Understanding dexamethasone kinetics in the rabbit tear fluid : Drug release and clearance from solution, suspension and hydrogel formulations

Rapid precorneal loss of topically applied eye drops limits ocular drug absorption. Controlling release and precorneal residence properties of topical formulations may improve ocular drug bioavailability and duration of action. In this study, we evaluated in vivo ocular pharmacokinetics of dexamethasone in rabbits after application of a drug solution (0.01%), suspension (Maxidex (R) 0.1%), and hydrogels of 2-hydroxyethyl methacrylate (HEMA) and acrylic acid (AAc) copolymers. The rabbits received a single eyedrop (solution or suspension) or dexamethasone-loaded hydrogel topically. Dexamethasone in tear fluid was sampled with glass capillaries and quantitated by LC-MS/MS. Higher dexamethasone exposure (AUC) in the tear fluid was observed with the suspension (approximate to 3.6-fold) and hydrogel (12.8-fold) as compared to the solution. During initial 15 min postapplication, the highest AUC of dissolved dexamethasone was seen after hydrogel application (368 min*mu g/ mL) followed by suspension (109.9 min*mu g/mL) and solution (28.7 min*mu g/mL. Based on kinetic simulations, dexamethasone release from hydrogels in vivo and in vitro is comparable. Our data indicate that prolonged exposure of absorbable dexamethasone in tear fluid is reached with hydrogels and suspensions. Pharmacokinetic understanding of formulation behavior in the lacrimal fluid helps in the design of dexamethasone delivery systems with improved ocular absorption and prolonged duration of action.Peer reviewe

Partitioning and Spatial Distribution of Drugs in Ocular Surface Tissues

Ocular drug absorption after eye drop instillation has been widely studied, but partitioning phenomena and spatial drug distribution are poorly understood. We investigated partitioning of seven beta-blocking drugs in corneal epithelium, corneal stroma, including endothelium and conjunctiva, using isolated porcine tissues and cultured human corneal epithelial cells. The chosen beta-blocking drugs had a wide range (-1.76-0.79) of n-octanol/buffer solution distribution coefficients at pH 7.4 (Log D-7.4). In addition, the ocular surface distribution of three beta-blocking drugs was determined by matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS) after their simultaneous application in an eye drop to the rabbits in vivo. Studies with isolated porcine corneas revealed that the distribution coefficient (K-p) between the corneal epithelium and donor solution showed a positive relationship and good correlation with Log D-7.4 and about a 50-fold range of K-p values (0.1-5). On the contrary, K-p between corneal stroma and epithelium showed an inverse (negative) relationship and correlation with Log D-7.4 based on a seven-fold range of K-p values. In vitro corneal cell uptake showed a high correlation with the ex vivo corneal epithelium/donor K-p values. Partitioning of the drugs into the porcine conjunctiva also showed a positive relationship with lipophilicity, but the range of K-p values was less than with the corneal epithelium. MALDI-IMS allowed simultaneous detection of three compounds in the cornea, showed data in line with other experiments, and revealed uneven spatial drug distribution in the cornea. Our data indicate the importance of lipophilicity in defining the corneal pharmacokinetics and the K-p values are a useful building block in the kinetic simulation models for topical ocular drug administration.Peer reviewe

Simultaneous Determination of Procainamide and N-acetylprocainamide in Rat Plasma by Ultra-High-Pressure Liquid Chromatography Coupled with a Diode Array Detector and Its Application to a Pharmacokinetic Study in Rats

A simple, sensitive, and reliable reversed-phase, Ultra-High-Pressure Liquid Chromatography (UHPLC) coupled with a Diode Array Detector (DAD) method for the simultaneous determination of Procainamide (PA) and its major metabolite, N-acetylprocainamide (NAPA), in rat plasma was developed and validated. A simple deproteinization method with methanol was applied to the rat plasma samples, which were analyzed using UHPLC equipped with DAD at 280 nm, and a Synergi™ 4 µm polar, reversed-phase column using 1% acetic acid (pH 5.5) and methanol (76:24, v/v) as eluent in isocratic mode at a flow rate 0.2 mL/min. The method showed good linearity (r2 > 0.998) over the concentration range of 20–100,000 and 20–10,000 ng/mL for PA and NAPA, respectively. Intra- and inter-day accuracies ranged from 97.7 to 110.9%, and precision was <10.5% for PA and 99.7 to 109.2 and <10.5%, respectively, for NAPA. The lower limit of quantification was 20 ng/mL for both compounds. This is the first report of the UHPLC-DAD bioanalytical method for simultaneous measurement of PA and NAPA. The most obvious advantage of this method over previously reported HPLC methods is that it requires small sample and injection volumes, with a straightforward, one-step sample preparation. It overcomes the limitations of previous methods, which use large sample volume and complex sample preparation. The devised method was successfully applied to the quantification of PA and NAPA after an intravenous bolus administration of 10 mg/kg procainamide hydrochloride to rats

