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Use of fluorescent probes to determine MICs of amphotericin B and caspofungin against Candida spp. and Aspergillus spp.

We investigated the utility of mechanism-based fluorescent probes for determination of MICs (FMICs) of amphotericin B and caspofungin against Candida spp. and Aspergillus spp. Amphotericin B was selected as a membrane-active antifungal agent, and caspofungin was selected as a cell wall-active agent. FMICs were also compared to the MIC determined by CLSI (formerly NCCLS) methods. Five isolates per species of Candida albicans, Candida glabrata, Candida parapsilosis, Aspergillus fumigatus, and Aspergillus terreus were studied with either amphotericin B or caspofungin. The fluorescent probes, carboxyfluorescein diacetate (CFDA) for cytoplasmic esterase activity and dihexyloxacarbocyanine iodide (DiOC6) for cell membrane potential, were each added to their respective plates. MICs and FMICs were determined in at least three separate experiments (in duplicate). Fluorescence was measured using a 96-well plate fluorometer. For amphotericin B and caspofungin, the FMIC end point was the lowest concentration of drug at which the percent growth inhibition from treated organisms versus control organisms displayed 80% inhibition for amphotericin B and 50% inhibition for caspofungin as measured by a fluorescent signal. The MIC for amphotericin B was defined as the lowest concentration of antifungal displaying no visible growth for both Aspergillus and Candida spp. The MIC for caspofungin was the lowest concentration of drug that displayed a minimum effective concentration for Aspergillus spp. For Candida spp., the MIC for caspofungin was defined as the concentration at which the antifungal agent significantly inhibits the organism. The FMICs of both antifungals, as measured by the DiOC6 membrane probe, showed good agreement (83% to 100%), within one well dilution, with the MICs against amphotericin B and caspofungin for all species. Also, the FMICs measured by the CFDA cytoplasmic esterase probe reflecting damage due to cell wall or cell membrane showed strong agreement (79 to 100%) with the MICs of both amphotericin B and caspofungin for all species. There was no significant difference in comparisons of MIC and FMIC values (P > or = 0.05). The use of fluorescent probes provides a mechanism-based method of determination of MICs of amphotericin B and caspofungin against Candida spp. and Aspergillus spp. that correlates well with standard methods.

Amphotericin B↗

Caspofungin for invasive candidiasis at a tertiary care medical center.

BACKGROUND: Caspofungin is emerging as first-line therapy for invasive candidiasis. Data on the use of caspofungin for treatment for invasive candidiasis are limited to clinical trials and case reports. We report a single-center experience with 104 consecutive courses of caspofungin for the treatment of invasive candidiasis to evaluate a real-world performance of this drug. METHODS: A retrospective chart review of patients receiving caspofungin at a tertiary care medical center was performed. Patient information and microbiologic data were abstracted from patient charts and electronic medical records. RESULTS: Of 241 patients receiving caspofungin for all indications, 122 (51%) had proven invasive candidiasis. There were 104 treatment courses for candidiasis in 99 patients available for review. Bloodstream (66%) and abdominal infections (25%) were the most common sites of infection. Most infections were non-albicans (80/104, 77%; including patients infected with more than one species). Clinical cure rates at the end of therapy were 83% (57/69) for bloodstream infections and 84% (22/26) for abdominal infections. Caspofungin did not clear candidiasis in 14 episodes (microbiologic cure rate 75%, 42/56). CONCLUSIONS: The clinical use of caspofungin has been successful in the treatment of invasive candidiasis, even in patients with prior antifungal exposure. In this unselected review, caspofungin performed similarly as in clinical trials, and clinicians should consider caspofungin as first-line therapy for invasive candidiasis, particularly non-albicans species.

Antifungal Agents↗

Anti-metabolic activity of caspofungin against Candida albicans and Candida parapsilosis biofilms.

