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

Effect of viscosity on tear drainage and ocular residence time

PURPOSE

An increase in residence time of dry eye medications including artificial tears will likely enhance therapeutic benefits. The drainage rates and the residence time of eye drops depend on the viscosity of the instilled fluids. However, a quantitative understanding of the dependence of drainage rates and the residence time on viscosity is lacking. The current study aims to develop a mathematical model for the drainage of Newtonian fluids and also for power-law non-Newtonian fluids of different viscosities.

METHODS

This study is an extension of our previous study on the mathematical model of tear drainage. The tear drainage model is modified to describe the drainage of Newtonian fluids with viscosities higher than the tear viscosity and power-law non-Newtonian fluids with rheological parameters obtained from fitting experimental data in literature. The drainage rate through canaliculi was derived from the modified drainage model and was incorporated into a tear mass balance to calculate the transients of total solute quantity in ocular fluids and the bioavailability of instilled drugs.

RESULTS

For Newtonian fluids, increasing the viscosity does not affect the drainage rate unless the viscosity exceeds a critical value of about 4.4 cp. The viscosity has a maximum impact on drainage rate around a value of about 100 cp. The trends are similar for shear thinning power law fluids. The transients of total solute quantity, and the residence time agrees at least qualitatively with experimental studies.

CONCLUSIONS

A mathematical model has been developed for the drainage of Newtonian fluids and power-law fluids through canaliculi. The model can quantitatively explain different experimental observations on the effect of viscosity on the residence of instilled fluids on the ocular surface. The current study is helpful for understanding the mechanism of fluid drainage from the ocular surface and for improving the design of dry eye treatments.

Low molecular weight hyaluronan shielding of DNA/PEI polyplexes facilitates CD44 receptor mediated uptake in human corneal epithelial cells

AIM

It was the aim of this study to prepare purified DNA/PEI polyplexes, which are coated with hyaluronan to facilitate CD44 receptor mediated uptake of the DNA/PEI polyplex and to reduce unspecific interactions of the complex with negatively charged extracellular matrix components on the ocular surface.

METHODS

Hyaluronans of different molecular weights (<10 kDa, 10-30 kDa and 30-50 kDa) were isolated after enzymatic degradation of high molecular weight hyaluronan via ultrafiltration by centrifugation. The influence of the different hyaluronans used for coating on the stability and transfection efficiency of the complexes was evaluated in vitro. Transfection and uptake studies were performed in human corneal epithelial (HCE) cells. CD44 receptor expression of this cell model was evaluated by immunohistochemistry.

RESULTS

Coating of purified DNA/PEI polyplexes with low molecular weight hyaluronan (<10 kDa) facilitated receptor-mediated uptake via the CD44 receptor in HCE cells, increased complex stability in vitro, and effectively shielded the positive surface charges of the polyplex without decreasing its transfection efficiency. Higher molecular weights and larger amounts of hyaluronan in the complexes resulted in lesser improvements in the stability and transfection efficacy of the complexes.

CONCLUSIONS

Coating of polyplexes with low molecular weight hyaluronan is a promising strategy for gene delivery to the ocular surface, where CD44 receptor mediated uptake decreased cytotoxicity and reduced non-specific interactions with the negatively charged extracellular matrix components are considered beneficial for increased transfection efficiency of non-viral vectors.

Management and Therapy of Dry Eye Disease: Report of the Management and Therapy Subcommittee of the International Dry Eye WorkShop (2007)

The members of the Management and Therapy Subcommittee assessed current dry eye therapies. Each member wrote a succinct evidence-based review on an assigned aspect of the topic, and the final report was written after review by and with consensus of all subcommittee members and the entire Dry Eye WorkShop membership. In addition to its own review of the literature, the Subcommittee reviewed the Dry Eye Preferred Practice Patterns of the American Academy of Ophthalmology and the International Task Force (ITF) Delphi Panel on Dry Eye. The Subcommittee favored the approach taken by the ITF, whose recommended treatments were based on level of disease severity. the recommendations of the Subcommittee are based on a modification of the ITF severity grading scheme, and suggested treatments were chosen from a menu of therapies for which evidence of therapeutic effect had been presented.

