Bioavailability and penetration of topical amphotericin B in the anterior segment of the rabbit eye

Rifampin Enhances the Activity of Amphotericin B against Fusarium solani Species Complex and Aspergillus flavus Species Complex Isolates from Keratitis Patients

The in vitro activities of amphotericin B in combination with rifampin were assessed against 95 ocular fungal isolates. The interactions between amphotericin B and rifampin at 4, 8, 16, and 32 μg/ml were synergistic for 11.8%, 51.0%, 90.2%, and 94.1%, respectively, of Fusarium solani species complex isolates and for 13.6%, 45.5%, 93.2%, and 95.5%, respectively, of Aspergillus flavus species complex isolates. Antagonism was never observed for the amphotericin B-rifampin combinations.

Efficacy Profile of Intracameral Amphotericin B. The Often Forgotten Step

PURPOSE

The objectives of this study were to assess visual and structural outcomes in mycotic keratitis after conventional treatment (topical and systemic antifungals) and intracameral amphotericin B (ICAMB), and to evaluate any complications.

DESIGN

This was a prospective, nonrandomized, nonblinded interventional study.

METHODS

This study was conducted on 104 eyes of 104 patients with fungal corneal ulcers. Patients were categorized into 2 groups: group A, who received conventional topical and systemic antifungal medications, and group B, who received ICAMB in the dose of 5 to 10 μg in 1 mL of 5% dextrose. Response to treatment was evaluated. Results of the 2 groups were compared with appropriate statistical indices.

RESULTS

The mean final visual acuity in patients in group B receiving ICAMB was 1.22 ± 0.31 logMAR units. The improvement in mean visual acuity was 1.40 ± 0.2 logMAR units. In group A, mean visual outcome was 1.25 ± 0.73 logMAR units. There was an improvement by 0.55 ± 0.30 logMAR units. Healing with varying degrees of opacification occurred in a significant number of patients (81.48%) treated with ICAMB as compared with conventional treatment (Z = 2.24, P < 0.05). Complications, such as sloughing, occurred in significantly fewer patients treated with ICAMB as compared with conventional treatment (Z = 2.29, P < 0.05).

CONCLUSIONS

In cases of keratomycosis where response to local and systemic antifungal treatment is not evident after 7 days, ICAMB can be safely administered to prevent the progression of ulcers and the development of complications.

Voriconazole concentration in human aqueous humor and plasma during topical or combined topical and systemic administration for fungal keratitis

Voriconazole (VRC) is an antifungal drug that effectively treats keratitis caused by yeasts and molds when administered orally. We retrospectively evaluated clinical outcomes and plasma and aqueous humor drug concentrations in five patients with fungal keratitis and one patient with posttraumatic endophthalmitis who were treated with VRC. VRC was administered either topically (1% eye drops every hour) or orally (400 mg twice a day). Plasma and aqueous humor samples from affected eyes were taken 12 h after oral administration or 1 h after eye drop application. The drug concentration was measured by liquid chromatography with UV or mass spectrometric detection. All six patients responded well to VRC treatment. The VRC concentration ranged from 2.93 to 3.40 mg/liter in the aqueous humor and from 3.20 to 4.20 mg/liter in the plasma after combined oral and topical treatment. Topical administration alone resulted in highly variable trough VRC concentrations of 0.61 to 3.30 mg/liter in the aqueous humor. VRC concentrations were above the MIC for Candida albicans Aspergillus fumigatus and clinical improvement was seen in all four patients with C. albicans and A. fumigatus keratitis. Combined orally and topically administered VRC resulted in aqueous humor drug concentrations of > or =2.93 mg/liter, which is above the VRC MIC for most fungi. Topical VRC treatment resulted in an aqueous humor drug concentration >0.61 mg/liter, which is above the MIC for most Candida species. The results from this small series of patients suggest that both topical and combined systemic and topical VRC therapy can be effective in treating fungal keratitis. Furthermore, the data provide preliminary support for initiation of VRC treatment with a combined topical and systemic administration until the causative fungus and its MIC are identified.

