The effect of different ophthalmic vehicles on the activity of tropicamide in man

3: Final Report on the Safety Assessment of Diisopropanolamine, Triisopropanolamine, Isopropanolamine, and Mixed Isopropanolamine

Diisopropanolamine, Triisopropanolamine, Isopropanolamine, and Mixed Isopropanolamine are used as water-soluble emulsifiers and neutralizers in cosmetic products at concentrations up to 1%. In animal studies these ingredients were slightly toxic to practically nontoxic to rats and guinea pigs via acute oral administration. Triisopropanolamine was relatively nontoxic to rats in the two subchronic oral studies. These ingredients were moderate skin irritants for rabbits. All four ingredients, when tested at 100% concentrations, were severe ocular irritants in rabbits. Products containing small amounts (-1%) of Diisopropanolamine or Triisopropanolamine were not ocular irritants in rabbits. The Triisopropanolamine salt was not mutagenic in Aspergillus nidulans. Diisopropanolamine and Isopropanolamine at concentrations of 2% did not induce allergic contact dermatitis or photoallergic dermatitis in humans. Clinical studies on cosmetic products containing no more than 1% Diisopropanolamine or 1.1% Triisopropanolamine were minimal skin irritant and contact sensitizers. It is concluded that Diisopropanolamine, Triisopropanolamine, Isopropanolamine, and Mixed Isopropanolamine are safe as cosmetic ingredients in the present practices of use and concentration. The Isopropanolamines should not be used in products containing N-nitrosating agents.

Ocular preparations: the formulation approach

The main aim of pharmacotherapeutics is the attainment of an effective drug concentration at the intended site of action for a sufficient period of time to elicit the response. A major problem being faced in ocular therapeutics is the attainment of an optimal concentration at the site of action. Poor bioavailability of drugs from ocular dosage forms is mainly due to the tear production, non-productive absorption, transient residence time, and impermeability of corneal epithelium. This article reviews: (1) the barriers that decrease the bioavailability of an ophthalmic drug; (2) the objectives to be considered in producing optimal formulations; and (3) the approaches being used to improve the corneal penetration of a drug molecule and delay its elimination from the eye. The focus of this review is on the recent developments in topical ocular drug delivery systems, the rationale for their use, their drug release mechanism, and the characteristic advantages and limitations of each system. In addition, the review attempts to give various analytical procedures including the animal models and other models required for bioavailability and pharmacokinetic studies. The latter can aid in the design and predictive evaluation of newer delivery systems. The dosage forms are divided into the ones which affect the precorneal parameters, and those that provide a controlled and continuous delivery to the pre- and intraocular tissues. The systems discussed include: (a) the commonly used dosage forms such as gels, viscosity imparting agents, ointments, and aqueous suspensions; (b) the newer concept of penetration enhancers, phase transition systems, use of cyclodextrins to increase solubility of various drugs, vesicular systems, and chemical delivery systems such as the prodrugs; (c) the developed and under-development controlled/continuous drug delivery systems including ocular inserts, collagen shields, ocular films, disposable contact lenses, and other new ophthalmic drug delivery systems; and (d) the newer trends directed towards a combination of drug delivery technologies for improving the therapeutic response of a non-efficacious drug. The fruitful resolution of the above-mentioned technological suggestions can result in a superior dosage form for both topical and intraocular ophthalmic application.

In situ gelling xyloglucan formulations for sustained release ocular delivery of pilocarpine hydrochloride

Thermoreversible gels formed in situ by aqueous solutions of an enzyme-degraded xyloglucan polysaccharide were evaluated as sustained release vehicles for the ocular delivery of pilocarpine hydrochloride. In vitro release of pilocarpine from gels formed by warming xyloglucan sols (1.0, 1.5 and 2.0% w/w) to 34 degrees C followed root-time kinetics over a period of 6 h. The miotic responses in rabbit following administration of xyloglucan sols were compared with those from in situ gelling Pluronic F127 sols and from an aqueous buffer solution containing the same drug concentration. Sustained release of pilocarpine was observed with all gels, the duration of miotic response increasing with increase of xyloglucan concentration. The degree of enhancement of miotic response following sustained release of pilocarpine from the 1.5% w/w xyloglucan gel was similar to that from a 25% w/w Pluronic F127 gel.

Topical interleukin 1 receptor antagonist promotes corneal transplant survival

BACKGROUND

Interleukin (IL)-1 is a potent proinflammatory cytokine that plays a critical role in initiating and maintaining immunogenic inflammation. We performed a series of experiments to determine whether the topical application of IL-1 receptor antagonist (IL-1ra) can prolong corneal transplant survival in the murine model of orthotopic allotransplantation.

METHODS

For all experiments, C57BL/6 corneas were transplanted into BALB/c (major histocompatibility and minor histocompatibility-disparate) eyes. "High-risk" transplants were transplants that had been sutured into BALB/c recipient beds with corneal neovascularization induced by placement of three interrupted sutures in the host cornea 2 weeks earlier. Both risk groups were divided in a masked fashion into treatment subgroups that received either 20 mg/ml of IL-1ra mixed in 0.2% sodium hyaluronate vehicle (n=28) or placebo alone (n=25). All transplants were evaluated for 8 weeks after surgery for signs of rejection. At the end of follow-up, corneal specimens were processed for enumeration of Langerhans cells and histopathological evaluation.

RESULTS

Survival rates of both normal-risk and high-risk transplants increased significantly among the IL-1ra-treated animals compared with untreated controls by both stratified Mantel-Haenszel (P=0.02) and Kaplan-Meier survival (P=0.03) analyses. Furthermore, both normal- and high-risk IL-1ra-treated grafts had significantly less inflammation and Langerhans cells infiltration compared with untreated controls.