OBJECTIVES: Candidiasis can be associated with the formation of biofilms on bioprosthetic surfaces and the intrinsic resistance of Candida albicans biofilms to the most commonly used antifungal agents has been demonstrated. In this study, we report on the antifungal activity of caspofungin at two different concentrations, on C. albicans and Candida parapsilosis biofilms with different ages of maturation. METHODS: Fifteen strains of C. albicans (10 strains susceptible to fluconazole in vitro and five strains resistant to this antifungal agent) and six strains of C. parapsilosis (all were susceptible to fluconazole in vitro) were studied. The antifungal activity of caspofungin was assessed by looking for a significant inhibition of the metabolic activity of yeasts within biofilms. Biofilms of Candida were produced in vitro, on silicone catheters. RESULTS: Caspofungin used at MIC did not modify the metabolic activity of C. albicans, whatever the maturation age of the biofilms. The same concentration of caspofungin significantly reduced the metabolism (P<or=0.001) of 25% (biofilms of 48 h) to 50% (biofilms of 2 h) of the C. parapsilosis yeasts. The use of a therapeutic concentration of caspofungin (2 mg/L) significantly decreased (P<or=0.001) the metabolism of all the strains of C. albicans and C. parapsilosis tested, independently of the biofilm maturation age. This potent antifungal activity of caspofungin on C. albicans biofilms was observed independently of the yeast susceptibility to fluconazole. CONCLUSIONS: This study demonstrated that caspofungin used at MIC was not sufficient to reduce C. albicans biofilms, but it suggested an activity on C. parapsilosis biofilms depending on their maturation age. This study also indicated that caspofungin used at 2 mg/L could be a good candidate in the prevention of candidiasis associated with silicone medical devices. Our results also suggested that fluconazole resistance of yeasts did not affect caspofungin activity.

Antifungal Agents↗

Caspofungin: antifungal activity in vitro, pharmacokinetics, and effects on fungal load and animal survival in neutropenic rats with invasive pulmonary aspergillosis.

OBJECTIVES: Evaluation of the potential of caspofungin, in relation to pharmacokinetics, in order to optimize its use in the treatment of filamentous fungal infections. METHODS: The in vitro antifungal activity, pharmacokinetics and therapeutic efficacy of caspofungin versus amphotericin B was investigated in vitro as well as in a model of aerogenic Aspergillus fumigatus infection in neutropenic rats, using rat survival and decrease in fungal burden as parameters for therapeutic efficacy. RESULTS: In contrast to amphotericin B, caspofungin shows a concentration-dependent gradual decrease in fungal growth in vitro, which makes it difficult to perform visual readings of antifungal activity (CLSI guidelines). The quantitative XTT [2,3-bis(2-methoxy-4-nitro-5-[(sulphenylamino) carbonyl]-2H-tetrazolium-hydroxide] assay measuring a decrease in fungal metabolic activity seems more appropriate for caspofungin susceptibility testing. Using this assay, in vitro caspofungin was 4-fold less active than amphotericin B. In the infection model, therapy was started 16 h after fungal inoculation, and continued once daily for 10 days. Caspofungin was administered intraperitoneally at 1, 2, 3 or 4 mg/kg/day (CAS 1, 2, 3 or 4), amphotericin B at 1 mg/kg/day (AMB 1). Treatment with CAS 1 or AMB 1 provided modest prolongation of animal survival. The combination of caspofungin and amphotericin B did not show additive effects. Increasing the dosage of caspofungin to 2, 3 or 4 mg/kg/day resulted in a dose-dependent significant increase in efficacy. There was 100% survival among rats in the CAS 4 group, which was correlated with a significant decrease in fungal burden, based on the concentration of A. fumigatus galactomannan in serum and lung tissue and quantification of A. fumigatus DNA in lung tissue. Pharmacokinetic analysis suggested that the CAS 4 dose in rats produced drug exposure comparable to the human situation, visualized by similar 24 h AUC and trough concentrations. CONCLUSIONS: The therapeutic efficacy of caspofungin is superior to amphotericin B, which seemed to be discrepant with their in vitro antifungal activity.

Amphotericin B↗

Potential for interactions between caspofungin and nelfinavir or rifampin.