Topical caspofungin for treatment of keratitis caused by Candida albicans in a rabbit model

Candida albicans is the most frequent cause of fungal keratitis in temperate regions. Caspofungin has potent activity against Candida spp. in a variety of clinical settings. Little is known, however, about its activity against fungal keratitis. We compared the efficacy of topical caspofungin with that of topical amphotericin B (AMB) in a rabbit model of experimental keratomycosis. Keratitis was induced with a standardized inoculum of Candida albicans (SC 5314) placed on the debrided cornea. Twenty-four hours after infection, animals were randomly assigned to treatment with 0.15% caspofungin, 0.5% caspofungin, 0.15% AMB, and a saline control (n = 12 rabbits in each group). For the first 12 h, treatment was repeated every 30 min and, after a 12-h pause, was resumed at hourly intervals for another 12 h. The animals were examined and killed 12 h after administration of the last dose. Treatment effects were evaluated by clinical assessment, fungal culture, and histopathology. Drug treatment significantly reduced corneal fungal recovery from 3.78 log10 CFU in saline-treated animals to 2.97, 1.76, and 1.18 log10 CFU in animals treated with 0.15% caspofungin, 0.5% caspofungin, and 0.15% AMB, respectively. By histopathology, the mean hyphal density was significantly lower in the corneas of treated animals than in those of the controls; there was no difference in hyphal densities between the different treatment groups. The depth of corneal invasion was not significantly reduced by the antifungal treatments. By clinical assessment, keratitis progressed in animals treated with saline, whereas disease progression was inhibited by all drug treatment regimens. In our rabbit model, 0.5% caspofungin was as effective as 0.15% AMB for the topical treatment of Candida keratitis. The potential clinical efficacy of caspofungin awaits further investigation.

Intracameral amphotericin B: initial experience in severe keratomycosis

PURPOSE

Fungal keratitis is a significant cause of ocular morbidity in India. The most commonly implicated fungi are Aspergillus spp. Patients often present with hypopyon, which usually contains fungal elements. The treatment is difficult owing to poor intraocular penetration of most available antifungal agents. This study evaluated the results of intracameral injection of amphotericin B in natamycin resistant cases of severe keratomycosis.

METHODS

Three patients of culture proven Aspergillus flavus corneal ulcer with hypopyon not responding to topical natamycin 5%, amphotericin B 0.15%, and oral itraconazole were administered intracameral amphotericin B. The first case received 7.5 microg in 0.1 mL followed by two subsequent injections of 10 microg in 0.1 mL each, the second case received two injections of 10 microg in 0.1 mL, and the third patient received a single dose of 10 microg in 0.1 mL. Culture of the aqueous sample also grew A. flavus in all three cases.

RESULTS

All three cases responded favorably, with the ulcer and hypopyon clearing completely. There was no clinical evidence of corneal or lenticular toxicity in any patient.

CONCLUSIONS

Intracameral amphotericin B may be a useful modality in the treatment of severe keratomycosis not responding to topical natamycin. It ensures adequate drug delivery into the anterior chamber and may be especially useful to avoid surgical intervention in the acute stage of the disease.

Advances in the management of keratomycosis and Acanthamoeba keratitis

PURPOSE

In the late 1960s, the management of fungal keratitis was a serious unresolved problem. Little was known of the epidemiology of the disease, and there were no antifungal agents formulated for use in the eye.

METHODS

A thorough review of the literature was done back to 1969 on clinical reports and experimental studies for keratomycosis and Acanthamoeba keratitis.

RESULTS

Since 1969, through basic and clinical research, the epidemiology of the disease worldwide is better understood. One new topical antifungal agent, natamycin, with efficacy against filamentous fungi has been developed and the pharmacokinetics of topically applied antifungal drops have been explored. Progress has been slow but the prognosis for keratomycosis has immeasurably improved over the period. Acanthamoeba was first recognized as an ocular pathogen in 1973 and was the cause of an epidemic in the 1980s caused by contaminated contact lens, although other risk factors were also identified. At the onset of the epidemic, there was no known treatment. but as a result of intense research efforts, within a few years a well-defined therapeutic approach had been developed that had a significant impact on the prognosis for this initially devastating infection. For both infections, the role of corticosteroids for controlling the inflammation remains controversial, but the place for keratoplasty is now well defined.

CONCLUSIONS

Although there has been steady progress in the management of both infections, continued research is the way to define more effective medical and surgical therapy.

