The Evolution of Antifungal Therapy: Introduction to Rezafungin and Emerging Echinocandin Uses

Introduction to Rezafungin and Emerging Echinocandin Uses

Infectious Disease · Seminar week 21 · released August 6, 2026 · includes a discussion video

Rezafungin has been recently approved as a long-acting echinocandin with significant implications for outpatient parenteral antimicrobial therapy (OPAT) due to its once-weekly…

Learning Objectives

• Describe how echinocandins disrupt fungal cell-wall synthesis and relate this mechanism to spectrum, resistance, and tissue-site limitations.
• Apply rezafungin pharmacokinetics, labeled dosing, safety monitoring, and missed-dose protocols to clinical care.
• Critically interpret the STRIVE and ReSTORE efficacy and safety data without equating noninferiority with superiority.
• Construct a candidemia management plan integrating prompt therapy, susceptibility testing, source control, clearance cultures, and appropriate duration.
• Compare rezafungin with caspofungin, micafungin, and anidulafungin using patient-, pathogen-, and setting-specific variables.
• Evaluate emerging and off-label echinocandin applications according to the maturity of their supporting evidence.
• Respond systematically to suspected multidrug-resistant Candida, including Candida auris and FKS-mediated echinocandin resistance.

Introduction to Rezafungin and Echinocandins

%%FIG0%% The history of systemic antifungal therapy is a progression from broad toxicity toward selective fungal targets. Amphotericin B transformed the treatment of invasive mycoses but brought infusion reactions, nephrotoxicity, electrolyte wasting, and difficult administration. Azoles offered oral therapy and a broader range of formulations, yet introduced variable absorption, CYP-mediated interactions, hepatotoxicity, QT effects, and increasingly important resistance. Echinocandins—caspofungin in 2001, followed by micafungin and anidulafungin—created a third strategy: attack a cell-wall component absent from mammalian cells. Rezafungin retains that target but redesigns exposure, using exceptional chemical stability and a terminal half-life near one week to convert a daily intravenous class into a once-weekly regimen.

Teaching Point: β-1,3-D-glucan synthase contains a catalytic transmembrane Fks protein and regulatory Rho1. It polymerizes UDP-glucose into β-1,3-D-glucan, a structural scaffold that helps fungal cells withstand osmotic stress. Echinocandin-mediated glucan depletion produces wall instability and concentration-dependent fungicidal activity against most Candida. In Aspergillus, injury is concentrated at growing hyphal tips and branch points, producing predominantly fungistatic activity rather than reliable monotherapy. Recent cryo-electron microscopy refines the traditional description of simple “noncompetitive inhibition”: caspofungin can form a complex with Fks1 and nascent glucan that stalls polymer translocation (PMID: 42020744).

The class is active against many azole-susceptible and azole-resistant Candida isolates. However, C. parapsilosis and C. guilliermondii characteristically have higher echinocandin MICs because of native Fks sequence variation; this is not synonymous with universal clinical resistance. Echinocandins lack dependable activity against Cryptococcus, Mucorales, Fusarium, and most endemic dimorphic fungi. Their clinical spectrum is also constrained by pharmacology: active-drug concentrations are poor in urine, cerebrospinal fluid, and the aqueous and vitreous compartments.

Nuance: A positive blood culture for Candida is never a contaminant to dismiss. Yet “candidemia” is not a complete diagnosis. The clinician must determine whether the bloodstream is the entire recognized compartment or a signal from an infected catheter, thrombophlebitis, intra-abdominal collection, endocarditis, hepatosplenic disease, osteomyelitis, or ocular dissemination. Drug selection follows that anatomic assessment. An echinocandin that is excellent in blood may be inadequate in the eye, central nervous system, or urinary collecting system.

