both cornea and aqueous humor that were approximately five times greater than that of 0.3% ofloxacin. Furthermore, concentrations of levofloxacin in corneas were maintained above the minimum inhibitory concentration 90% (MIC₉₀) for most ocular pathogens for more than 2 hours following a single topical dose. In a rabbit model of pseudomonas keratitis, dosing rabbits for 2 days with either 1.5% levofloxacin every 2 hours, or 0.3% ofloxacin every 30 minutes, resulted in the elimination of viable pseudomonas organisms from all treated rabbits. The results of these bioavailability and efficacy studies support the concept that a less frequent dosing regimen with 1.5% levofloxacin ophthalmic solution (every 2 hours) will be as effective as dosing 0.3% ofloxacin every 30 minutes for treatment of bacterial keratitis.     

Characterization of ocular pharmacokinetics of tilisolol after instillation into anesthetized rabbits

The purpose of this study was to characterize the ocular pharmacokinetics of a beta-blocker, tilisolol, after instillation into anesthetized rabbits using a mathematical model including a diffusion process. The samples were analyzed by HPLC. Anesthetized rabbit was used as a model of tear secretion deficiency. Anesthetized rabbits showed higher drug concentration in the tear fluid and aqueous humor after instillation than unanesthetized rabbits. A mathematical model including a diffusion process and in vivo penetration parameters well described the concentrations of tilisolol in the aqueous humor after instillation in anesthetized rabbits.     

Pharmacokinetics and efficacy of a ketorolac-loaded ocular coil in New Zealand white rabbits

Eye drops are considered standard practice for the delivery of ocular drugs. However, low patient compliance and low drug levels compromise its effectiveness. Our group developed a ketorolac-loaded ocular coil for sustained drug delivery up to 28 days. The aim of this study was to gain insight into the pharmacokinetics and efficacy of the ocular coil. The pharmacokinetics of the ketorolac-loaded ocular coil versus eye drops were tested in New Zealand White rabbits by repetitive sampling for 28 days. Efficacy of the ocular coil was also tested in New Zealand White rabbits. Ocular inflammation was induced where after the ocular coil was inserted, or eye drops, or no treatment was provided. The total protein concentration and cytokine levels were measured in tears, aqueous humor, and plasma at 4 h, 8 h, 24 h, 4 d, 7 d, 14 d, 21 d, and 28 d. Four h after inserting the ocular coil in the eye, ketorolac levels in aqueous humor and plasma were higher in the ocular coil group than in the eye drop group. Ketorolac released from the ocular coil could be detected up to 28 d in tears, up to 4 d in aqueous humor and up to 24 h in plasma. After inducing inflammation, both the ocular coil and eye drops were able to suppress prostaglandin E₂, TNFα and IL-6 levels in aqueous humor and plasma as compared to the group that received no treatment. To conclude, the ocular coil facilitated a sustained release of the drug and showed similar therapeutic benefit in suppressing post-operative inflammation as eye drops.     

A long-lasting hypotensive effect of topical diltiazem on the intraocular pressure in conscious rabbits

The effect of calcium channel blockers on intraocular pressure and aqueous humor dynamics remains still controversial, although preliminary evidence suggests that these drugs may be beneficial in the management of ocular hypertension and low-tension glaucoma. Having previously reported the ocular hypotensive effect of topical nifedipine and verapamil in albino rabbits, the original aim of the present work was to evaluate the effect of topical diltiazem on aqueous humor dynamics in this species. Intraocular pressure was measured with a manual applanation tonometer. The experiments examining the ocular actions of diltiazem were carried out in two stages. In the first one, short term effects of topical diltiazem on intraocular pressure were studied in groups of 13 albino rabbits receiving 8 different doses of the drug in order to obtain a dose-response curve. Tonographies were performed in 13 anaesthetized animals before and 90min after drug instillation. In a second phase, the persistence of the effect of diltiazem on intraocular pressure was examined in 6 groups of 10 rabbits each receiving three different doses of the drug. Topical diltiazem was found to lower intraocular pressure in a dose-related fashion. The maximum response to diltiazem was greater and the ED₅₀ lower than those previously reported for nifedipine and verapamil. In the tonographic study, diltiazem was shown to reduce the facility of aqueous humor outflow and inflow. Diltiazem exhibited a long lasting effect on intraocular pressure that was again dose-related. Depending on the dose administered, the calculated time necessary for the peak effect to be halved ranged from 0.6 to 7.0 days. Due to the intensity and the persistence of its intraocular pressure-lowering effect, diltiazem shows great potential for the treatment of glaucoma, since a daily or less frequent administration may be enough to control ocular hypertension. Received: 23 October 1996 / Accepted: 5 February 1997     

The effect of topical dihydroergocristine on the intraocular pressure in alpha-chymotrypsin-induced ocular hypertensive rabbits

