Ocular absorption behavior of palmitoyl tilisolol, an amphiphilic prodrug of tilisolol, for ocular drug delivery

Ocular prodrugs: Attributes and challenges

Ocular drug delivery is one of the most attention-grabbing and challenging endeavors among the numerous existing drug delivery systems. From a drug delivery point of view, eye is an intricate organ to investigate and explore. In spite of many limitations, advancements have been made with the intention of improving the residence time or permeation of the drug in the ocular region. Poor bioavailability of topically administered drugs is the major issue pertaining to ocular drug delivery. Several efforts have been made towards improving precorneal residence time and corneal penetration, e.g. iontophoresis, prodrugs and ion-pairing, etc. Prodrug approach (chemical approach) has been explored by the formulation scientists to optimize the physicochemical and biochemical properties of drug molecules for improving ocular bioavailability. Formulation of ocular prodrugs is a challenging task as they should exhibit optimum chemical stability as well as enzymatic liability so that they are converted into parent drug after administration at the desired pace. This review will encompass the concept of derivatization and recent academic and industrial advancements in the field of ocular prodrugs. The progression in prodrug designing holds a potential future for ophthalmic drug delivery.

Effect of in vitro transcorneal approach of aceclofenac eye drops through excised goat, sheep, and buffalo corneas

The current study involves the evaluation of factors that influence the transcorneal permeation of aqueous drops of aceclofenac ophthalmic formulation through freshly excised goat, sheep, and buffalo corneas. Aceclofenac formulation with different concentrations 0.1-0.5% (w/v) and with different pH and different preservatives, was taken into account. The amount of drug permeated from different formulations was estimated using an Franz diffusion cell. A linear increase in drug permeation was observed with increase in pH (5.5 to 7.4). The apparent permeability coefficient was found to be maximum 15.01 ± 0.45 on goat cornea and maximum transport of aceclofenac was observed at physiological pH of tears (i.e., 7). The results advocate that aceclofenac 0.5% (w/v) ophthalmic solution (pH 7.0) containing BAK (0.01%) provides maximum in vitro ocular permeability through goat, sheep, and buffalo corneas.

Biodistribution and pharmacokinetics of O-palmitoyl tilisolol, a lipophilic prodrug of tilisolol, after intravenous administration in rats

The purpose of this study was to modify the biodistribution and pharmacokinetics of tilisolol, a beta-blocker, using the palmitoyl prodrug approach. After intravenous administration of tilisolol and O-palmitoyl tilisolol in rats, drug concentrations were determined in blood, bile, urine, and several tissues. The concentration-time profiles of tilisolol and O-palmitoyl tilisolol were analyzed pharmacokinetically. The blood concentrations of O-palmitoyl tilisolol after intravenous administration of O-palmitoyl tilisolol were about 10-fold higher than those of tilisolol after intravenous administration of tilisolol. The biliary excretion rates of O-palmitoyl tilisolol and tilisolol after intravenous administration of O-palmitoyl tilisolol were about 10- to 100-fold larger than those of tilisolol after intravenous administration of tilisolol. In addition, the hepatic uptake clearance of O-palmitoyl tilisolol after intravenous administration of O-palmitoyl tilisolol was 3.6-fold higher than that of tilisolol after the intravenous administration of tilisolol. In the in vitro experiments, it was demonstrated that the distribution ratios between blood cells and plasma (blood/plasma) of O-palmitoyl tilisolol and tilisolol was 95.7 and 55.5%, respectively. These findings suggest that O-palmitoyl tilisolol exists as a binding form with biological components, especially blood cells, in systemic circulation. In conclusion, the palmitoyl prodrug approach is useful as a drug delivery system to deliver the parent drug to the liver.

Controlled release and ocular absorption of tilisolol utilizing ophthalmic insert-incorporated lipophilic prodrugs

To control ocular drug delivery, the O-butyryl ester prodrug of tilisolol (BUTL) and the O-palmitoyl ester prodrug of tilisolol (PalTL) were incorporated into an ophthalmic insert. The released TL from BUTL inserts and PalTL inserts in pH 7.4 phosphate-buffered saline until 5 h were approximately 25% and 3% of that from TL inserts, respectively. In addition, BUTL was also released from BUTL inserts. However, PalTL was not released from the PalTL insert. The release of drugs from TL inserts and BUTL inserts was little affected by the addition of bovine serum albumin (BSA) in pH 7.4 phosphate-buffered saline. In contrast, the release of drugs from PalTL inserts were enhanced by the addition of BSA. After application of TL, BUTL, and PalTL inserts to the rabbit eye, the aqueous humor concentration of TL was prolonged compared with TL instillation, and the plasma concentration of TL was much lower than that of TL instillation. The ratios of the area under the TL concentration-time curve (AUC) in the aqueous humor to AUC in the plasma (AUC(aqueous)/AUC(plasma)) after application of BUTL until 8 h were 3.1-fold and 3.8-fold higher than those of the TL insert and PalTL insert, respectively.

Sustained ocular delivery of tilisolol to rabbits after topical administration or intravitreal injection of lipophilic prodrug incorporated in liposomes

To improve the retention time of tilisolol in the precorneal area or vitreous body, we prepared liposomes incorporating the O-palmitoyl prodrug of tilisolol. O-Palmitoyl tilisolol was completely incorporated in the liposomes. After topical administration of O-palmitoyl tilisolol liposomes to the rabbit eye, O-palmitoyl tilisolol rapidly disappeared from the tear fluid. The inclusion of 2% carmellose sodium slightly prolonged the retention of O-palmitoyl tilisolol in the tear fluid. After intravitreal injection of O-palmitoyl tilisolol liposomes, there was a relatively prolonged retention of O-palmitoyl tilisolol in the vitreous body. At 24 and 48 h after intravitreal injection of O-palmitoyl tilisolol liposomes, the tilisolol concentration in the vitreous body was significantly higher compared with the concentration after intravitreal injection of tilisolol liposomes.