Rezafungin was approved in the United States in 2023 and subsequently in Europe. The current U.S. indication is specifically for adults with candidemia or invasive candidiasis who have limited or no alternative options; the label emphasizes limited clinical data and notes that Candida endocarditis, osteomyelitis, and meningitis were not studied (U.S. prescribing information). The European indication is broader—adult invasive candidiasis—but local labeling and formulary criteria remain controlling (EMA product information). These distinctions matter when convenience is the principal reason for considering treatment. The first-approval review is PMID: 37212966, while the subsequent clinical review is PMID: 39913021.

Framework: For suspected invasive candidiasis, move through five questions: Is immediate empiric therapy justified? What species and susceptibility pattern are likely? Where is the infection anatomically? What source or device requires intervention? Can the eventual regimen be safely delivered after discharge?

MUST ACT: In septic shock or high-probability invasive candidiasis, obtain appropriate cultures without delaying antifungal therapy. Repeat blood cultures daily or every other day until clearance, pursue source control, and define duration from the first documented negative culture—not from the first dose.

Audience Poll: Which feature most often changes your initial echinocandin plan: species identification, persistent blood-culture positivity, an infected device, or discovery of a sanctuary-site infection?

Rezafungin Pharmacokinetics and Dosing

%%FIG1%% Rezafungin illustrates why the shape of an exposure curve can matter as much as total dose. Echinocandin efficacy correlates principally with AUC/MIC and peak/MIC relationships. A 400-mg loading dose provides high exposure immediately, when fungal burden and the risk of clinical deterioration are greatest; weekly 200-mg doses then sustain concentrations. In patients with candidemia or invasive candidiasis, mean terminal half-life is 152 ± 29 hours, clearance is approximately 0.35 L/hour, and volume of distribution is about 67 L. The day-1 mean AUC over 168 hours is approximately 827 μg·h/mL, compared with 667 μg·h/mL after the day-15 dose. This “front loading” is biologically attractive, but it should not be translated into an unproven claim of superior clearance, survival, or resistance prevention.

MUST ACT: Administer 400 mg intravenously on day 1, then 200 mg on day 8 and every seven days thereafter. Infuse each dose over approximately one hour. U.S. safety has not been established beyond four weekly doses; European information beyond four weeks is limited. The interval does not alter the conventional requirement to treat uncomplicated candidemia for at least 14 days after documented bloodstream clearance and resolution of attributable symptoms.

A missed dose should be given as soon as possible. If administered within three days of its assigned date, retain the original weekly schedule. If more than three days late, reset the schedule so at least four days separate doses. After an interruption of two weeks or longer, restart with a 400-mg loading dose. This protocol should be written explicitly into OPAT orders; “weekly” without an anchor date invites dosing errors.

Rezafungin is highly protein bound and is eliminated mainly through fecal excretion, with no observed hepatic metabolism and minimal active renal elimination. Clinically meaningful PK changes have not been demonstrated with renal impairment, hemodialysis, Child-Pugh B or C hepatic impairment, age, sex, or body weight. It is not expected to be dialyzable, and no renal or hepatic dosage adjustment is recommended. Formal interaction studies found no clinically important effect on representative CYP or transporter substrates, including tacrolimus, cyclosporine, midazolam, digoxin, statins, metformin, venetoclax, ibrutinib, or mycophenolate (PMID: 37154682). This is particularly valuable in transplantation and hematologic malignancy, where azole–immunosuppressant interactions can dominate prescribing.

Nuance: “No dose adjustment” is not the same as “no monitoring.” Baseline and follow-up liver tests and electrolytes are appropriate, especially in critically ill patients receiving multiple hepatotoxic or electrolyte-altering drugs. Common trial adverse reactions included hypokalemia, fever, diarrhea, anemia, nausea, vomiting, hypomagnesemia, and hypophosphatemia. Hypersensitivity and anaphylaxis have been reported. Flushing, warmth, urticaria, nausea, or chest tightness during infusion should prompt slowing or pausing the infusion and reassessment. Patients should also receive photosensitivity counseling and ultraviolet-protection advice.

