Mechanism of Action
Caspofungin, an echinocandin, inhibits the synthesis of beta (1,3)-D-glucan, an essential component of the cell wall of susceptible Aspergillus species and Candida species. Beta (1,3)-D-glucan is not present in mammalian cells. Caspofungin has shown activity against Candida species and in regions of active cell growth of the hyphae of Aspergillus fumigatus.
There have been reports of clinical failures in patients receiving caspofungin therapy due to the development of drug resistant Candida or Aspergillus species. Some of these reports have identified specific mutations in the Fks subunits, encoded by the fks1 and/or fks2 genes, of the glucan synthase enzyme. These mutations are associated with higher MICs and breakthrough infection. Candida species that exhibit reduced susceptibility to caspofungin as a result of an increase in the chitin content of the fungal cell wall have also been identified, although the significance of this phenomenon in vivo is not well known.
Interaction With Other Antimicrobials
Studies in vitro and in vivo of caspofungin, in combination with amphotericin B, suggest no antagonism of antifungal activity against either A. fumigatus or C. albicans. The clinical significance of these results is unknown.
Caspofungin has been shown to be active against most strains of the following microorganisms both in vitro and in clinical infections [see Indications and Usage (1)]:
Susceptibility TestingFor specific information regarding susceptibility test interpretive criteria and associated test methods and quality control standards recognized by FDA for caspofungin, please see: https://www.fda.gov/STIC.
No long-term studies in animals have been performed to evaluate the carcinogenic potential of caspofungin.
Caspofungin did not show evidence of mutagenic or genotoxic potential when evaluated in the following in vitro assays: bacterial (Ames) and mammalian cell (V79 Chinese hamster lung fibroblasts) mutagenesis assays, the alkaline elution/rat hepatocyte DNA strand break test, and the chromosome aberration assay in Chinese hamster ovary cells. Caspofungin was not genotoxic when assessed in the mouse bone marrow chromosomal test at doses up to 12.5 mg/kg (equivalent to a human dose of 1 mg/kg based on body surface area comparisons), administered intravenously.
Fertility and reproductive performance were not affected by the intravenous administration of caspofungin to rats at doses up to 5 mg/kg. At 5 mg/kg exposures were similar to those seen in patients treated with the 70 mg dose.
In one 5-week study in monkeys at doses which produced exposures approximately 4 to 6 times those seen in adult patients treated with a 70 mg dose, scattered small foci of subcapsular necrosis were observed microscopically in the livers of some animals (2/8 monkeys at 5 mg/kg and 4/8 monkeys at 8 mg/kg); however, this histopathological finding was not seen in another study of 27 weeks duration at similar doses.
No treatment-related findings were seen in a 5-week study in infant monkeys at doses which produced exposures approximately 3 times those achieved in pediatric patients receiving a maintenance dose of 50 mg/m2 daily.
A double-blind study enrolled 1111 febrile, neutropenic (<500 cells/mm3) patients who were randomized to treatment with daily doses of caspofungin (50 mg/day following a 70 mg loading dose on Day 1) or AmBisome (3 mg/kg/day). Patients were stratified based on risk category (high-risk patients had undergone allogeneic stem cell transplantation or had relapsed acute leukemia) and on receipt of prior antifungal prophylaxis. Twenty-four percent of patients were high risk and 56% had received prior antifungal prophylaxis. Patients who remained febrile or clinically deteriorated following 5 days of therapy could receive 70 mg/day of caspofungin or 5 mg/kg/day of AmBisome. Treatment was continued to resolution of neutropenia (but not beyond 28 days unless a fungal infection was documented).
An overall favorable response required meeting each of the following criteria: no documented breakthrough fungal infections up to 7 days after completion of treatment, survival for 7 days after completion of study therapy, no discontinuation of the study drug because of drug-related toxicity or lack of efficacy, resolution of fever during the period of neutropenia, and successful treatment of any documented baseline fungal infection.
Based on the composite response rates, caspofungin was as effective as AmBisome in empirical therapy of persistent febrile neutropenia (see Table 9).