The potential for interactions between caspofungin and nelfinavir or rifampin was evaluated in two parallel-panel studies. In study A, healthy subjects received a 14-day course of caspofungin alone (50 mg administered intravenously [IV] once daily) (n = 10) or with nelfinavir (1,250 mg administered orally twice daily) (n = 9) or rifampin (600 mg administered orally once daily) (n = 10). In study B, 14 subjects received a 28-day course of rifampin (600 mg administered orally once daily), with caspofungin (50 mg administered IV once daily) coadministered on the last 14 days, and 12 subjects received a 14-day course of caspofungin alone (50 mg administered IV once daily). The coadministration/administration alone geometric mean ratio for the caspofungin area under the time-concentration profile calculated for the 24-h period following dosing [AUC(0-24)] was as follows (values in parentheses are 90% confidence intervals [CIs]): 1.08 (0.93-1.26) for nelfinavir, 1.12 (0.97-1.30) for rifampin (study A), and 1.01 (0.91-1.11) for rifampin (study B). The shape of the caspofungin plasma profile was altered by rifampin, resulting in a 14 to 31% reduction in the trough concentration at 24 h after dosing (C(24h)), consistent with a net induction effect at steady state. Both the AUC and the C(24h) were elevated in the initial days of rifampin coadministration in study A (61 and 170% elevations, respectively, on day 1) but not in study B, consistent with transient net inhibition prior to full induction. The coadministration/administration alone geometric mean ratio for the rifampin AUC(0-24) on day 14 was 1.07 (90% CI, 0.83-1.38). Nelfinavir does not meaningfully alter caspofungin pharmacokinetics. Rifampin both inhibits and induces caspofungin disposition, resulting in a reduced C(24h) at steady state. An increase in the caspofungin dose to 70 mg, administered daily, should be considered when the drug is coadministered with rifampin.

Adult↗

Caspofungin acetate for treatment of invasive fungal infections.

OBJECTIVE: To briefly discuss the changing epidemiology of fungal infections and review currently available agents; provide a review of caspofungin; and discuss its pharmacology, pharmacokinetics, dosing guidelines, safety and efficacy, and role in the treatment of invasive fungal infections as it relates to current antifungal therapy. DATA SOURCES: A MEDLINE (1966 to August 2002) database search using key words caspofungin, echino candins, fungal infections, and invasive aspergillosis, was completed to identify relevant articles including reviews, recent studies, treatment guidelines, and data from Merck and Company. STUDY SELECTION: In vitro studies and all clinical trials were evaluated to summarize the clinical efficacy and safety of caspofungin. DATA SYNTHESIS: The incidence of fungal infections is increasing as the population at risk expands. Cost, resistance, and morbidity and mortality are key issues. Adding to the antifungal armamentarium is necessary to address these therapeutic dilemmas. Caspofungin is the first member of a new class of antifungal agents, the echinocandins, to be approved for clinical use. Caspofungin is classified as a glucan synthase inhibitor and represents a class of agents with a novel mechanism of action. Unlike currently available agents (polyenes, pyrimidines, azoles) that exert their effect on the fungal cell membrane, the echinocandins are the first agents to inhibit fungal cell wall synthesis. Caspofungin exhibits activity against Aspergillus spp. and Candida spp., including non-albicans species. Data from clinical trials demonstrate that caspofungin is effective in patients with invasive aspergillosis as well as candida esophagitis. Its Food and Drug Administration-approved indication is limited to invasive aspergillosis refractory to or intolerant of current therapy. CONCLUSIONS: Caspofungin has activity against Aspergillus spp. as well as a variety of Candida spp. Clinical data support its usefulness in the treatment of invasive aspergillosis and select candida infections. As additional clinical data become available, it seems likely that the therapeutic role of caspofungin will expand.

Anti-Bacterial Agents↗

Caspofungin: first approved agent in a new class of antifungals.