Poor urinary, ocular, and CNS exposure remains a class limitation despite the long plasma half-life. Rezafungin should not be chosen for Candida cystitis, ascending pyelonephritis, endophthalmitis, chorioretinitis, or meningitis merely because serum concentrations remain measurable. A long half-life can also be a liability: once administered, exposure cannot be rapidly withdrawn if serious toxicity occurs or the organism proves resistant.

Decision Point: Weekly administration adds the most value when a patient is stable, has cleared blood cultures and adequate source control, lacks a reliable oral azole option, requires continued echinocandin therapy, and would otherwise need a central line or daily infusion encounter. It adds much less when the patient can take susceptible oral fluconazole, still requires another daily IV drug, or has an unresolved focus requiring hospitalization.

Teaching Point: Rezafungin may permit intermittent peripheral access rather than a PICC placed solely for daily antifungal therapy, but that is a program-level decision. Reliable transportation, infusion capacity, laboratory surveillance, rapid access to clinical reassessment, and a clearly documented treatment endpoint remain mandatory.

Audience Poll: Does once-weekly dosing make you more comfortable discharging a patient, or does the long, non-reversible exposure make you more selective?

Clinical Trial Data: STRIVE and RESTORE Studies

%%FIG2%% STRIVE was a phase 2, randomized, double-blind, double-dummy, dose-ranging trial conducted at 44 centers in ten countries. It randomized 207 adults to rezafungin 400 mg weekly, rezafungin 400 mg followed by 200 mg weekly, or caspofungin 70 mg once followed by 50 mg daily, with optional fluconazole step-down in the caspofungin arm. Among 183 microbiological intention-to-treat participants, day-14 overall cure—clinical resolution plus mycological eradication—was 60.5%, 76.1%, and 67.2%, respectively. Day-30 all-cause mortality was 15.8%, 4.4%, and 13.1%. Median blood-culture clearance was 19.5 hours for pooled rezafungin versus 22.8 hours for caspofungin, an exploratory comparison. STRIVE supported selection of the 400/200-mg regimen but was not powered for formal inferential noninferiority (PMID: 32955088).

Teaching Point: STRIVE did not “prove noninferiority.” Its favorable 400/200-mg result was generated in a small dose-finding cohort and should not be interpreted as evidence that this regimen reduces mortality compared with either 400 mg weekly or caspofungin.

ReSTORE was the pivotal phase 3 study: 199 adults were randomized at 66 centers in 15 countries, and 187 culture-confirmed participants comprised the modified intention-to-treat population. Rezafungin 400/200 mg weekly was compared with daily caspofungin, again allowing oral fluconazole step-down only in the caspofungin group. For the EMA primary endpoint, day-14 global cure was 59.1% with rezafungin and 60.6% with caspofungin; the weighted difference was −1.1 percentage points (95% CI, −14.9 to 12.7). For the FDA primary endpoint, day-30 all-cause mortality was 23.7% versus 21.3%; the difference was 2.4 points (95% CI, −9.7 to 14.4). Both met the prespecified 20-percentage-point noninferiority margins (PMID: 36442484).

Day-14 clinical cure was 66.7% versus 67.0%, and mycological eradication or presumed eradication was 67.7% versus 66.0%. Median time to negative blood culture—23.9 versus 27.0 hours—was not significantly different. At least one treatment-emergent adverse event occurred in 91% versus 85%, and serious adverse events in 56% versus 53%; no new concerning safety pattern emerged.

Nuance: Noninferiority is not equivalence, and a 20-point margin is clinically generous. ReSTORE was relatively small, sponsor-funded, and composed predominantly of nonneutropenic patients with APACHE II scores below 20 and candidemia without a deep focus. It excluded endocarditis, osteomyelitis, CNS and ocular candidiasis, chronic disseminated candidiasis, and selected urinary infections. A later China-extension analysis supported similar results but was an extension of the same development program, not a wholly independent confirmatory trial (PMID: 41018703).

