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

Molecular design for enhancement of ocular penetration

Over the past two decades, many oral drugs have been designed in consideration of physicochemical properties to attain optimal pharmacokinetic properties. This strategy significantly reduced attrition in drug development owing to inadequate pharmacokinetics during the last decade. On the other hand, most ophthalmic drugs are generated from reformulation of other therapeutic dosage forms. Therefore, the modification of formulations has been used mainly as the approach to improve ocular pharmacokinetics. However, to maximize ocular pharmacokinetic properties, a specific molecular design for ocular drug is preferable. Passive diffusion of drugs across the cornea membranes requires appropriate lipophilicity and aqueous solubility. Improvement of such physicochemical properties has been achieved by structure optimization or prodrug approaches. This review discusses the current knowledge about ophthalmic drugs adapted from systemic drugs and molecular design for ocular drugs. I propose the approaches for molecular design to obtain the optimal ocular penetration into anterior segment based on published studies to date.

Synthesis and stability of two indomethacin prodrugs

The purpose of this study was to synthesize and study the in vitro enzymatic and non-enzymatic hydrolysis of indomethacin-TEG ester and amide prodrugs. It was found that the ester conjugate 10 was comparatively stable between pH 3 and 6 (half-life>90h), with a half-life equal to 5.2h in 80% buffered plasma. In contrast, the amide conjugate 12 appeared to be stable over the entire pH range studied with the only observed degradation being cleavage of the indolic N-4-chlorobenzoyl moiety.

Minimizing systemic absorption of topically administered ophthalmic drugs

Due to absorption several ocularly applied medications give rise to systemic side-effects. The problem of systemic drug absorption should be taken into account in designing ocular drug and dosage forms so that oculospecificity of the medications is optimized. In this review we summarize the current knowledge about the systemic absorption of ocularly applied topical drugs. Special emphasis is directed to the methods that can be used to minimize systemic absorption and increase the oculospecificity of drugs, e.g., reducing volume and increasing viscosity of eyedrops, controlling drug release from depot preparations, prodrug-derivatization, and addition of vasoconstrictive agents.

Effect of induced hypoalbuminemia on distribution, total clearance and unbound clearance of piroxicam in vivo in the rat

The influence of decreased albumin concentration on the pharmacokinetic behaviour of Piroxicam was studied in vivo in rats that had undergone plasmapheresis. Reductions of approximately 25% and 50% in the plasma albumin concentration were achieved, the former in rats not given plasma expander, the latter in animals given Ficol-70 as a plasma expander. The unbound fraction of Piroxicam in plasma and the apparent volume of distribution at steady state experienced a statistically significant increase where the albumin concentration was reduced. The average total plasma clearance rose with the increase in fu, between the control (6.3 +/- 2.4 ml/h) and plasmapheretic groups (11.1 +/- 4 ml/h), in accordance with predictions of the 'well-stirred' and 'parallel-tube' models, but no statistically significant differences were found between the two groups, perhaps because of the great interindividual variability associated with this parameter. The total plasma clearance value of the Ficol group (5.4 +/- 2.2 ml/h) was close to that of the control group, despite the high increase in the unbound fraction in plasma. Alterations in the uptake process in the liver due to the high level of induced hypoalbuminemia may have occurred.

Argon laser-induced ocular hypertension: animal model of ocular inflammation

There is substantial evidence that prostaglandins (PG's) mediate acute elevations of intraocular pressure (IOP) due to laser irradiation of the iris. In the present study, we determined the optimal laser parameters needed to produce the maximal rise in IOP in anesthetized rabbits. Application of argon laser (0.75 watts, 0.5 sec. duration, and 8 spots of 500 micron size) to the iris of pigmented rabbits elicited an acute rise in IOP and miosis accompanied by an increase in aqueous protein concentration. This response was followed by a delayed ocular hypotension that lasted for more than 3 days and returned to baseline by day 5. The onset of ocular hypertension occurred within 15 min. and remained elevated for at least 90 min. The laser induced rise in IOP was related more to the number of laser spots applied to the iris than to the intensity of the total laser energy utilized. Pretreatment with either indomethacin or flurbiprofen produced a dose dependent inhibition of ocular hypertensive response and significantly reduced aqueous protein concentration. Indomethacin (0.01-30 mg/kg) was administered intraperitonially 1 hr. before laser treatment and flurbiprofen (0.03-0.3%) was administered topically 45 and 15 min. prior to laser application. The hypertensive response was reduced by more than 90% of control after both drugs, whereas the delayed hypotension was significantly antagonized only at the highest dose of indomethacin. Neither indomethacin nor flurbiprofen altered the maximum miotic response to laser irradiation of the iris. However, 0.3% flurbiprofen and 30 mg/kg indomethacin significantly increased the recovery rate of the miotic pupil. The results of this study support the contention that argon laser induced ocular hypertension may provide a quantitative assessment of inhibition of prostaglandin mediated responses.