Caspofungin (Cancidas, Merck & Co. Inc.) is the first echinocandin antifungal agent to gain FDA-approval for use in the US. It has excellent clinical activity against Candida spp. and Aspergillus spp. but lacks significant activity against Cryptococcus neoformans. Caspofungin may have some activity against dimorphic fungi such as Histoplasma capsulatum and Coccidioides immitis, but no clinical data is available for treatment of these infections. Caspofungin has demonstrated poor activity against most filamentous fungi in vitro. Several clinical trials have demonstrated its efficacy in the treatment of oropharyngeal, oesophageal and invasive candidiasis, as well as invasive aspergillosis. As a result of caspofungin's unique mechanism of action, and the high morbidity and mortality of invasive fungal infections, there is considerable interest in using this new antifungal agent as part of a combination antifungal therapy. In vitro studies and small case series indicate that caspofungin does not appear to be antagonistic when combined with other antifungals, such as itraconazole, voriconazole or amphotericin B against Aspergillus spp. Caspofungin exerts concentration-dependent killing effects in many different in vitro and animal models of disseminated fungal infection. The usual daily dose is 50 mg/day i.v. following a 70 mg i.v. loading dose. However, higher caspofungin doses have been safely administered and up to 70 mg/day can be administered for patients who fail to respond to lower doses. Caspofungin has an excellent safety profile with reduced toxicities, compared to other licensed antifungal agents. Fever, thrombophlebitis, headache and liver enzyme elevations were the most common drug-related side effects reported in clinical trials so far. Additional data are needed to document its safety in long-term use, and with higher doses in patients with invasive fungal infections. Caspofungin is a promising agent as first-line therapy for invasive candidiasis, and as salvage therapy for invasive aspergillosis. However, more clinical data are needed to define its role as primary therapy for invasive aspergillosis, and its role in combination antifungal therapy.

Adult↗

Assessing the antifungal activity and toxicity profile of amphotericin B lipid complex (ABLC; Abelcet) in combination with caspofungin in experimental systemic aspergillosis.

The purpose of this study was to assess the antifungal activity and renal and hepatic toxicity of amphotericin B lipid complex (ABLC; Abelcet) following co-administration of Caspofungin to rats infected with Aspergillus fumigatus. Aspergillus fumigatus inoculum (1.3-2.3 x 10(7) colony forming units [CFU]) was injected via the jugular vein; 48 h later male albino Sprague-Dawley rats (350-400 g) were administered either a single intravenous (i.v.) dose of Fungizone(R) (1 mg AmpB/kg), ABLC (1 or 5 mg AmpB/kg), or an equivalent volume of normal saline (NS) (vehicle control) once daily for 4 days. Rats were further randomized into groups to receive 3 mg/kg Caspofungin or physiologic saline i.v. once daily for 4 days. To assess antifungal activity, brain, lung, heart, liver, spleen, and kidney sections were homogenized with NS (2 mL; 1 g of each tissue/mL) and a 0.1-mL aliquot was spread plated onto a Sabouraud dextrose agar plate. The plates were incubated for 48 h at 37 degrees C, at which time the numbers of CFU were determined and corrected for tissue weight. To assess renal and hepatic toxicity, serum creatinine and aspartate aminotransferase levels were determined. Fungizone and ABLC at a dosing regimen of 1 mg/kg i.v. once daily for four consecutive days and Caspofungin at a dosing regimen of 3 mg/kg i.v. once daily for four consecutive days had similar effectiveness in decreasing the total number of Aspergillus fumigatus CFUs found in all organs analyzed compared to non-treated controls. A combination of ABLC (1 mg/kg i.v. x 4 days) and Caspofungin (3 mg/kg i.v. x 4 days) significantly decreased the total number of Aspergillus fumigatus CFUs found in all organs analyzed compared to Caspofungin alone and non-treated controls. ABLC at a dosing regiment of 5 mg/kg i.v. once daily for four consecutive days was more effective in decreasing the total number of Aspergillus fumigatus CFUs found in all organs analyzed compared to Fungizone or ABLC alone at 1 mg/kg and Caspofungin alone at 3 mg/kg. However, a combination of ABLC (5 mg/kg i.v. x 4 days) and Caspofungin (3 mg/kg i.v. x 4 days) was not more effective than ABLC at 5 mg/kg or the combination of ABLC at 1 mg/kg and Caspofungin 3 mg/kg in reducing the total number of Aspergillus fumigatus CFUs compared to controls. Except for non-treated infected control rats, none of the treatment groups tested displayed a greater than 50% increase in serum creatinine concentrations from baseline. In addition, only ABLC at a dosing regimen of 1 mg/kg i.v. once daily for four consecutive days displayed a greater than 50% increase in AST concentration from baseline. Taken together, these findings suggest that ABLC at 5 mg/kg once daily x 4 days appears to be the best therapeutic choice in this animal model.