Physiologically-Based Pharmacokinetic Modeling for Drug-Drug Interactions of Procainamide and N-Acetylprocainamide with Cimetidine, an Inhibitor of rOCT2 and rMATE1, in Rats

Previous observations demonstrated that cimetidine decreased the clearance of procainamide (PA) and/or N-acetylprocainamide (NAPA; the primary metabolite of PA) resulting in the increased systemic exposure and the decrease of urinary excretion. Despite an abundance of in vitro and in vivo data regarding pharmacokinetic interactions between PA/NAPA and cimetidine, however, a mechanistic approach to elucidate these interactions has not been reported yet. The primary objective of this study was to construct a physiological model that describes pharmacokinetic interactions between PA/NAPA and cimetidine, an inhibitor of rat organic cation transporter 2 (rOCT2) and rat multidrug and toxin extrusion proteins (rMATE1), by performing extensive in vivo and in vitro pharmacokinetic studies for PA and NAPA performed in the absence or presence of cimetidine in rats. When a single intravenous injection of PA HCl (10 mg/kg) was administered to rats, co-administration of cimetidine (100 mg/kg) significantly increased systemic exposure and decreased the systemic (CL) and renal (CLR) clearance of PA, and reduced its tissue distribution. Similarly, cimetidine significantly decreased the CLR of NAPA formed by the metabolism of PA and increased the AUC of NAPA. Considering that these drugs could share similar renal secretory pathways (e.g., via rOCT2 and rMATE1), a physiologically-based pharmacokinetic (PBPK) model incorporating semi-mechanistic kidney compartments was devised to predict drug-drug interactions (DDIs). Using our proposed PBPK model, DDIs between PA/NAPA and cimetidine were successfully predicted for the plasma concentrations and urinary excretion profiles of PA and NAPA observed in rats. Moreover, sensitivity analyses of the pharmacokinetics of PA and NAPA showed the inhibitory effects of cimetidine via rMATE1 were probably important for the renal elimination of PA and NAPA in rats. The proposed PBPK model may be useful for understanding the mechanisms of interactions between PA/NAPA and cimetidine in vivo

A Novel Ferroptosis Inhibitor UAMC-3203, a Potential Treatment for Corneal Epithelial Wound

Corneal wound, associated with pain, impaired vision, and even blindness, is the most common ocular injury. In this study, we investigated the effect of a novel ferroptosis inhibitor, UAMC-3203 (10 nM–50 µM), in corneal epithelial wound healing in vitro in human corneal epithelial (HCE) cells and ex vivo using alkali-induced corneal wounded mice eye model. We evaluated in vivo acute tolerability of the compound by visual inspection, optical coherence tomography (OCT), and stereomicroscope imaging in rats after its application (100 µM drug solution in phosphate buffer pH 7.4) twice a day for 5 days. In addition, we studied the partitioning of UAMC-3203 in corneal epithelium and corneal stroma using excised porcine cornea. Our study demonstrated that UAMC-3203 had a positive corneal epithelial wound healing effect at the optimal concentration of 10 nM (IC50 value for ferroptosis) in vitro and at 10 µM in the ex vivo study. UAMC-3203 solution (100 µM) was well tolerated after topical administration with no signs of toxicity and inflammation in rats. Ex-vivo distribution study revealed significantly higher concentration (~12–38-fold) and partition coefficient (Kp) (~52 times) in corneal epithelium than corneal stroma. The UAMC-3203 solution (100 µM) was stable for up to 30 days at 4 °C, 37 °C, and room temperature. Overall, UAMC-3203 provides a new prospect for safe and effective therapy for corneal wounds

A Novel Ferroptosis Inhibitor UAMC-3203, a Potential Treatment for Corneal Epithelial Wound

Corneal wound, associated with pain, impaired vision, and even blindness, is the most common ocular injury. In this study, we investigated the effect of a novel ferroptosis inhibitor, UAMC-3203 (10 nM–50 µM), in corneal epithelial wound healing in vitro in human corneal epithelial (HCE) cells and ex vivo using alkali-induced corneal wounded mice eye model. We evaluated in vivo acute tolerability of the compound by visual inspection, optical coherence tomography (OCT), and stereomicroscope imaging in rats after its application (100 µM drug solution in phosphate buffer pH 7.4) twice a day for 5 days. In addition, we studied the partitioning of UAMC-3203 in corneal epithelium and corneal stroma using excised porcine cornea. Our study demonstrated that UAMC-3203 had a positive corneal epithelial wound healing effect at the optimal concentration of 10 nM (IC50 value for ferroptosis) in vitro and at 10 µM in the ex vivo study. UAMC-3203 solution (100 µM) was well tolerated after topical administration with no signs of toxicity and inflammation in rats. Ex-vivo distribution study revealed significantly higher concentration (~12–38-fold) and partition coefficient (Kp) (~52 times) in corneal epithelium than corneal stroma. The UAMC-3203 solution (100 µM) was stable for up to 30 days at 4 °C, 37 °C, and room temperature. Overall, UAMC-3203 provides a new prospect for safe and effective therapy for corneal wounds