Having previously reported that topical dihydroergocristine dose-dependently reduces intraocular pressure in ocular normotensive rabbits with a maximum response and potency higher than those of timolol and pilocarpine, the aim of the present work was to assess the effect of this drug in alpha-chymotrypsin-induced ocular hypertensive rabbits. Intraocular pressure was measured with a pneumatonometer. The experiments examining the effects of dihydroergocristine on intraocular pressure were conducted in 10 albino rabbits in which ocular hypertension was induced by intracameral injection of alpha-chymotrypsin. Intraocular pressure responses to drug vehicle and 5 different doses of topical dihydroergocristine were studied in order to obtain a dose-response curve. Tonographies were also performed in ocular hypertensive rabbits 2 h after vehicle and dihydroergocristine instillation to ascertain the actions of this drug on aqueous humor dynamics. Topical dihydroergocristine was found to lower intraocular pressure in alpha-chymotrypsin-induced ocular hypertensive rabbits in a dose-related manner, with the ED50 of the concentration-response curve very similar to that previously obtained in ocular normotensive rabbits. Data from tonographic studies indicate that dihydroergocristine reduces intraocular pressure in this animal model for glaucoma by decreasing the aqueous humor inflow. Our findings suggest that topical dihydroergocristine may be useful in the treatment of ocular hypertension.     

Kinetic disposition and distribution of timolol in the rabbit eye. A physiologically based ocular model

This paper presents a physiologically-based mathematical model which describes the disposition of timolol in the rabbit eye. In vitro uptake experiments were utilized to obtain estimates for the various transport and equilibrium tissue distribution coefficients. Two approaches were used to evaluate the uptake data. Initially, the ocular tissues and incubation medium were considered as well-stirred compartments. Alternatively, the iris and lens were viewed as geometric membranes, where the uptake of timolol was governed by simple passive diffusion of drug through the entire tissue. The results clearly indicate that the compartmental treatment of the lens is inappropriate. Consequently, the characterization of ocular drug distribution in the lens should involve a consideration of diffusion through the entire structure. No discernable differences, however, were observed for the iris using either approach, suggesting that the compartmental view may be a valid approximation in this case. In vivo concentration-time profiles were constructed for the cornea, iris, lens, aqueous and vitreous humors following topical dosing with a solution of timolol. Good agreement between the model-predicted and experimental data is observed for both the iris and aqueous humor. However, the magnitude of the iridal transport parameter, estimated from the uptake studies, was not sufficient to account for the early peak concentration observed for the iris. In this and most other ocular models, drug is assumed to enter the iris predominantly by exchange with the aqueous humor. To explain the relatively early peak time, an alternate route for drug entry is proposed. The existence of such a pathway is consistent with other reports in the literature, as well as the rapid peak levels observed here for both the vitreous humor and lens.     

Effects of topically applied liposomes on disposition of epinephrine and inulin in the albino rabbit eye

By virtue of the biocompatibility of their constituent phospholipids and of their ability to influence cell membrane permeability, liposomes are an attractive system for topical ocular drug delivery. The objective of this study was to investigate whether the ocular disposition of epinephrine and inulin in the albino rabbit was similarly affected following their encapsulation in multilamellar liposomes. Drug concentrations in tears, conjunctiva, cornea, iris plus ciliary body and aqueous humor were monitored at 30 min post-instillation of various preparations of each drug using radiotracer techniques. Liposomal drug entrapment was found to have opposite effects on the corneal and conjunctival absorption of epinephrine and inulin, epinephrine absorption was reduced by 50% whereas inulin absorption was increased 10 times. Quite unexpectedly, although inulin was detected in the uveal tract, none of it was detected in the aqueous humor when presented in liposomal form. These preliminary data suggest that while the corneal and conjunctival absorption of a drug can be modified by its entrapment in liposomes, its disposition in the intraocular tissues is unlikely to be controlled entirely by liposomes, since few, if any, of the liposomes that may be absorbed are expected to maintain their integrity while permeating the cornea.     

环孢素脂质体在家兔眼部的吸收与组织分布研究

目的 :以环孢素 (CsA)橄榄油滴眼液为对照制剂 ,考察家兔眼部应用CsA脂质体后 ,CsA在眼部的吸收及组织分布。方法 :2 7只家兔 ,分别多剂量应用 0 5 %CsA橄榄油滴眼液 ,中性脂质体和正电荷脂质体 ,并分别于用药后 0 5 ,1,2h后处死家兔 ,抽取房水 ,分离角膜、虹膜、巩膜、玻璃体和晶体。采用HPLC MS法测定各种组织中CsA的含量。结果 :2种脂质体制剂吸收进入眼组织中的CsA浓度 ,均高于橄榄油滴眼液 ,其中正电荷脂质体均有显著性差异 (P <0 0 5 ) ,而中性脂质体多数有显著性差异 (P <0 0 5 ) ,正电荷脂质体在组织中的平均药物浓度较中性脂质体高 ,但多数无显著性差异。结论 :脂质体可显著改善CsA在眼部吸收 ,提高CsA在眼部各组织的分布浓度     

Influence of emulsion droplet surface charge on indomethacin ocular tissue distribution