Increasing importance of dry eye syndrome and the ideal artificial tear: consensus views from a roundtable discussion

BACKGROUND

Dry eye syndrome is a highly prevalent, yet largely under diagnosed, condition that can substantially affect quality of life. Left untreated, dry eye is associated with chronic eye pain and increased risk of ocular surface disease. Current demographic changes and lifestyle factors indicate that the dry eye syndrome patient population will increase significantly, ensuring that general practitioners and ophthalmic clinicians alike will experience more patients presenting with dry eye symptoms. Greater public and practitioner awareness of emerging research, technologies, and therapies is crucial to ensuring appropriate interventions to meet specific patient needs and result in clinically favorable outcomes.

ROUNDTABLE ASSEMBLY

In August 2005, a team of ocular surface experts convened for a 1-day roundtable session to discuss the latest information on diagnosing and treating dry eye syndrome and real-world issues in artificial tear therapy, including preservative use.

ROUNDTABLE DISCUSSION

The discussion centered on the mild to moderate dry eye patient and critical features of the ideal artificial tear, which are preservative-free formulation, protection from microbial contamination, cost-effective, non-blurring, and easy to use. Products that match this profile have the advantage of being able to benefit the myriad of patients who comprise the dry eye syndrome population. Ocular surface health should always remain a top priority. Preferred Practice Pattern Dry Eye Syndrome Medical Treatment guidelines should be modified to recommend the use of preservative-free formula artificial tear products for all levels of dry eye conditions in consideration of the medical benefit they offer to dry eye syndrome sufferers.

CONCLUSION

The growing prevalence of dry eye syndrome demands increased attention. Further research, enhanced diagnostic tests, increased use of preservative-free artificial tear formulations as first-line therapy, greater patient-practitioner interaction, and patient education are warranted.

Tear clearance measurement in patients with dry eye syndrome using quantitative lacrimal scintigraphy

OBJECTIVE

The aim of this study was to evaluate the tear clearance in patients with dry eye syndrome using quantitative lacrimal scintigraphy.

MATERIALS AND METHODS

We investigated 21 patients (42 eyes; 18 women, 3 men; mean age, 63.19 +/- 13.33 years) with dry eye syndrome. Additionally, for the sake of comparison, 12 normal subjects of the same age group (24 eyes; 10 women, 2 men; mean age, 68.25 +/- 2.63 years) were included. Lacrimal scintigraphy, Schirmer-1 test, BUT, and rose bengal ocular surface vital staining were performed in these cases.

RESULTS

According to the results of lacrimal scintigraphy, the mean value of T 1/2 was 4.16 +/- 1.22 minutes and the mean value of RI was 14.15% +/- 2.30% in normal subjects. However, in patients with dry eye syndrome, these values were 20.59 +/- 1.97 minutes and 55.64% +/- 6.90%, respectively. Consistent with the results of ophthalmologic tests, the mean Schirmer-1 value was 12.46 +/- 2.10 mm, the mean value of BUT was 14.36 +/- 3.40 seconds, and the mean staining value of the rose bengal was 1.98 +/- 0.80 in normal subjects, whereas these values were 1.36 +/- 0.49 mm, 5.46 +/- 1.33 seconds, 6.62 +/- 0.86, respectively, in patients with dry eye syndrome. When we compared the results of lacrimal scintigraphy and the results of ophthalmologic tests, an inverse correlation was noted between both the T1/2 and RI values and both the Schirmer-1 and BUT values in all subjects (p < 0.001). However, there was a greater positive correlation between the rose bengal ocular surface staining value and both the T1/2 and RI values in all cases (p < 0.001).

CONCLUSION

In the current study, it was concluded that although the lacrimal drainage system was normal, tear clearance was significantly delayed in dry eye patients. With this study, we have shown that quantitative lacrimal scintigraphy, which is an objective, practical, and noninvasive method, appears to be useful for the assessment of the tear clearance in patients with dry eye syndrome.