Clinical Case: Converting Trial Evidence Into a Discharge Plan

A 68-year-old woman with diabetes and stage 3 chronic kidney disease develops septic shock eight days after colectomy for perforated diverticulitis. She has received broad-spectrum antibiotics and parenteral nutrition through a central line. Two blood-culture sets grow yeast. Micafungin 100 mg IV daily is started immediately; the central line is removed when alternative access is obtained, repeat cultures are drawn daily, and CT shows a postoperative collection that is drained.

The isolate is Candida glabrata, resistant to fluconazole and voriconazole but susceptible to anidulafungin and micafungin. Blood cultures clear after 48 hours. She improves, stops IV antibacterial therapy, tolerates oral nutrition, and has no murmur, embolic signs, focal bone pain, neurologic findings, visual symptoms, prosthetic valve, or persistent candidemia.

Decision Point: Oral step-down is unreliable, but hospitalization is no longer needed. Daily micafungin OPAT is valid. In the United States, rezafungin is also considered because she has no dependable oral alternative and ongoing daily IV therapy is the remaining discharge barrier. After infectious-diseases and pharmacy review, she receives a 400-mg rezafungin loading dose, with 200 mg planned seven days later.

MUST ACT: The weekly regimen does not excuse incomplete staging or shorten therapy. The first negative culture date is recorded, treatment continues for at least 14 days beyond that date with clinical resolution, and recurrence triggers renewed cultures and evaluation for the abdominal source, thrombophlebitis, endocarditis, or resistance. Rezafungin created logistical value only after clearance and source control were demonstrated.

Audience Poll: Would you choose weekly rezafungin, daily micafungin OPAT, or continued hospitalization—and which assumption determines your answer?

Economic Models for Antifungal Therapy

%%FIG3%% The relevant economic comparison is not price per vial but cost per successfully treated episode. Drug acquisition is only one component. A credible analysis includes compounding, infusion time, vascular access, nursing, laboratory monitoring, adverse-event management, transportation, OPAT coordination, readmissions, inpatient and ICU days, and the opportunity cost of an occupied bed. These costs fall on different stakeholders; a regimen can create hospital capacity without producing cash-releasing savings for the pharmacy or payer.

Framework: Cost-minimization asks which treatment costs less when clinical outcomes are assumed equivalent. Cost-effectiveness measures cost per clinical success or life-year. Cost-utility introduces quality-adjusted life-years, and budget-impact analysis asks whether an institution can afford adoption over a defined period. ReSTORE makes cost-minimization a reasonable scenario analysis, but noninferiority does not prove that every downstream resource outcome is identical.

Rezafungin’s economic proposition is principally operational. For patients who truly require an IV echinocandin, one infusion may replace seven daily administrations. That can reduce pharmacy preparation, nursing encounters, infusion-center visits, transportation, and line manipulation. A peripheral IV may sometimes replace a PICC maintained solely for daily antifungal dosing. These benefits diminish when a patient requires concurrent daily antibacterials, wound care, dialysis, rehabilitation, or another reason for inpatient treatment.

Decision Point: Test oral step-down before comparing IV regimens. A clinically stable patient with negative follow-up cultures and a fluconazole-susceptible isolate usually has a less expensive and less invasive option than any echinocandin. Rezafungin’s strongest economic niche is the patient with azole resistance, intolerance, important interactions, unreliable absorption, or another reason oral therapy cannot be trusted.

A U.S. hospital analysis identified mean post-culture costs of approximately $50,000 for candidemia and $62,000 for invasive candidiasis without candidemia. Among survivors still receiving an echinocandin near discharge, 42.9% met database-derived criteria for possible earlier discharge, identifying a theoretical target rather than proving discharge safety (PMID: 38213636). In a separate OPAT cohort, substituting weekly for daily echinocandin therapy reduced modeled administration encounters by 52%, but nearly one-third of patients also required parenteral antibacterials, substantially eroding the advantage (PMID: 39259571).