Amphotericin B↗

Caspofungin: the first in a new class of antifungal agents.

Caspofungin is the first approved agent from a new class of antifungals, the echinocandins. By targeting the fungal cell wall (as opposed to the fungal cell membrane), the echinocandins exhibit a unique mechanism of action relative to the other currently approved antifungal agents. Preclinical (in vitro and in vivo) studies have demonstrated activity for caspofungin against the most commonly encountered fungi in the hospital setting, namely Candida and Aspergillus species. Caspofungin is administered as a once-a-day, intravenous formulation. Notably, caspofungin is neither an inhibitor, inducer, nor metabolite of the cytochrome p450 system. To date, few drug-drug interactions have been seen for this echinocandin. A number of Phase II and III clinical studies in documented invasive candidiasis, esophageal candidiasis, and invasive aspergillosis have been completed and have demonstrated efficacy for caspofungin against all three diseases. In all studies, caspofungin manifested an excellent safety profile with few serious, drug-related adverse events or discontinuations due to drug-related adverse events. Isolated symptoms compatible with histamine release have been infrequently reported. In clinical studies, drug-related nephrotoxicity with caspofungin has been rare, and the incidence of liver transaminase elevations has been similar to the incidence seen with comparator agents. Results from a Phase III study as empirical therapy in patients with febrile neutropenia are anticipated in late 2003. Overall, caspofungin represents an important addition to the current antifungal armamentarium.

Animals↗

Efficacy of Abelcet and caspofungin, alone or in combination, against CNS aspergillosis in a murine model.

OBJECTIVES: Currently, few options exist to treat central nervous system (CNS) aspergillosis, which is usually fatal. We tested the efficacy of Abelcet and caspofungin, alone and in combination for treatment of this disease. METHODS: Male CD-1 mice were immunosuppressed with 200 mg/kg cyclophosphamide 2 days prior to infection and every 5 days thereafter. In the first study, mice were infected intracerebrally with 2.1 x 10(6) conidia/mouse of Aspergillus fumigatus; 10 days of once daily therapy began one day later. Groups of 10 received 0.8, 4, or 8 mg/kg of Abelcet, intravenously (iv), or caspofungin, intraperitoneally, 0.8 mg/kg of conventional amphotericin B (AmB) iv, or no treatment. In a second study, mice were challenged with 6.4 x 10(6) conidia and given no treatment, 8 mg/kg of Abelcet or caspofungin, alone or in combination. On day 14, cfu were determined in survivors by plating of organ homogenates. RESULTS: In the first study, mice given any regimen of Abelcet or caspofungin had a survival rate > or =80% whereas untreated had 90% mortality. All drug regimens prolonged survival (P < or = 0.0008) and reduced cfu (P < or = 0.0001-0.003) recovered from the brains and kidneys compared with untreated. Abelcet showed an apparent dose-related reduction of cfu in the brains. Abelcet at 4 or 8 mg/kg were equivalent to AmB in reducing cfu from both organs (P > 0.05); AmB was superior to 0.8 mg/kg of Abelcet in the brain only (P < 0.02). Abelcet at 8 mg/kg or AmB at 0.8 mg/kg were superior to all regimens of caspofungin in reducing cfu (P < or = 0.05-0.001). In the second study, Abelcet alone significantly prolonged survival and reduced cfu in the organs versus the controls. Caspofungin did not significantly prolong survival or reduce cfu in comparison with the controls. In combination, Abelcet and caspofungin were equivalent to Abelcet alone. CONCLUSIONS: Abelcet proved to be efficacious, but not curative, in the treatment of CNS aspergillosis and was equivalent overall to conventional AmB. Caspofungin was not as effective against the larger inoculum, but did not enhance or interfere with the efficacy of Abelcet. Since Abelcet displayed dose-responsive efficacy, it is possible higher doses could produce superior results, yet not show toxicity.

Amphotericin B↗

An open study of the comparative efficacy and safety of caspofungin and liposomal amphotericin B in treating invasive fungal infections or febrile neutropenia in patients with haematological malignancy.