CONCLUSIONS

Topical treatment with IL-1ra has a significantly positive effect in promoting corneal allograft survival.

Comparative evaluation of Butea frondosa and flurbiprofen for ocular anti-inflammatory activity in rabbits

The roots and leaves of the plant Butea frondosa were evaluated for ocular anti-inflammatory activity on the subacute model of ocular inflammation in rabbits. The arkas (liquid preparations obtained by distillation of certain liquids or drugs soaked in water, using the Arka-Yantra or any other convenient modern distillation apparatus) were prepared using the roots and leaves of the plant. The arkas were formulated as gels using Pluronic F-127 (PF-127) 30% w/w as the polymer. The anti-inflammatory activity of the preparations were assessed by determining their effects on elevated intraocular pressure consequent to breakdown of blood/aqueous humour barrier. A commercial eyedrop of flurbiprofen 0.03% w/w was used to compare the ocular anti-inflammatory activity of the arkas of the plant. A marketed root arka was included in the study for comparison. The anti-inflammatory activity of the arkas formulated as gels were compared with flurbiprofen gel prepared using the same polymer. The changes in intraocular pressure were monitored at various time intervals after a single dose administration of the aqueous as well as gel formulations. In multiple dose studies the aqueous preparations were administered three times a day, while the gels were administered once a day up to day 30 and the intraocular pressure was monitored on different days post-administration. The findings reveal statistically significant differences (P < 0.05) between the arkas of the plant and the commercial eyedrop of flurbiprofen. The arkas of the plant proved to be better than the eyedrop of flurbiprofen, while with respect to gels, the intraocular pressure monitored at various time intervals revealed no statistically significant difference (P > 0.05) between the gel formulations. However, the changes in intraocular pressure monitored on different days post-administration until day 30, demonstrated that the gel produced from B. frondosa leaves arka was superior to all the other gels with respect to the extent of reduction of elevated intraocular pressure elicited experimentally.

Effects of epinephrine pretreatment and solution pH on ocular and systemic absorption of ocularly applied timolol in rabbits

The ratio between ocular and systemic drug concentrations describes the relative safety of ophthalmic dosage forms of the same drug in terms of its systemic side effects. In this study, we evaluated the effects of epinephrine pretreatment and solution pH on the aqueous humor:plasma and iris-ciliary body:plasma ratios of peak timolol concentrations after ocular application of timolol. Timolol eyedrops (5 mg/mL, 25 microL) were applied ocularly in pigmented rabbits. Raising pH of the eyedrops from 6.2 to 7.5 did not affect the ratio between ocular and systemic peak drug concentrations, since both ocular and systemic concentrations of timolol were increased. Administration of epinephrine (20 mg/mL, 50 microL) 5 min prior to timolol eyedrop administration reduced the peak timolol concentrations in plasma 65-80%. Epinephrine did not affect the ocular concentrations of timolol. The decreased peak concentrations in plasma were due to the conjunctival and nasal vasoconstricting effects of epinephrine and to the subsequent slower absorption of timolol. Our study demonstrates that compared with currently available eyedrops (pH 6.9), the ocular:systemic concentration ratio of ophthalmic timolol can be improved four- to sixfold in rabbits by combining epinephrine-induced conjunctival and nasal vasoconstriction and improved ocular absorption from pH 7.5 eyedrops.

Precorneal residence times of sodium hyaluronate solutions studied by quantitative gamma scintigraphy

Sodium hyaluronate solutions have been advocated in the management of a variety of dry-eye states. By virtue of their non-Newtonian rheological properties, formulations exhibiting high zero-shear viscosities may be used as an artificial tear with the expectation of prolonged precorneal residence times and improved tolerance. Quantitative gamma scintigraphy was used to evaluate the residence times of 0.2% and 0.3% sodium hyaluronate solutions and a polymer-free solution of buffered saline in 12 patients with keratoconjunctivitis sicca and a group of six normal volunteers. Using several indices of residence time, mean values for the sodium hyaluronate solutions were significantly longer than those for buffered saline. Parallel changes in tear film thickness were also demonstrated using a technique based on laser interferometry.

Topical ocular drug delivery: recent developments and future challenges

Existing ocular drug delivery systems are fairly primitive and inefficient, but the stage is set for the rational design of newer and significantly improved systems. The focus of this review is on recent developments in topical ocular drug delivery systems relative to their success in overcoming the constraints imposed by the eye and to the improvements that have yet to be made. In addition, this review attempts to place in perspective the importance of pharmacokinetic modeling, ocular drug pharmacokinetic and bioavailability studies, and choice of animal models in the design and evaluation of these delivery systems. Five future challenges are perceived to confront the field. These are: (a) The extent to which the protective mechanisms of the eye can be safely altered to facilitate drug absorption, (b) Delivery of drugs to the posterior portion of the eye from topical dosing, (c) Topical delivery of macromolecular drugs including those derived from biotechnology, (d) Improved technology which will permit non-invasive monitoring of ocular drug movement, and (e) Predictive animal models in all phases of ocular drug evaluation.

Studies on the conjugation of leukotriene B4 with proteins for development of a radioimmunoassay for leukotriene B4

Leukotriene B4 (LTB4) (I) has been converted to its N-(3-amino-propyl)amide derivative (III) and to its hydrazide derivative (VII) via LTB4 delta-lactone. The amide (III) was coupled with Bovine Serum Albumin using 1,5-difluoro-2,4-dinitrobenzene as coupling agent. The hydrazide (VII), was coupled with Hemocyanin (Keyhole Limpet) (KLH) using 6-N-maleimidohexanoic acid chloride as coupling agent.