Table 9: Favorable Response of Patients with Persistent Fever and Neutropenia
|Caspofungin*||AmBisome*||% Difference (Confidence Interval)†|
|Number of Patients ‡||556||539|
|Overall Favorable Response||190 (33.9%)||181 (33.7%)||0.2 (-5.6, 6.0)|
|No documented breakthrough fungal infection||527 (94.8%)||515 (95.5%)||-0.8|
|Survival 7 days after end of treatment||515 (92.6%)||481 (89.2%)||3.4|
|No discontinuation due to toxicity or lack of efficacy||499 (89.7%)||461 (85.5%)||4.2|
|Resolution of fever during neutropenia||229 (41.2%)||223 (41.4%)||-0.2|
|* Caspofungin: 70 mg on Day 1, then 50 mg once daily for the remainder of treatment (daily dose increased to 70 mg for 73 patients); AmBisome: 3 mg/kg/day (daily dose increased to 5 mg/kg for 74 patients).† Overall Response: estimated % difference adjusted for strata and expressed as caspofungin – AmBisome (95.2% CI); Individual criteria presented above are not mutually exclusive. The percent difference calculated as caspofungin – AmBisome.‡ Analysis population excluded subjects who did not have fever or neutropenia at study entry.|
The rate of successful treatment of documented baseline infections, a component of the primary endpoint, was not statistically different between treatment groups.
The response rates did not differ between treatment groups based on either of the stratification variables: risk category or prior antifungal prophylaxis.
14.2 Candidemia and the Following other Candida Infections: Intra-Abdominal Abscesses, Peritonitis and Pleural Space Infections
In a randomized, double-blind study, patients with a proven diagnosis of invasive candidiasis received daily doses of caspofungin (50 mg/day following a 70 mg loading dose on Day 1) or amphotericin B deoxycholate (0.6 to 0.7 mg/kg/day for non-neutropenic patients and 0.7 to 1 mg/kg/day for neutropenic patients). Patients were stratified by both neutropenic status and APACHE II score. Patients with Candida endocarditis, meningitis, or osteomyelitis were excluded from this study.
Patients who met the entry criteria and received one or more doses of IV study therapy were included in the modified intention-to-treat [MITT] analysis of response at the end of IV study therapy. A favorable response at this time point required both symptom/sign resolution/improvement and microbiological clearance of the Candida infection.
Two hundred thirty-nine patients were enrolled. Patient disposition is shown in Table 10.Table 10: Disposition in Candidemia and Other Candida Infections (Intra-abdominal abscesses, peritonitis, and pleural space infections)
|Patients completing study†||63 (55.3%)||69 (55.2%)|
|DISCONTINUATIONS OF STUDY†|
|All Study Discontinuations||51 (44.7%)||56 (44.8%)|
|Study Discontinuations due to clinical adverse events||39 (34.2%)||43 (34.4%)|
|Study Discontinuations due to laboratory adverse events||0 (0%)||1 (0.8%)|
|DISCONTINUATIONS OF STUDY THERAPY|
|All Study Therapy Discontinuations||48 (42.1%)||58 (46.4%)|
|Study Therapy Discontinuations due to clinical adverse events||30 (26.3%)||37 (29.6%)|
|Study Therapy Discontinuations due to laboratory adverse events||1 (0.9%)||7 (5.6%)|
|Study Therapy Discontinuations due to all drug-related‡ adverse events||3 (2.6%)||29 (23.2%)|
|* Patients received caspofungin 70 mg on Day 1, then 50 mg once daily for the remainder of their treatment.† Study defined as study treatment period and 6-8 week follow-up period.‡ Determined by the investigator to be possibly, probably, or definitely drug-related.|
Of the 239 patients enrolled, 224 met the criteria for inclusion in the MITT population (109 treated with caspofungin and 115 treated with amphotericin B). Of these 224 patients, 186 patients had candidemia (92 treated with caspofungin and 94 treated with amphotericin B). The majority of the patients with candidemia were non-neutropenic (87%) and had an APACHE II score less than or equal to 20 (77%) in both arms. Most candidemia infections were caused by C. albicans (39%), followed by C. parapsilosis (20%), C. tropicalis (17%), C. glabrata (8%), and C. krusei (3%).