In a clinical non-trial setting, the efficacy and safety of caspofungin was compared with liposomal amphotericin B for the management of febrile neutropenia or invasive fungal infections in 73 episodes in patients with haematological malignancy. There were fewer episodes of drug toxicity with caspofungin than liposomal amphotericin B (58.3 vs 83.7 %, P=0.02). The favourable response rate for episodes of febrile neutropenia treated with caspofungin or liposomal amphotericin B was similar at 37.5 and 53.8 %, respectively, but more breakthrough fungal infections occurred with caspofungin than with liposomal amphotericin B (33.3 vs 0 %, P<0.05) in these patients who did not receive antifungal prophylaxis. None of four episodes of candidaemia or hepatosplenic candidiasis responded to caspofungin compared with three of four episodes treated with liposomal amphotericin B. Mortality was significantly higher with caspofungin treatment compared with liposomal amphotericin B (6/24 vs 2/49, P=0.01), mainly due to an excess of fungal infections (P=0.04). Caspofungin treatment was a significant independent predictor of mortality [odds ratio=7.6 (95 % confidence interval 1.2-45.5)] when sepsis severity, prolonged neutropenia and length of antifungal therapy were considered in a multiple logistic regression model. In clinical practice, there is a suggestion that caspofungin may not be as effective as liposomal amphotericin B in preventing breakthrough invasive fungal infections in febrile neutropenia or in preventing fungus-related deaths. Because of the potential biases in this observational study, these preliminary findings should be interpreted with caution and clarified with a larger cohort of patients.

Adult↗

Influence of human sera on the in vitro activity of the echinocandin caspofungin (MK-0991) against Aspergillus fumigatus.

There have been several reports that the activity of echinocandin antifungal agents is not affected or decreased in the presence of human sera. It is known that these drugs are bound >80% in animal and human sera. The activity of the echinocandin caspofungin (MK-0991), a 1,3-beta-D-glucan synthase inhibitor, against Aspergillus fumigatus with and without human sera was studied. Conidia of A. fumigatus in microtest plate wells formed germlings after overnight culture in RPMI 1640. Caspofungin was then added with or without serum, and the germlings were incubated at 37 degrees C for 24 h. Human serum (5%) in RPMI 1640 alone did not significantly inhibit the growth of A. fumigatus in vitro. Caspofungin in RPMI 1640 exhibited dose-dependent inhibition, with concentrations of 0.1 and 0.05 microg/ml inhibiting 24.9% +/- 10.4% and 11.7% +/- 3.6%, respectively (n = 10; P < 0.01). The addition of 5% human serum to caspofungin at 0.1 or 0.05 microg/ml increased the inhibition to 78.6% +/- 5.8% or 58.3% +/- 19.2%, respectively (n = 10; P < 0.01 versus controls and versus the drug without serum). Lower concentrations of serum also potentiated drug activity. The effect of human sera was further seen when using caspofungin that had lost activity (e.g., by storage) against A. fumigatus at 0.1 microg/ml. Inactive caspofungin alone demonstrated no significant inhibition of hyphal growth, whereas the addition of 5% human serum to the inactive drug showed 83% +/- 16.5% inhibition (n = 5; P < 0. 01). The restoration of activity of caspofungin was seen at concentrations as low as 0.05% human serum. In contrast to prior reports, this study suggests that human serum acts synergistically with caspofungin to enhance its inhibitory activity in vitro against A. fumigatus.

Anti-Bacterial Agents↗

Comparison of the echinocandin caspofungin with amphotericin B for treatment of histoplasmosis following pulmonary challenge in a murine model.

