Effects of inoculum, pH, and cations on the in vitro activity of fidaxomicin (OPT-80, PAR-101) against Clostridium difficile

Fidaxomicin's Role in Overcoming Vancomycin Failure in Clostridium difficile Infections: A Case Series and Literature Review

Clostridium difficile infection (CDI), characterized by diarrheal illness with serious complications, is a common pathology in clinical practice. We present a series of five patients with CDI who underwent treatment with fidaxomicin following the failure of oral vancomycin. To our knowledge, no evidence in the literature suggests that fidaxomicin is more effective than vancomycin in treating acute infection. This paper emphasizes the importance of utilizing a large study to determine the relative effectiveness of vancomycin versus fidaxomicin in treating CDI. We also provide a literature review on CDI and management evolution.

Formal Single Atom Editing of the Glycosylated Natural Product Fidaxomicin Improves Acid Stability and Retains Antibiotic Activity

Fidaxomicin (Fdx) constitutes a glycosylated natural product with excellent antibacterial activity against various Gram-positive bacteria but is approved only for Clostridioides difficile infections. Poor water solubility and acid lability preclude its use for other infections. Herein, we describe our strategy to overcome the acid lability by introducing acid-stable S-linked glycosides. We describe the direct, diastereoselective modification of unprotected Fdx without the need to avoid air or moisture. Using our newly established approach, Fdx was converted to the single atom exchanged analogue S-Fdx, in which the acid labile O-glycosidic bond to the noviose sugar was replaced by the acid stable S-glycosidic bond. Studies of the antibacterial activity of a structurally diverse set of thioglycoside derivatives revealed high potency of acyl derivatives of S-Fdx against Clostridioides difficile (MIC range: 0.12-4 μg/mL) and excellent potency against Clostridium perfringens (MIC range: 0.06-0.5 μg/mL).

Auranofin, at clinically achievable dose, protects mice and prevents recurrence from Clostridioides difficile infection

Clostridioides difficile is the leading cause of nosocomial infections and a worldwide urgent public health threat. Without doubt, there is an urgent need for new effective anticlostridial agents due to the increasing incidence and severity of C. difficile infection (CDI). The aim of the present study is to investigate the in vivo efficacy of auranofin (rheumatoid arthritis FDA-approved drug) in a CDI mouse model and establish an adequate dosage for treatment. The effects of increased C. difficile inoculum, and pre-exposure to simulated gastric intestinal fluid (SGF) and simulated intestinal fluid (SIF), on the antibacterial activity of auranofin were investigated. Auranofin's in vitro antibacterial activity was stable in the presence of high bacterial inoculum size compared to vancomycin and fidaxomicin. Moreover, it maintained its anti-C. difficile activity after being exposed to SGF and SIF. Upon testing in a CDI mouse model, auranofin at low clinically achievable doses (0.125 mg/kg and 0.25 mg/kg) significantly protected mice against CDI with 100% and 80% survival, respectively. Most importantly, auranofin (0.125 mg/kg and 0.25 mg/kg) significantly prevented CDI recurrence when compared with vancomycin. Collectively, these results indicate that auranofin could potentially provide an effective, safe and quick supplement to the current approaches for treating CDI.

Fidaxomicin vs Vancomycin for the Treatment of a First Episode of Clostridium Difficile Infection: A Meta-analysis and Systematic Review

Clostridium difficile infection (CDI) continues to possess a significant disease burden in the United States (US) as well as all over the world. Given the increase in severity and recurrence rate, the decrease in cure rate, and the fact that the virulent ribotype 027 strain remains one of the most commonly identified strains in the US, the Infectious Diseases Society of America (IDSA) published a clinical practice guideline in February 2018 moving away from metronidazole as the first-line treatment for initial CDI and recommending either oral vancomycin or fidaxomicin. The aim of this study is to evaluate the clinical data available comparing the efficacy of primary treatment of CDI between those two antibiotics. We performed a PubMed, PubMed Central, and ScienceDirect database search without restriction to regions, publication types, or languages. A comprehensive literature search was performed from January 1, 1980 up to March 20, 2018. We used the following keywords in different combinations: Clostridium difficile, Clostridium difficile infection, CDI, C. diff, C. difficile, fidaxomicin, vancomycin, pseudomembranous colitis, and antibiotic-associated colitis. The search was limited to human studies. Data were independently extracted by two reviewers with disagreements resolved by a third author. We pooled an odds ratio (OR) on two primary outcomes: Clinical cure rate and rate of recurrence during the follow-up period. The computer search was also supplemented with manual searches by the authors of the retrieved review articles and primary studies. The search phrase “((Clostridium difficile) AND vancomycin) AND fidaxomicin” had the highest yield results. We identified four observational studies with a total of 2,303 patients with CDI that met our inclusion criteria. Compared with vancomycin, fidaxomicin use was associated with a significantly lower recurrence of CDI with a pooled OR of 0.47 (95% confidence interval (CI), 0.37 - 0.60, I2 = 0). On the other hand, there was no significant association of fidaxomicin use with CDI cure rate compared to vancomycin with a pooled OR of 1.22 (95% CI, 0.93 - 1.60, I2 = 0). In light of the recently updated clinical practice guidelines by the IDSA, our review suggests that fidaxomicin has a more sustained clinical response with a statistically significant lower recurrence rate. Although fidaxomicin appears to be the better drug with statistical significance, its cost-effectiveness continues to be an ongoing controversy. More randomized clinical trials are needed to shed light on this matter to assess if there is any clinical significance in fidaxomicin superiority.