At the end of IV study therapy, caspofungin was comparable to amphotericin B in the treatment of candidemia in the MITT population. For the other efficacy time points (Day 10 of IV study therapy, end of all antifungal therapy, 2-week post-therapy follow-up, and 6- to 8-week post-therapy follow-up), caspofungin was as effective as amphotericin B.
Outcome, relapse and mortality data are shown in Table 11.
Table 11: Outcomes, Relapse, & Mortality in Candidemia and Other Candida Infections (Intra-abdominal abscesses, peritonitis, and pleural space infections)
|Caspofungin*||Amphotericin B||% Difference† after adjusting for strata (Confidence Interval)‡|
|Number of MITT§ patients||109||115|
|FAVORABLE OUTCOMES (MITT) AT THE END OF IV STUDY THERAPY|
|All MITT patients||81/109 (74.3%)||78/115 (67.8%)||7.5 (-5.4, 20.3)|
|Candidemia||67/92 (72.8%)||63/94 (67.0%)||7.0 (-7.0, 21.1)|
|Neutropenic||6/14 (43%)||5/10 (50%)|
|Non-neutropenic||61/78 (78%)||58/84 (69%)|
|Blood / Pleural||1/1||1/1|
|Blood / Peritoneal||1/1||1/1|
|Blood / Urine||–||1/1|
|Peritoneal / Pleural||1/2||–|
|Abdominal / Peritoneal||–||1/1|
|Subphrenic / Peritoneal||1/1||–|
|DISSEMINATED INFECTIONS, RELAPSES AND MORTALITY|
|Disseminated Infections in neutropenic patients||4/14 (28.6%)||3/10 (30.0%)|
|All relapses¶||7/81 (8.6%)||8/78 (10.3%)|
|Culture-confirmed relapse||5/81 (6%)||2/78 (3%)|
|Overall study# mortality in MITT||36/109 (33.0%)||35/115 (30.4%)|
|Mortality during study therapy||18/109 (17%)||13/115 (11%)|
|Mortality attributed to Candida||4/109 (4%)||7/115 (6%)|
|* Patients received caspofungin 70 mg on Day 1, then 50 mg once daily for the remainder of their treatment.† Calculated as caspofungin – amphotericin B ‡ 95% CI for candidemia, 95.6% for all patients § Modified intention-to-treat ¶ Includes all patients who either developed a culture-confirmed recurrence of Candida infection or required antifungal therapy for the treatment of a proven or suspected Candida infection in the follow-up period.# Study defined as study treatment period and 6-8 week follow-up period.|
In this study, the efficacy of caspofungin in patients with intra-abdominal abscesses, peritonitis and pleural space Candida infections was evaluated in 19 non-neutropenic patients. Two of these patients had concurrent candidemia. Candida was part of a polymicrobial infection that required adjunctive surgical drainage in 11 of these 19 patients. A favorable response was seen in 9 of 9 patients with peritonitis, 3 of 4 with abscesses (liver, parasplenic, and urinary bladder abscesses), 2 of 2 with pleural space infections, 1 of 2 with mixed peritoneal and pleural infection, 1 of 1 with mixed abdominal abscess and peritonitis, and 0 of 1 with Candida pneumonia.
Overall, across all sites of infection included in the study, the efficacy of caspofungin was comparable to that of amphotericin B for the primary endpoint.
In this study, the efficacy data for caspofungin in neutropenic patients with candidemia were limited. In a separate compassionate use study, 4 patients with hepatosplenic candidiasis received prolonged therapy with caspofungin following other long-term antifungal therapy; three of these patients had a favorable response. In a second randomized, double-blind study, 197 patients with proven invasive candidiasis received caspofungin 50 mg/day (following a 70 mg loading dose on Day 1) or caspofungin 150 mg/day. The diagnostic criteria, evaluation time points, and efficacy endpoints were similar to those employed in the prior study. Patients with Candida endocarditis, meningitis, or osteomyelitis were excluded. Although this study was designed to compare the safety of the two doses, it was not large enough to detect differences in rare or unexpected adverse events [see Adverse Reactions (6.1)]. The efficacy of caspofungin at the 150 mg daily dose was not significantly better than the efficacy of the 50 mg daily dose of caspofungin. The efficacy of doses higher than 50 mg daily in the other adult patients for whom caspofungin is indicated has not been evaluated.
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