Effects of various lubricants on corneal surface regularity in rabbits

The aim of this study was to establish a method for analysis of tear film stability and thereby to investigate the effects of lubricants on corneal surface regularity and corneal epithelial damage in anesthetized rabbits with the eye held open. Saline-instilled and noninstilled eyes manifested a time-dependent increase in the corneal surface regularity index (SRI). In contrast, 0.1% hyaluronic acid (HA) prevented the increase in the SRI for up to 20 min after instillation. Methylene blue uptake into the damaged cornea was significantly greater in eyes that received saline than in those treated with HA. Whereas eyes instilled with 0.5% methylcellulose (MC) or 0.35% sodium carboxymethylcellulose (CMC) manifested an increase in the SRI similar to that apparent in those that received saline, 1.0% chondroitin sulfate (CS) prevented the increase in the SRI for up to 10 min after instillation. In conclusion, we have established a method for analysis of tear film stability in rabbits. Our results suggest that tear film stability is closely related to corneal surface damage and that topical instillation of 0.1% HA or 1.0% chondroitin sulfate warrants further investigation as a potential treatment for patients with dry eye.

Silicone versus collagen plugs for treating dry eye: results of a prospective randomized trial including lacrimal scintigraphy

PURPOSE

To compare the short-term efficacy of collagen and silicone plugs for treating dry eye using quantitative lacrimal scintigraphy.

DESIGN

Prospective randomized clinical trial.

METHODS

In this institutional study, 24 dry eye patients were evaluated in two groups: group I (n = 22 eyes) received collagen plugs and group II (n = 26 eyes) received silicone plugs. Comparisons were made with normal control subjects (n = 22 eyes). Data for the Schirmer I test, tear break-up time, and ocular surface staining with rose bengal dye were recorded before and after punctal occlusion. Lacrimal scintigraphy was performed at each time point, and the time to half maximum activity on the ocular surface (T(1/2)), and the percentage retention of activity on the ocular surface at the end of the dynamic study (RI) were recorded.

RESULTS

In both patient groups, Schirmer I results, tear break-up times, and rose bengal staining scores improved significantly after plug insertion. Mean T(1/2) values and RI values increased significantly in both groups (P < .0001 for both). The differences for these values between groups I and II was statistically insignificant (P > .05).

CONCLUSIONS

Collagen and silicone plugs both resulted in significant increases in aqueous tear volume, half-life of nuclear material on the ocular surface, and percentage of nuclear material retention. The groups' post-insertion values for all parameters were similar. These results suggest that these two plug types have similar efficacy as treatments for dry eye in the short term. Further studies evaluating long-term results are required.

Ocular Pharmacokinetics and Safety of Ciclosporin, a Novel Topical Treatment for Dry Eye

Ciclosporin is a potent immunomodulator that acts selectively and locally when administered at the ocular surface. 0.05% ciclosporin ophthalmic emulsion has recently been approved by the US FDA for treatment of keratoconjunctivitis sicca (KCS) [dry-eye disease]. After topical application, ciclosporin accumulates at the ocular surface and cornea, achieving concentrations (>/=0.236 microg/g) that are sufficient for immunomodulation. Very little drug penetrates through the ocular surface to intraocular tissues. Ciclosporin is not metabolised in rabbit or dog eyes and may not be prone to metabolism in human eyes. Cultured human corneal endothelial and stromal cells exposed to ciclosporin in vitro exhibited no adverse effects and only minor effects on DNA synthesis. No ocular or systemic toxicity was seen with long-term ocular administration of ciclosporin at concentrations up to 0.4%, given as many as six times daily for 6 months in rabbits and 1 year in dogs. Systemic blood ciclosporin concentration after ocular administration was extremely low or undetectable in rabbits, dogs and humans, obviating concerns about systemic toxicity. In 12-week and 1-year clinical safety studies in dry-eye patients, the most common adverse event associated with the ophthalmic use of ciclosporin emulsion was ocular burning. No serious drug-related adverse events occurred. These data from in vitro, nonclinical and clinical studies indicate effective topical delivery of ciclosporin to desired target tissues along with a favourable safety profile, making 0.05% ciclosporin ophthalmic emulsion a promising treatment for KCS.

Sodium hyaluronate (hyaluronic acid) promotes migration of human corneal epithelial cells in vitro

PURPOSE

Sodium hyaluronate (hyaluronic acid) is known to promote corneal epithelial wound healing in vivo and in vitro, in animal experiments. Sodium hyaluronate is the ligand for CD44, a cell surface adhesion molecule which has been found on normal human corneal epithelial cells. The purpose of this study was to investigate the effect of sodium hyaluronate on human corneal epithelial cell migration, proliferation, and CD44 receptor expression.