Nitroimidazole carboxamides as antiparasitic agents targeting Giardia lamblia, Entamoeba histolytica and Trichomonas vaginalis

Diarrhoeal diseases caused by the intestinal parasites Giardia lamblia and Entamoeba histolytica constitute a major global health burden. Nitroimidazoles are first-line drugs for the treatment of giardiasis and amebiasis, with metronidazole 1 being the most commonly used drug worldwide. However, treatment failures in giardiasis occur in up to 20% of cases and development of resistance to metronidazole is of concern. We have re-examined 'old' nitroimidazoles as a foundation for the systematic development of next-generation derivatives. Using this approach, derivatisation of the nitroimidazole carboxamide scaffold provided improved antiparasitic agents. Thirty-three novel nitroimidazole carboxamides were synthesised and evaluated for activity against G. lamblia and E. histolytica. Several of the new compounds exhibited potent activity against G. lamblia strains, including metronidazole-resistant strains of G. lamblia (EC50 = 0.1-2.5 μM cf. metronidazole EC50 = 6.1-18 μM). Other compounds showed improved activity against E. histolytica (EC50 = 1.7-5.1 μM cf. metronidazole EC50 = 5.0 μM), potent activity against Trichomonas vaginalis (EC50 = 0.6-1.4 μM cf. metronidazole EC50 = 0.8 μM) and moderate activity against the intestinal bacterial pathogen Clostridium difficile (0.5-2 μg/mL, cf. metronidazole = 0.5 μg/mL). The new compounds had low toxicity against mammalian kidney and liver cells (CC50 > 100 μM), and selected antiparasitic hits were assessed for human plasma protein binding and metabolic stability in liver microsomes to demonstrate their therapeutic potential.

Fidaxomicin: A novel agent for the treatment of Clostridium difficile infection

Oral vancomycin and oral metronidazole have several limitations with regard to their use in the treatment of Clostridium difficile infections (CDIs); however, oral vancomycin has been considered the gold standard in clinical trials. In June 2012, fidaxomicin received Health Canada approval for the treatment of CDIs. Its chemistry, mechanisms of action and pharmacological properties are discussed, along with its potential role in CDI therapy.

BACKGROUND:

Due to the limitations of existing treatment options for Clostridium difficile infection (CDI), new therapies are needed.

OBJECTIVE:

To review the available data on fidaxomicin regarding chemistry, mechanisms of action and resistance, in vitro activity, pharmacokinetic and pharmacodynamic properties, efficacy and safety in clinical trials, and place in therapy.

METHODS:

A search of PubMed using the terms “fidaxomicin”, “OPT-80”, “PAR-101”, “OP-1118”, “difimicin”, “tiacumicin” and “lipiarmycin” was performed. All English-language articles from January 1983 to November 2014 were reviewed, as well as bibliographies of all articles.

RESULTS:

Fidaxomicin is the first macrocyclic lactone antibiotic with activity versus C difficile. It inhibits RNA polymerase, therefore, preventing transcription. Fidaxomicin (and its active metabolite OP-1118) is bactericidal against C difficile and exhibits a prolonged postantibiotic effect (approximately 10 h). Other than for C difficile, fidaxomicin demonstrated only moderate inhibitory activity against Gram-positive bacteria and was a poor inhibitor of normal colonic flora, including anaerobes and enteric Gram-negative bacilli. After oral administration (200 mg two times per day for 10 days), fidaxomicin achieved low serum concentration levels but high fecal concentration levels (mean approximately 1400 μg/g stool). Phase 3 clinical trials involving adults with CDI demonstrated that 200 mg fidaxomicin twice daily for 10 days was noninferior to 125 mg oral vancomycin four times daily for 10 days in regard to clinical response at the end of therapy. Fidaxomicin was, however, reported to be superior to oral vancomycin in reducing recurrent CDI and achieving a sustained clinical response (assessed at day 28) for patients infected with non-BI/NAP1/027 strains.

CONCLUSION:

Fidaxomicin was noninferior to oral vancomycin with regard to clinical response at the end of CDI therapy. Fidaxomicin has been demonstated to be as safe as oral vancomycin, but superior to vancomycin in achieving a sustained clinical response for CDI in patients infected with non-BI/NAP1/027 strains. Caution should be exercised in using fidaxomicin monotherapy for treatment of severe complicated CDI because limited data are available. Whether fidaxomicin is cost effective (due to its significantly higher acquisition cost versus oral vancomycin) depends on the acceptable willingness to pay threshold per quality-adjusted life year as a measure of assessing cost effectiveness.