Twenty clinical isolates of Histoplasma capsulatum were tested for their in vitro susceptibilities to caspofungin in comparison to those to amphotericin B by following National Committee for Clinical Laboratory Standards guidelines for yeasts. The mean MICs were 16.6 microgram/ml (range, 8 to 32 microgram/ml) for caspofungin and 0.56 microgram/ml (range, 0.5 to 1.0 microgram/ml) for amphotericin B. Survival experiments used a 10(5) dose in a pulmonary challenge model with B6C3F(1) mice. All mice that received amphotericin B at 2 mg/kg of body weight every other day (q.o.d.), 30% of mice that received caspofungin at 8 mg/kg/day, and 20% of mice that received caspofungin at 4 mg/kg/day survived to day 15, while mice that received caspofungin at 2 mg/kg/day and all control mice that received the vehicle died by day 14. Amphotericin B at 2 mg/kg q.o.d. markedly reduced the fungal burden in the lungs and spleens, as measured by Histoplasma antigen detection techniques and quantitative cultures, for each comparison. Caspofungin at 10 mg/kg twice a day (b.i.d.) did not reduce the fungal burden, as measured by antigen detection techniques, but slightly reduced the levels of fungi in both the lungs and spleens, as determined by quantitative cultures. Caspofungin at 5 mg/kg b.i.d. did not affect fungal burden. Overall, caspofungin had only a slight effect on survival or fungal burden.

Amphotericin B↗

Disposition of caspofungin, a novel antifungal agent, in mice, rats, rabbits, and monkeys.

The metabolism, excretion, and pharmacokinetics of caspofungin (Cancidas; Merck & Co., Inc.) were investigated after administration of a single intravenous dose to mice, rats, rabbits, and monkeys. Caspofungin had a low plasma clearance (0.29 to 1.05 ml/min/kg) and a long terminal elimination half-life (11.7 h to 59.7 h) in all preclinical species. The elimination kinetics of caspofungin were multiphasic and displayed an initial distribution phase followed by a dominant beta-elimination phase. The presence of low levels of prolonged radioactivity in plasma was observed and was partially attributable to the chemical degradation product M0. Excretion studies with [(3)H]caspofungin indicated that the hepatic and renal routes play an important role in the elimination of caspofungin, as a large percentage of the radiolabeled dose was recovered in urine and feces. Excretion of radioactivity in all species studied was slow, and low levels of radioactivity were detected in daily urine and fecal samples throughout a prolonged collection period. Although urinary profiles indicated the presence of several metabolites (M0, M1, M2, M3, M4, M5, and M6), the majority of the total radioactivity was associated with the polar metabolites M1 [4(S)-hydroxy-4-(4-hydroxyphenyl)-L-threonine] and M2 [N-acetyl-4(S)-hydroxy-4-(4-hydroxyphenyl)-L-threonine]. Caspofungin was thus primarily eliminated by metabolic transformation; however, the rate of metabolism was slow. These results suggest that distribution plays a prominent role in determining the plasma pharmacokinetics and disposition of caspofungin, as very little excretion or biotransformation occurred during the early days after dose administration, a period during which concentrations in plasma fell substantially. The disposition of caspofungin in preclinical species was similar to that reported previously in humans.

Animals↗

Pharmacokinetics, safety, and tolerability of caspofungin in children and adolescents.

Caspofungin is a parenteral antifungal that inhibits beta-1,3-D-glucan synthesis. Although licensed for adult use, the appropriate caspofungin dosing regimen in pediatric patients is not yet known. We therefore investigated the pharmacokinetics and safety of caspofungin in pediatric patients. Thirty-nine children (ages 2 to 11 years) and adolescents (ages 12 to 17 years) with neutropenia were administered caspofungin using either a weight-based regimen (1 mg/kg of body weight/day) or a body surface area regimen (50 mg/m2/day or 70 mg/m2/day). Plasma samples for caspofungin profiles were collected on days 1 and 4. These results were compared to those from adults treated with either 50 or 70 mg/day for mucosal candidiasis. In children receiving 1 mg/kg/day (maximum, 50 mg/day), the area under the concentration-time curve over 24 h (AUC(0-24)) was significantly smaller (46% after multiple doses) than that observed in adults receiving 50 mg/day (P < 0.001). In children and adolescents receiving 50 mg/m2/day (maximum, 70 mg/day), the AUC(0-24) following multiple doses was similar to that for the exposure in adults receiving 50 mg/day. The AUC(0-24) and concentration trough (at 24 h) in pediatric patients receiving the 50-mg/m2 daily regimen were consistent across the range of ages. Caspofungin was generally well tolerated in this study. None of the patients developed a serious drug-related adverse event or were discontinued for toxicity. These results demonstrate that caspofungin at 1 mg/kg/day in pediatric patients is suboptimal. Caspofungin administration at 50 mg/m2/day provides a comparable exposure to that of adult patients treated with 50 mg/day.