METHODS

Human corneal epithelial cell cultures were established from 32 donor corneoscleral rims and maintained separately in three different culture conditions: (1) culture medium only, (2) sodium hyaluronate enriched (0.6 mg/ml) medium, and (3) hydroxypropylmethylcellulose enriched (2.5 mg/ml) medium. The total area of migrating epithelial cell sheets in each case was measured by planimetry on days 4, 8, 12, and 16. Cytospin preparations of cells cultured in the different culture conditions were examined immunohistochemically for proliferation and CD44 receptor expression using antibodies directed against Ki67 and CD44 respectively.

RESULTS

Cells cultured in the presence of sodium hyaluronate showed significantly increased migration at days 12 and 16 (Friedmen test: p = 0.0012, day 16; p = <0.001, day 12) compared with cells cultured in the other media. There was no difference in cell proliferation (Ki67) or CD44 expression on cells cultured in the different culture conditions.

CONCLUSIONS

Sodium hyaluronate promotes migration but not proliferation or CD44 expression on human corneal epithelial cells in vitro. The beneficial effect of sodium hyaluronate in corneal wound healing is likely to be related to rapid migration of cells leading to rapid wound closure. This may be facilitated by the adhesion between CD44 on the cells and hyaluronic acid, which coats the surface of the denuded cornea.

Topical drug delivery in the eye

Introduction of a drug or polymer directly into the conjunctival sac should, in theory, facilitate the maximum level of efficacy. In practice, most material undergoes non-productive loss. The work of David Maurice facilitated a better understanding of drug entry by the study of probes delivered in several formulations, and by the construction of instruments to study probe distribution. This review describes research on the applications of gamma scintigraphy to follow the residence of polymers in the eye and the evaluation of the data to assess potential new materials. Finally, our progress on the construction of an ocular spectrometer to directly follow drug entry following topical administration is described.

Sodium hyaluronate eye drops of different osmolarity for the treatment of dry eye in Sjögren's syndrome patients

AIM

To study the effect of the treatment of dry eye in Sjögren's syndrome patients with hypotonic or isotonic hyaluronate eye drops.

METHODS

40 Sjögren's syndrome patients were divided in two groups and treated as follows: group 1 with hypotonic (150 mOsm/l) 0.4% hyaluronate eye drops; group 2 with isotonic 0.4% hyaluronate eye drops. The eye drops were instilled six times a day for 90 days. Grading of subjective symptoms, break up time (BUT), corneal fluorescein staining, conjunctival rose bengal staining, Schirmer's I test, and conjunctival impression cytology were carried out at 0 and 15, 30, 90 days from the beginning of the study. Patients were examined in a blind fashion. For the statistical analysis the Student's t test, Mann-Whitney U test, and chi(2) test were performed.

RESULTS

Symptoms were statistically significantly improved at day 15 in both groups but group 1 patients had a global score statistically significantly better group 2 (p=0.02). At day 15 group 1 patients had an improvement from baseline values of BUT (p=0.003), fluorescein, and rose bengal score (p=0.000001 and p=0.0004 respectively). Group 2 patients had, at day 15, an improvement of BUT and fluorescein score compared to baseline values (p=0.05 and p=0.0001 respectively). A comparison between the two groups showed better results for group 1 patients at day 15 for rose bengal stain (p=0.01) and for BUT (p=0.05) and fluorescein score (p=0.0003) at day 90. The conjunctival impression cytology showed that group 1 had a statistically significant better total score than group 2 starting from day 15 and lasting throughout the study (p<0.02). Also group 2 patients showed an improvement from baseline values starting from day 30 (p=0.000005).

CONCLUSION

Hyaluronate eye drops are useful for treating severe dry eye in Sjögren's syndrome patients. The use of a formulation with pronounced hypotonicity showed better effects on corneoconjunctival epithelium than the isotonic solution.