A post hoc pooled STRIVE/ReSTORE analysis reported mean hospital stays of 25.2 versus 28.3 days and ICU stays of 16.1 versus 21.6 days with rezafungin and caspofungin. After adjustment for an imbalance in baseline mechanical ventilation, the estimated ICU difference was 4.1 days, with a confidence interval compatible with no difference. The trials were double-dummy studies, so rezafungin recipients still received daily placebo infusions; early discharge was not prospectively tested (PMID: 39529079).

A German model applied an assumed five-day ICU reduction to selected cases and estimated a median saving of €7,175, but omitted rezafungin acquisition cost and treated resource consumption simplistically (PMID: 37342199). A 2026 manufacturer-funded UK model estimated savings of £6,028–£6,727 versus daily echinocandins and a small modeled QALY gain. Results were driven mainly by ICU stay and mortality assumptions; drug costs represented only 1%–13% of total modeled costs (PMID: 41674218).

Nuance: A freed bed is often a capacity gain, not money returned to the budget. Local conclusions may reverse with acquisition price, outpatient reimbursement, generic comparator cost, oral-step-down frequency, or the need for other IV therapy.

MUST ACT: Before labeling rezafungin cost-saving, model your actual eligible population, formulary restrictions, discharge pathway, infusion capacity, concomitant therapy, and payer mix. Subscription-style antimicrobial payment models address development and procurement incentives; they are not evidence that rezafungin lowers episode-level costs.

Audience Poll: Which variable is most likely to overturn your institution’s result: acquisition price, ICU length of stay, oral-step-down eligibility, or concurrent daily IV therapy?

Emerging Uses and Off-label Applications

%%FIG4%% Emerging use should be divided into three evidentiary tiers: established class use, plausible rezafungin extension, and experimental application. Blurring these categories can turn pharmacologic enthusiasm into unsafe prescribing.

The most advanced expansion is prophylaxis after allogeneic hematopoietic stem-cell transplantation. Conventional prophylaxis often requires an azole for Candida and moulds plus trimethoprim–sulfamethoxazole for Pneumocystis, creating interactions and overlapping hepatic, renal, marrow, and electrolyte toxicities. ReSPECT compared once-weekly rezafungin with a standard antimicrobial regimen for preventing Candida, Aspergillus, and Pneumocystis disease. In April 2026, the sponsor reported day-90 fungal-free survival of 60.7% with rezafungin versus 59.0% with standard prophylaxis, meeting the stated noninferiority endpoint (company-reported topline results). As of July 2026, these were not yet peer-reviewed results and prophylaxis was not a U.S.-labeled indication.

Nuance: A positive press release is a signal, not a practice guideline. Full denominators, event adjudication, organism-specific outcomes, mortality, adverse events, missing-data handling, and subgroup performance must be reviewed before replacing established prophylaxis.

Pneumocystis jirovecii is particularly interesting because its ascus or cyst form contains β-glucan. Rezafungin reduced pulmonary burden and prevented disease in animal models (PMID: 34575785). However, echinocandins preferentially affect the cystic stage and may leave trophic forms inadequately treated. A registered phase 2 study has therefore evaluated rezafungin combined with a shortened course of trimethoprim–sulfamethoxazole rather than assuming safe monotherapy. Human evidence otherwise consists mainly of isolated reports. Rezafungin should not replace TMP–SMX or validated alternatives for treatment or prophylaxis outside a protocol or expert-directed rescue situation.

For invasive aspergillosis, caspofungin is approved as salvage therapy when standard treatment is refractory or intolerable, and micafungin is sometimes used in salvage regimens. Echinocandin monotherapy is not preferred primary treatment for invasive pulmonary aspergillosis; selected patients with documented severe disease may receive an azole plus an echinocandin, although the benefit remains uncertain (IDSA aspergillosis guideline, PMID: 27365388). Rezafungin has in-vitro and animal activity against Aspergillus, including some azole-resistant isolates, but treatment of invasive aspergillosis is not established.

Framework: For a proposed off-label use, ask: Does the organism express the target? Does active drug reach the infected compartment? Is the evidence in vitro, animal, observational, or randomized? Is there an established alternative? What source-control intervention matters more than extending the dosing interval?