Adolescent↗

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.

Administration, Topical↗

Caspofungin susceptibility testing of isolates from patients with esophageal candidiasis or invasive candidiasis: relationship of MIC to treatment outcome.

The caspofungin clinical trial database offers an opportunity to assess susceptibility results for Candida pathogens obtained from patients with candidiasis and allows for correlations between efficacy outcomes and MICs. Candida isolates have been identified from patients enrolled in four studies of esophageal candidiasis and two studies of invasive candidiasis. The MICs of caspofungin for all baseline isolates were measured at a central laboratory using NCCLS criteria (document M-27A); MICs for caspofungin were defined as the lowest concentration inhibiting prominent growth at 24 h. MICs were then compared to clinical and microbiological outcomes across the two diseases. Susceptibility testing for caspofungin was performed on 515 unique baseline isolates of Candida spp. obtained from patients with esophageal candidiasis. MICs for caspofungin ranged from 0.008 to 4 microg/ml; the MIC50 and MIC90 were 0.5 and 1.0 microg/ml, respectively. Susceptibility testing was also performed on 231 unique baseline isolates of Candida spp. from patients with invasive candidiasis. The majority (approximately 96%) of MICs were between 0.125 and 2 microg/ml, with MIC50 and MIC90 for caspofungin being 0.5 and 2.0 microg/ml, respectively. Overall, caspofungin demonstrated potent in vitro activity against clinical isolates of Candida species. A relationship between MIC for caspofungin and treatment outcome was not seen for patients with either esophageal candidiasis or invasive candidiasis. Patients with isolates for which the MICs were highest (>2 microg/ml) had better outcomes than patients with isolates for which the MICs were lower (<1 microg/ml). Additionally, no correlation between MIC and outcome was identified for specific Candida species.

Antifungal Agents↗

In vitro susceptibilities of Candida spp. to caspofungin: four years of global surveillance.

Caspofungin is being used increasingly as therapy for invasive candidiasis. Prospective sentinel surveillance for emergence of in vitro resistance to caspofungin among invasive Candida spp. isolates is indicated. We determined the in vitro activity of caspofungin against 8,197 invasive (bloodstream or sterile-site) unique patient isolates of Candida collected from 91 medical centers worldwide from 1 January 2001 to 31 December 2004. We performed antifungal susceptibility testing according to the Clinical and Laboratory Standards Institute (CLSI, formerly NCCLS) M27-A2 method and used a 24-h prominent inhibition endpoint for determination of the MIC. Of 8,197 invasive Candida spp. isolates, species distribution was as follows: 54% Candida albicans, 14% C. glabrata, 14% C. parapsilosis, 11% C. tropicalis, 3% C. krusei, and 4% other Candida spp. Overall, caspofungin was very active against Candida (MIC50/MIC90, 0.03/0.25 microg/ml; 98.2% were inhibited at a MIC of < or = 0.5 microg/ml and 99.7% were inhibited at a MIC of < or = 1 microg/ml). Results by species (expressed as MIC50/MIC90 and the percentage inhibited at < or = 1 microg/ml) were as follows: C. albicans, 0.03/0.06, 99.9; C. glabrata, 0.03/0.06, 99.9; C. parapsilosis, 0.5/0.5, 99.0; C. tropicalis, 0.03/0.06, 99.7; C. krusei, 0.12/0.5, 99.0; and C. guilliermondii, 0.5/1, 94.4. Of the 25 isolates with caspofungin MICs of >1 microg/ml, 12 isolates were C. parapsilosis, 6 isolates were C. guilliermondii, 2 isolates were C. rugosa, and 1 isolate each was C. albicans, C. glabrata, C. krusei, C. lusitaniae, and C. tropicalis. There was no significant change in caspofungin activity over the 4-year study period. Likewise, there was no difference in activity by geographic region. Caspofungin has excellent in vitro activity against invasive clinical isolates of Candida from centers worldwide. Our prospective sentinel surveillance reveals no evidence of emerging caspofungin resistance among invasive clinical isolates of Candida.

Antifungal Agents↗