Penetration enhancers and ocular bioadhesives: two new avenues for ophthalmic drug delivery

This review is focused on the two avenues of development that promise a major impact on future ocular drug therapeutics: bioadhesives, including hydrogels and other agents like carbopols, polyacrylic acids, chitosan, etc., and penetration enhancers, including different surfactants, calcium chelators, etc. The capacity of some polymers to adhere to the mucin coat covering the conjunctiva and the corneal surface of the eye forms the basis for ocular mucoadhesion. These systems markedly prolong the residence time of a drug in the conjunctival sac, since clearence is now controlled by the much slower rate of mucus turnover rather than the tear turnover rate. But improving the corneal drug retention alone is inadequate in bringing about a significant improvement of drug bioavailability. Another approach consists of transiently increasing the pentration characteristics of the cornea with appropriate substances, known as penetration enhancers or absorption promoters. The main aim of this article is to give an insight into the potential application of mucoadhesives and corneal penetration enhancers for the conception of innovative opthalmic delivery appraoches, to decrease the systemic side effects, and create a more focused effect, which may be achieved with lower doses of the drug. Ophthalmic formulations based on these mucoadhesives and penetration enhancers are simple to manufacture and exhibit an excellent tolerance when administered into the cornea. The use of the former considerably prolongs the corneal contact time and the use of the latter increases the rate and amount of drug transport. The various corneal epithelial barriers along with the major routes of transport of drugs are discussed. The article includes a list of the various substances in use or under investigation for the aforementioned properties, along with their mechanisms of action. A fair appraisal of the subject with regard to these two therapeutic approaches and any expected ill effects has been made.

Enhancement of the mydriatic response to tropicamide by bioadhesive polymers

The aim of this work was to evaluate how the addition of mucoadhesive polymers to aqueous solutions affects the ocular response of tropicamide (0.2%; w/v). The polymer solutions tested were carboxymethylcellulose sodium salt (CMC-Na; 1%; w/v), hyaluronic acid sodium salt (HA-Na; 0.1%; w/v) and polyacrylic acid (PAA; 0.2%; w/v). Polymeric solutions were compared to a nonviscous formulation (AS). In vitro mucoadhesion measurements were expressed as a percentage of the adhesion force mucin-mucin, considering this one as 100% mucoadhesion. The values ofmucoadhesion obtained were 172%, 127%, 103% and 87.6% for formulations with CMC, PAA, HA and AS, respectively. The mydriatic response of tropicamide was determined in adult male New Zealand rabbits, weighing 1.7-2 Kg, by pupil diameter measurements at different times after instillation. The area under the mydriatic response-time curve (AUC 0-6 hr) was interpreted as an indication of the bioavailability of tropicamide in each vehicle. The AUC 0-6 hr was related to the in vitro mucoadhesion for each formulation. Tropicamide solutions with CMC-Na and PAA resulted in mucoadhesion and AUC 0-6 hr values approximately 1.9 and 1.4 times higher than AS. Although the solution with HA-Na was less mucoadhesive than PAA, the hyaluronic acid solution resulted in a higher AUC mydriasis/time value. Formulations with HA-Na and PAA presented values of surface tension close to that observed in the lacrimal fluid, with the Imax (maximum pupil diameter) being higher than for CMC-Na and AS. Greater than 90% of the mydriatic effect disappeared 4.5 hr after instillation for PAA and AS. Nevertheless, the mydriatic effect remained up to 5.5 hr for HA-Na and CMC-Na. HA-Na solution enhanced the bioavailability oftropicamide, presenting a value of mucoadhesion similar to the reference mucin-mucin.

Ocular contact time of a carbomer gel (GelTears) in humans

BACKGROUND/AIMS

Carbomers are widely used in products for the treatment of dry eye; however, the polymer gel thins on addition of probes (for example, fluorescein salt) confounding the comparison of products by objective clinical tests such as spectrophotofluorimetry or scintigraphy. A novel method of radiolabelling carbomer gels, with minimum change to their rheology, has permitted the non-invasive evaluation of precorneal residence of the gel in volunteers using gamma scintigraphy. The technique was used to evaluate the precorneal clearance of the liquid phase and of a suspended particulate in GelTears.

METHODS

Low sodium technetium-99m labelled diethylenetriaminepentacetic acid (99mTc-DTPA) was used to label carbomer 940 gel, either adsorbed onto sterile charcoal to model an entrapped drug, or added directly to the gel to a final activity of 1 MBq per 25 microliters dose. The clearance of the labelled gels was then compared with 99mTc-DTPA labelled saline in 12 volunteers.