Echinocandins have useful activity against Candida biofilms, supporting their role in catheter- and device-associated infection. Yet antifungal therapy does not sterilize retained hardware reliably. Catheter removal, valve surgery when feasible, drainage, or device extraction remains central. For Candida endocarditis, guidelines permit high-dose caspofungin 150 mg/day, micafungin 150 mg/day, or anidulafungin 200 mg/day as alternatives to lipid amphotericin B with or without flucytosine. Rezafungin was excluded from registration studies of endocarditis and should not be substituted solely for convenience.

Traditional echinocandins can also provide initial therapy for osteoarticular candidiasis before prolonged susceptible oral azole treatment, and can treat azole-refractory esophageal or mucosal candidiasis. Chronic mucocutaneous candidiasis, however, requires evaluation for immune defects such as STAT1 gain-of-function or impaired IL-17 signaling, culture and susceptibility testing, and a sustainable suppression strategy. Chronic weekly rezafungin lacks adequate supporting evidence.

Decision Point: OPAT consolidation is currently the most defensible “emerging” rezafungin use because it extends a proven invasive-candidiasis indication into a different delivery pathway. Experimental organism or anatomic indications demand a much higher evidentiary threshold.

MUST ACT: Do not use rezafungin as convenient monotherapy for Candida endophthalmitis, meningitis, urinary-tract disease, endocarditis, osteomyelitis, primary invasive aspergillosis, or PJP without expert review and an evidence-based companion or alternative regimen.

Audience Poll: Which future application is most compelling: transplant prophylaxis, abbreviated combination treatment for PJP, mould-active combination therapy, or long-course outpatient consolidation?

Comparative Analysis with Traditional Echinocandins

%%FIG5%% All four echinocandins share a target and many spectrum limitations, but they are not operationally interchangeable.

Teaching Point: Severe hepatic disease does not automatically mandate anidulafungin. Its nonenzymatic degradation makes it pharmacologically attractive, but micafungin and rezafungin also require no labeled hepatic dose adjustment. Caspofungin is the principal agent requiring reduction in moderate hepatic impairment, and experience in severe hepatic impairment is limited.

Renal failure rarely differentiates these drugs: none requires routine renal adjustment, and dialysis does not meaningfully remove them. Instead, selection turns on treatment setting, anticipated duration, interactions, hepatic considerations, approved indication, and the likelihood of oral step-down. Anidulafungin is useful when avoiding metabolic interactions is paramount. Micafungin has extensive clinical experience and a prophylaxis indication. Caspofungin offers the broadest set of established indications, including empiric treatment of suspected fungal infection in febrile neutropenia and salvage aspergillosis. Rezafungin provides uniquely sustained exposure.

Decision Point: If susceptibility is expected and oral fluconazole step-down is likely within five to seven days, an inexpensive daily echinocandin followed by oral therapy may be more flexible. If no oral option exists and daily administration is the principal barrier to discharge, rezafungin becomes more attractive.

The daily agents can be stopped quickly when toxicity, resistance, or a new diagnosis emerges. Rezafungin cannot be “turned off”; measurable exposure persists for weeks. Conversely, missed daily doses or inconsistent OPAT delivery are less likely with weekly therapy. This tradeoff is especially important when preliminary yeast identification is uncertain or a deep focus has not been excluded.

Nuance: Class membership does not guarantee identical MICs, and an MIC should not be compared across drugs without the correct CLSI or EUCAST species-specific breakpoint. C. parapsilosis commonly has higher echinocandin MICs yet may still respond clinically. Caspofungin MIC testing is comparatively variable between laboratories; micafungin or anidulafungin testing and reference-laboratory confirmation can better characterize suspected class resistance.

All echinocandins penetrate urine, CSF, and the eye poorly. Higher serum exposure does not erase that limitation. Likewise, obesity and critical illness can alter daily echinocandin exposure, but evidence does not support improvising rezafungin doses beyond the approved regimen. Routine therapeutic drug monitoring is not established for the class.