An evaluation of intrastromal injection of antifungal agents

The effect of the intrastromal injection of a mixture of amphotericin B, miconazole, natamycin, and nystatin and the component agents alone was studied in Dutch-belted rabbits by standard bioassay. Twenty-four hours following injection, the inhibiting effect of the mixture was equivalent to that of nystatin alone. All other agents exhibited inferior activity. The intrastromal injection of this mixture appears to offer no therapeutic advantage.

Collagen shield delivery of amphotericin B

By using a high-pressure liquid chromatography assay, we investigated the ability of collagen shield therapeutic contact lenses to release amphotericin B and deliver it to the anterior segment of rabbit eyes. In vitro studies showed that presoaked collagen shields released most of the amphotericin B within the first hour of elution. We compared the corneal and aqueous humor amphotericin B levels produced by collagen shields soaked in amphotericin B and frequent-drop therapy at four time points over a six-hour period. The collagen shields soaked in amphotericin B produced corneal levels that were higher than those produced by frequent-drop therapy at one hour, equivalent to drop therapy at two and three hours, and lower than drop therapy at six hours. There were no differences in amphotericin B levels in aqueous humor at any time point between rabbits treated with collagen shield delivery and rabbits treated with frequent-drop delivery. The results of this study suggest that amphotericin B delivery to the cornea by collagen shields is comparable to frequent-drop delivery but has the potential benefit of added convenience and compliance.

In vitro study of aldose reductase inhibitor concentrations in the lens and inhibitory effect on sugar alcohol accumulation

Rat lenses were cultured in a medium containing either 30mM xylose or 30mM glucose. Inhibitory effects of two aldose reductase inhibitors, AD-5467 and CT-112, on the accumulation of sugar alcohols and the concentrations of the drugs in the lens were measured. Inhibitory effect of lens opacification by the drugs were also observed. Lens opacification was apparently inhibited in a medium containing each of the drugs. Inhibition rates for sugar alcohol accumulation by AD-5467 and CT-112 were unrelated to the kinds of added sugars. 50% inhibition-concentration in the medium was 0.82-1.02 x 10(-7) M for AD-5467 and 3.78-5.92 x 10(-7) M for CT-112, and the resulting concentration of drug in the lens was 2.33-3.08 nmole/g lens for AD-5467 vs. 21.19-24.63 nmole/g lens for CT-112. The results above indicated that the concentration of CT-112 should be 4.6-5.8 times of that of AD-5467 in the medium to attain the same inhibitory effect on sugar alcohol accumulation, and 8.0-9.1 times more CT-112 is needed in the lens. A linear correlation was found on a bilogarithmic graph of concentrations in the medium and in the lens for both drugs. This correlation is an empirical adsorption isotherm shown by Freundrich. So this suggested that both drugs were adsorbed into the lens. The rate of adsorption varied with the drugs. Even when the drug concentrations in the medium were the same, the concentration of CT-112 in the lens was 2-4 times higher than that of AD-5467.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurements of antifungal levels in corneal tissue: a simplified bioassay for amphotericin B

Measuring precise antifungal levels in the cornea with broth-dilution bioassays is difficult, as standard techniques involving visual determination of endpoints are hindered by corneal debris. To increase the precision of the measurement, we modified the sample preparation for bioassay of rabbit corneas treated with subconjunctival amphotericin B. Endpoint determination and variance were compared for a freshly thawed corneal suspension and the supernatant after 24 h equilibration; bioassay of the corneal suspension after 24 h equilibration served as an additional control. All endpoints were read visually in a masked fashion and were verified by culture. The three methods gave comparable endpoint values with equivalent degrees of variance. Amphotericin B levels were consistent by both visual and culture determination; however, endpoints were clearly visible and easier to read for the supernatant. Visual determination of the endpoints for the supernatant following 24 h equilibration simplified and ensured the precision of the bioassay technique.

Pharmacologic management of keratomycoses

Fungal corneal infections can be very difficult to treat. An evolving understanding of the pharmacology of the currently available antifungal agents has led to improved medical treatment of the keratomycoses. The pharmacology, pharmacokinetics, spectrum of activity and toxicity of these agents is reviewed and promising new antifungal compounds and modes of treatment are discussed.