RESULTS

The addition of the low sodium radiopharmaceutical produced insignificant rheological changes in the gel compared with conventional 99mTc-DTPA labelling. The residence times on the eye of the gel formulations were significantly greater than that of the saline control. At 8 minutes postdosing, the label levels retained (mean (SD)) on the ocular surface were: saline, 7% (7%); 99mTc-DTPA gel, 42% (27%); and 99mTc-carbon gel, 42% (20%) of administered dose. There was no difference observed in the precorneal distribution between 99mTc-DTPA solution and particulate markers.

CONCLUSIONS

These data demonstrate that carbomer based gels significantly extend contact of solutes or suspended solids with the corneal surface. The method of labelling does not significantly change the initial viscosity and is superior to previous methods which have used sodium salts (for example, sodium fluorescein) and therefore underestimate contact time.

Viscosity-dependent fluid dynamics of eyedrops on the ocular surface

PURPOSE

To determine whether the viscosity of eyedrops affects the distribution of the precorneal tear film.

METHODS

Using a differential pachymetry map, we obtained tear film thickness in healthy volunteers before and after the instillation of nonviscous, aqueous artificial tears and a 0.3% sodium hyaluronate solution.

RESULTS

The instillation of aqueous artificial tears disclosed a significant (P < .05) thickening of the superior corneal tear film compared with the inferior corneal tear film. The increase in thickness by 0.3% sodium hyaluronate solution was uniform, with no differences between the superior and inferior cornea.

CONCLUSIONS

Aqueous artificial tears caused an uneven thickening of the precorneal tear film, with most of the thickening observed at the superior cornea. Lower sections of the cornea may benefit less from the instillation of nonviscous solutions.

Ophthalmic drug delivery systems--recent advances

Eye-drops are the conventional dosage forms that account for 90% of currently accessible ophthalmic formulations. Despite the excellent acceptance by patients, one of the major problems encountered is rapid precorneal drug loss. To improve ocular drug bioavailability, there is a significant effort directed towards new drug delivery systems for ophthalmic administration. This chapter will focus on three representative areas of ophthalmic drug delivery systems: polymeric gels, colloidal systems, cyclodextrins and collagen shields. Hydrogels generally offer a moderate improvement of ocular drug bioavailability with the disadvantage of blurring of vision. In situ activated gel-forming systems are preferred as they can be delivered in drop form with sustained release properties. Colloidal systems including liposomes and nanoparticles have the convenience of a drop, which is able to maintain drug activity at its site of action and is suitable for poorly water-soluble drugs. Among the new therapeutic approaches in ophthalmology, cyclodextrins represent an alternative approach to increase the solubility of the drug in solution and to increase corneal permeability. Finally, collagen shields have been developed as a new continuous-delivery system for drugs that provide high and sustained levels of drugs to the cornea, despite a problem of tolerance. It seems that new tendency of research in ophthalmic drug delivery systems is directed towards a combination of several drug delivery technologies. There is a tendency to develop systems which not only prolong the contact time of the vehicle at the ocular surface, but which at the same time slow down the elimination of the drug. Combination of drug delivery systems could open a new directive for improving results and the therapeutic response of non-efficacious systems.

Ocular drug delivery in veterinary medicine

This paper provides a comprehensive overview of the various approaches currently used in the development of ocular drug delivery systems for the treatment of ocular diseases in animals. It is obvious from the literature that most of the products that are currently available are derived from human medicine without consideration given to the differences which exist between the anatomy and physiology of the eye of various animal species which ultimately affect product design and performance. As a result, many of the products for animal use seem in many circumstances inappropriate for animal care. The article deals with some aspects of eye anatomy and physiology of different animals, and then provides an overview of the most commonly encountered pathologies. The paper then discusses the currently available drug products and finally reviews new delivery concepts. Several hundred references are included in the paper and provide access to further information on the subject.