Safety is generally favorable relative to amphotericin B and many azoles. Infusion-related histamine phenomena and hepatic-test abnormalities can occur with every agent. Rezafungin additionally carries explicit photosensitivity counseling and a prolonged exposure tail. Micafungin has several modest interaction considerations, while caspofungin exposure can change with enzyme-inducing drugs. Anidulafungin has the cleanest conventional interaction profile.

Framework: Choose an echinocandin by matching five domains: organism and MIC, anatomic site, organ function and interactions, need for rapid reversibility, and delivery pathway.

MUST ACT: Never let the dosing schedule overrule site biology. Suspected ocular, CNS, urinary, valvular, or bone infection requires a site-specific regimen and duration, not simply the longest-acting echinocandin.

Audience Poll: Which attribute matters most in your practice: once-weekly delivery, reversibility, hepatic simplicity, prophylaxis experience, or formulary cost?

Discussion on Multi-drug Resistant Challenges in Treatment

%%FIG6%% Echinocandin resistance is primarily target modification, not inadequate drug entry. Hotspot substitutions in FKS1 or FKS2 reduce glucan-synthase sensitivity and usually confer cross-resistance across the class. C. glabrata—now also termed Nakaseomyces glabratus—is especially capable of acquiring these mutations during prolonged or repeated exposure. In one clinical cohort, echinocandin treatment failure occurred in 60% of infections involving FKS mutants versus 23% without such mutations (PMID: 24879785). Stress-response pathways and increased chitin production can produce tolerance or paradoxical growth in vitro, but neither finding justifies unvalidated bedside dose escalation.

MUST ACT: Rezafungin is not a class-resistance workaround. Its label explicitly recognizes some cross-resistance with FKS mutations that reduce susceptibility to other echinocandins. Switching from micafungin or caspofungin to rezafungin without susceptibility evidence is not an adequate response to suspected FKS-mediated failure.

Persistent candidemia has a broader differential than resistance. A retained catheter, undrained abdominal source, infected thrombus, prosthetic material, endocarditis, sanctuary-site disease, delayed therapy, or an incorrect diagnosis is often more likely. Repeat cultures, species identification, source control, imaging directed by symptoms, and susceptibility testing should occur in parallel rather than sequentially.

Framework: When blood cultures remain positive, audit six domains: drug, dose, delivery, organism, compartment, and source. Confirm that the dose reached the patient; verify species and MICs; look for FKS-mediated resistance; identify poorly penetrated compartments; remove infected hardware where feasible; and drain or debride the source.

The 2025 ECMM/ISHAM/ASM global guideline strongly recommends standardized CLSI or EUCAST susceptibility testing for invasive isolates and identifies echinocandins, including rezafungin where appropriate, as first-line treatment for most invasive candidiasis outside ocular and CNS disease (PMID: 39956121). Testing is particularly important after prior echinocandin exposure and for C. glabrata, C. parapsilosis, or C. auris. If caspofungin MIC results conflict with clinical behavior, request anidulafungin or micafungin testing and reference-laboratory confirmation; FKS sequencing can clarify discordant phenotypic results.

C. auris, recently reclassified as Candidozyma auris, combines antifungal resistance with prolonged skin colonization, environmental persistence, outbreak potential, and frequent laboratory misidentification. Echinocandins remain preferred initial therapy for invasive infection in adults, but susceptibility testing, infection-prevention notification, contact precautions, appropriate environmental disinfection, and public-health coordination are essential. Colonization without clinical infection should not be treated. Contemporary U.S. genomic surveillance found FKS1 hotspot mutations in 92% of tested echinocandin-resistant isolates, illustrating the tight relationship between target mutation and class failure (CDC Emerging Infectious Diseases, 2026).