The aim of this study was to compare the corneal penetration of indomethacin from Indocollyre [a marketed hydro-poly(ethylene glycol) (PEG) ocular solution] to that of a negatively and a positively charged submicron emulsion. Male albino rabbits were separated randomly into three groups and each group (N = 15) was treated with either one drop of radiolabeled 0.1% Indocollyre, or 0.1% indomethacin positively or negatively charged submicron emulsion, respectively. The rabbits were sacrificed at selected time points and the eyes were enucleated. The eyes were dissected into the different tissues: cornea, conjunctiva, aqueous humor, iris, lens, vitreous, sclera, and retina. The samples were weighed before radioactivity counting. Regardless of the preparation instilled, the highest concentration of indomethacin was achieved in the cornea followed by conjunctiva, sclera retina, and aqueous humor. However, the positively charged emulsion provided significantly higher drug levels than the control solution and negatively charged emulsion only in the aqueous humor and sclera-retina. Furthermore, the spreading coefficient of the positively charged emulsion on cornea is four times higher than that of the negatively charged emulsion. It was therefore deduced that the positively charged submicron emulsions have better wettability properties on the cornea compared to either saline or the negatively charged emulsion. The positive charge may prolong the residence time of the drop on the epithelial layer of the cornea and thus enable better drug penetration through the cornea to the internal tissues of the eye, as confirmed by the animal studies.     

Ocular and systemic bioavailability of ophthalmic flurbiprofen

Flurbiprofen, a nonsteroidal antiinflammatory agent which is not ocularly metabolized, was employed as a probe compound to investigate the drug kinetic relationship between systemic and ocular humoral circulation. The ocular and systemic bioavailabilities of topically applied flurbiprofen were also quantitated. Anesthetized albino female rabbits received flurbiprofen doses intracamerally, topically, and intravenously at 2 to 4 week intervals. Aqueous humor and plasma were used as the sampling compartments. Plasma clearance values of flurbiprofen were 6.77 and 7.87 ml/min, after 6-mg and 208-micrograms intravenous doses, respectively. These values were not significantly different and indicated no dose-dependent disposition kinetics over a 30-fold dose range. Both ocular and systemic flurbiprofen dispositions followed a biexponential pattern with a rapid distribution phase. The systemic and ocular distribution half-lives of flurbiprofen were 12 min and 15 min, respectively. The plasma elimination half-life was 74 min and the aqueous humor elimination half-life was 93 min. The latter approximated the turnover rate of aqueous humor and suggested that aqueous humor drainage was the major process of flurbiprofen elimination from the globe. About 99% of flurbiprofen is bound to plasma protein. At distribution equilibrium, the plasma and aqueous humor concentrations of flurbiprofen differed by a hundredfold, suggesting that only free drug entered the aqueous humor after the administration of a systemic dose. In the ophthalmic studies, right eyes were instilled with 50 microliters of 0.3% flurbiprofen in saline (dose = 150 micrograms), and left eyes were instilled with 50 microliters of 0.15% flurbiprofen in saline (dose = 75 micrograms). When the area of the aqueous humor concentration-versus-time curve values was normalized by the administration dose, the 75-micrograms dose was 30% more available to ocular tissues than was the 150-micrograms dose. This demonstrated a disproportionate relationship between the administered dose and the fraction absorbed. The intracameral dose was considered to be completely bioavailable for intraocular effects. The ocular bioavailability of the ophthalmic dose was defined by using intracameral administration as a standard measurement. The ocular bioavailabilities of the 75-micrograms and 150-micrograms topical flurbiprofen doses were 10% and 7%, respectively. Systemic bioavailability after topical administration of 225 micrograms of flurbiprofen was 74%.     

Pharmacokinetics of falintolol II. Absorption, distribution and elimination from tissues and organs following ocular administration and intravenous injection of falintolol in albino rabbits

The absorption, distribution and elimination of falintolol maleate was studied in various ocular and extraocular tissues and organs following ocular instillation, intravenous injection of a 0.5% 14C-falintolol ophthalmic solution and repeated ocular instillations of a 1% non-labeled falintolol ophthalmic solution into albino New Zealand rabbits. Falintolol was distributed in all studied tissues and organs after both routes of administration. After ocular instillation, levels of total radioactivity were distinctly higher in ocular tissues than after intravenous injection. Thus, the level was 475 times more important in cornea, 72 times in aqueous humor and 36 times in iris and ciliary body after ocular instillation. On the other hand, levels of total radioactivity in extraocular tissues and organs were 30-50% higher after intravenous injection compared to ocular instillation of the same dose. Peak levels of total radioactivity were generally achieved between 30 min and 1 h after ocular instillation, while 1.5 h after intravenous injection an increase in the declining part of the curve occurred. This increase, characteristic of an enterohepatic reabsorption, was also observed in blood and plasma 1 h after intravenous injection. Urinary elimination was the major means of excretion since 79.6% of total radioactivity was found in urine 6 h after intravenous injection and 74.5% 12 h after ocular instillation. But after ocular instillation, only 5% was excreted as unchanged falintolol. Whatever the route of administration, after single or repeated application, no drug accumulation was evident.