Gamma scintigraphic comparison of eyedrops containing pilocarpine in healthy volunteers

The aim of the present study was to compare, in healthy human volunteers (male and female), the corneal contact time of various formulations, each containing one viscosity enhancer from the following list: a phase-transition system (gellan gum, Gelrite), a heteropolysaccharide (xanthan gum) and currently used polymers hydroxyethylcellulose, hydroxypropylmethylcellulose, or poly(vinyl alcohol). These different solutions were compared to a reference solution containing no viscosity enhancers. The corneal contact time of the formulations was evaluated over more than 20 minutes by gamma scintigraphy using Technetium-99m (Tc-99m DTPA) as a radioactive label. An eyedrop containing pilocarpine salts (25 microliters) was instilled in one eye only. Each volunteer received 4 formulations, the interval between the instillations being one week. The protocol has been approved by the relevant institutional human experimentation committee. One minute after instillation, only 23% of the reference solution remained on the ocular surface, whereas the novel formulations maintained, respectively, 77% (xanthan gum) or 82% (Gelrite) of the tracer on the ocular surface. Twenty-one min after instillation, 12% (reference solution), 25% (xanthan gum solution), and 39% (gelrite solution) of the tracer remained on the ocular surface. The results confirm that an increase in viscosity of the formulation (xanthan) delays the clearance of the instilled solution by the tear flow. The effect of the gelation mechanism is superior, especially at the later time points. In this respect, xanthan gum and, particularly, Gelrite are suitable vehicles for ophthalmic drugs.

In vivo evaluation of dosage forms: application of gamma scintigraphy to non-enteral routes of administration

The trend to deliver drugs to defined areas of the body involves sophisticated carriers systems. In addition to the in vitro drug release profile one must be aware of the in vivo behaviour of the dosage form and the drug. Gamma scintigraphy is an elegant way to gain insights of the actual in vivo distribution pattern of dosage forms. This technique relies on the use of radioactive tracers included into the medicament and selected so as to enable an optimum detection by a gamma ray camera. The choice of a convenient label enables the in vivo determination of the targeting of the formulation administered through a large number of routes. The present paper reviews applications of gamma scintigraphy for the evaluation of dosage forms administered by the parenteral, rectal, buccal, nasal, pulmonary, and ophthalmic routes.

Sodium hyaluronate 0.25% used as a vehicle increases the bioavailability of topically administered gentamicin

Sodium hyaluronate (SH) solutions have a longer precorneal residence time than isotonic saline solution in rabbits and in humans. The present study investigates the effect of a 0.25% SH vehicle, compared with a phosphate buffer solution (PBS), on the tear concentration after topical administration of gentamicin sulfate (GS) in humans. Eight volunteers received 25 microliters 0.5% GS in PBS in the left eye and 25 microliters 0.5% GS in 0.25% SH in the right eye. Tear samples of 1 microliters were taken from the inferior sulcus using a capillary before instillation and 5, 10, 20, and 40 min after instillation. The tear concentration of GS was determined by radioimmunoassay. There was a statistically significantly higher concentration of GS in the inferior conjunctival sulcus of the SH-instilled eye at 5 min (P < 0.01) and at 10 min (P < 0.05) after instillation (paired t-test, n = 9). At 20 min the concentration of GS in the SH-instilled eye was only slightly higher, and at 40 min GS concentrations in left and right eyes were comparable. SH 0.25% used as a vehicle therefore increases the availability of GS at the ocular surface for at least 10 min. This effect could be due to the prolonged precorneal residence time of SH.

A comparison of the precorneal residence of an artificial tear preparation in patients with keratoconjunctivitis sicca and normal volunteer subjects using gamma scintigraphy

The precorneal residence of an artificial tear preparation has been compared in twelve patients with keratoconjunctivitis sicca (KCS) and twelve normal healthy volunteers. The artificial tear solution was radiolabelled by the inclusion of 1 MBq technetium-99m diethylenetriaminepentaacetic acid (99Tcm-DTPA), and 25 microliters was instilled into one eye only. Deposition of the preparation was followed by gamma scintigraphy. Precorneal clearance of the solution was found to follow bi-exponential kinetics in all subjects with no significant differences in clearance rates between the two study populations. There was also no significant difference in the area under the time-activity profile for the two study groups. This suggests that the reduced reflex tearing and basal lacrimation in KCS patients, indicated by the Schirmer's test, are not important in the clearance of isotonic solutions from the eye surface.