Decision Point: If invasive C. auris is echinocandin resistant or the patient fails to improve after approximately five days despite adequate source control, CDC guidance supports considering liposomal amphotericin B 5 mg/kg/day with expert consultation (CDC clinical guidance). For other proven azole- and echinocandin-resistant invasive Candida, lipid amphotericin B 3–5 mg/kg/day is generally the immediate alternative. Combination therapy, flucytosine, or a site-specific regimen may be appropriate for endocarditis, CNS disease, or other complex foci, but should be individualized with infectious-diseases and mycology expertise.

C. parapsilosis presents a different challenge: naturally higher echinocandin MICs coexist with increasingly reported fluconazole-resistant outbreaks. The correct response is not an automatic class switch but species-level susceptibility interpretation, source control—particularly catheter management—and close microbiological follow-up. The changing epidemiology of non-albicans Candida and resistance is reviewed in PMID: 40872317.

Nuance: High front-loaded rezafungin exposure might theoretically suppress less-susceptible subpopulations, but clinical prevention of resistance has not been demonstrated. Pooled trial subgroup analyses were too small to establish efficacy against FKS-mutant or pan-resistant infections.

New glucan-synthase inhibitors and agents targeting other fungal pathways may eventually expand salvage options, but access, regulatory status, susceptibility methods, and clinical evidence remain uneven. Until then, the most powerful resistance strategy is stewardship: treat invasive disease promptly, avoid treating colonization, obtain species-level identification, use validated doses, de-escalate when safe, limit unnecessary prophylaxis, and control the source.

Teaching Point: Multidrug resistance is a systems problem as well as a drug problem. The bedside response combines pharmacology, microbiology, surgery or interventional source control, infection prevention, surveillance, and public-health communication.

Audience Poll: In persistent candidemia, which error is most dangerous: assuming resistance without source control, assuming susceptibility from the drug’s novelty, or treating colonization as invasive disease?

Conclusion

Rezafungin is an advance in exposure engineering rather than a new antifungal target. Its 400-mg loading dose, approximately 152-hour half-life, minimal interaction burden, and weekly maintenance create a meaningful option for selected adults who require continued echinocandin therapy—particularly when no reliable oral step-down exists and daily infusion is the remaining barrier to discharge.

STRIVE established dose-selection and supportive efficacy data; ReSTORE formally demonstrated noninferiority to caspofungin for day-14 global cure and day-30 all-cause mortality. Neither trial demonstrated superiority, universal cost savings, effectiveness at sanctuary sites, or reliable activity against FKS-mediated resistance. The clinical value of rezafungin therefore depends on disciplined patient selection, accurate anatomic staging, susceptibility testing, documented clearance, source control, and a reliable follow-up pathway.

The emerging prophylaxis, Pneumocystis, Aspergillus, biofilm, and long-course consolidation programs are scientifically important, but they occupy different levels of evidence. The mature clinician distinguishes promising pharmacology from a validated indication—and never allows dosing convenience to replace the fundamentals of invasive-candidiasis care.

Tonight on Shift

• Treat candidemia immediately: obtain cultures and start an appropriate echinocandin promptly in an unstable or high-risk patient; never dismiss Candida in blood as contamination.

• Prove clearance and start the duration clock correctly: repeat cultures daily or every other day, then treat uncomplicated candidemia for at least 14 days after the first negative culture and clinical resolution.

• Control the source: remove a plausibly infected catheter when safely feasible, drain collections, and investigate persistent positivity for thrombophlebitis, endocarditis, retained hardware, or metastatic disease.

• Interrogate the isolate: obtain species identification and appropriate azole and echinocandin susceptibility testing; never assume rezafungin overcomes FKS-mediated class resistance.

• Use rezafungin precisely: confirm indication and site suitability, give 400 mg IV once followed by 200 mg weekly, monitor liver tests and electrolytes, counsel about infusion reactions and photosensitivity, and remember the limited safety experience beyond four doses.

• Discharge the patient—not merely the dosing interval: require hemodynamic stability, source control, documented clearance, exclusion of a deep focus, a defined endpoint, reliable infusion access, laboratory monitoring, and rapid clinical follow-up.

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