Role of fidaxomicin for the treatment of Clostridium difficile infection

Clostridium difficile is a gram-negative, anaerobic, spore-forming emerging pathogen within health care systems and community-based populations that has a high associated morbidity and mortality as well as cost for the health care system. Recent studies reported high rates of recurrence thus a need for new pharmacological agents to treat C difficile infections (CDIs). Fidaxomicin is a novel macrocyclic antibiotic, originally isolated from fermentation broth of Dactylosporangium aurantiacum spp Hamdenensis, with selective spectrum, unique pharmacokinetic and pharmacodynamics profile, adverse effect profile, efficacy, and role in the treatment of and time to recurrent CDI. Fidaxomicin data have similar clinical cure, when compared to vancomycin, with lower recurrence rates and higher global cure rates in non-BI/NAP1/027 strains. Fidaxomicin also lacks activity against gram-negative bacteria; hence, its potential effect on resistance development among enteric bacteria appears to be low. It appears to have minimal need for renal or hepatic adjustments and minimal concerns for drug-drug interactions. Overall, fidaxomicin has been generally well tolerated with the most common adverse effects reported as mild gastrointestinal complaints. Fidaxomicin appears to have a role in the treatment of CDI with potential lower rates of recurrence, especially in patients with severe disease or risk factors for recurrent CDI.

Antimicrobial activities of fidaxomicin

Fidaxomicin is bactericidal against Clostridium difficile. The combined results of 8 in vitro studies of 1323 C. difficile isolates showed the minimum inhibitory concentration (MIC) range of fidaxomicin to be ≤0.001–1 μg/mL, with a maximum MIC for inhibition of 90% of organisms (MIC₉₀) of 0.5 μg/mL. Isolates from 2 phase III clinical trials demonstrated that fidaxomicin MICs of baseline isolates did not predict clinical cure, failure, or recurrence of C. difficile infections. No resistance to fidaxomicin developed during treatment in either study, although a single strain recovered from a cured patient had an elevated MIC of 16 µg/mL at the time of recurrence. For 135 strains, OP-1118, a major metabolite, had an MIC for inhibition of 50% of organisms of 4 μg/mL and an MIC₉₀ of 8 μg/mL. Changes in inoculum size (10²–10⁵ colony-forming units/spot) or cation concentrations of calcium or magnesium appeared to have no effect on fidaxomicin MICs. Fidaxomicin has little or no activity against gram-negative aerobes and anaerobes or yeast.

Fidaxomicin: a novel macrocyclic antibiotic for the treatment of Clostridium difficile infection

PURPOSE

The pharmacology, clinical efficacy, safety, dosage and administration, and place in therapy of fidaxomicin for the treatment of Clostridium difficile infection (CDI) are reviewed.

SUMMARY

Fidaxomicin, a macrocyclic antibiotic, has a narrow spectrum of activity against gram-positive anaerobes and is bactericidal against C. difficile. It has no activity against gram-negative bacteria. Fidaxomicin has minimal activity against Bacteroides species, which may be advantageous in maintaining colonization resistance and protecting the gastrointestinal tract from colonization by C. difficile. The minimum inhibitory concentration for 90% of organisms for fidaxomicin against C. difficile ranged from 0.0078 to 2 μg/mL in in vitro studies. After oral administration, fecal concentrations are detected and are directly proportional to the dose administered. Fidaxomicin resistance in vivo has not been reported. In clinical trials, fidaxomicin has been shown to be noninferior to vancomycin in the management of mild-to-moderately severe CDI. The adverse-effect profile of fidaxomicin is comparable to that of vancomycin. The recommended dosage for treatment of CDI is fidaxomicin 200 mg orally twice daily for 10 days. Fidaxomicin should be considered for patients who previously received treatment with metronidazole or vancomycin for CDI and who are diagnosed with recurrent CDI in which a non-NAP1/BI/027 strain is isolated. At institutions where strain typing is not available, fidaxomicin may be considered in patients with recurrent CDI who have not responded to treatment with the regimen used for the first episode of CDI.

CONCLUSION

Fidaxomicin is a well-tolerated agent for the treatment of CDI and has been shown to be noninferior to vancomycin in the management of mild-to-moderately severe CDI.

Fidaxomicin: a macrocyclic antibiotic for the treatment of Clostridium difficile infection

Clostridium difficile is an emerging pathogen in certain health care systems and community-based populations that is associated with high rates of morbidity and mortality, as well as increased costs for the health care system. As recurrence rates increase, new pharmacologic agents to treat C. difficile infection are needed. Fidaxomicin, a novel macrocyclic antibiotic, was recently approved by the United States Food and Drug Administration for the treatment of C. difficile-associated diarrhea. Originally isolated from fermentation broth of Dactylosporangium aurantiacum subspecies hamdenensis, the drug has a selective spectrum, distinctive pharmacokinetic and pharmaco-dynamic properties, and a favorable adverse-effect profile. Fidaxomicin has demonstrated similar clinical cure rates (i.e., resolution of diarrhea) compared with vancomycin, with lower recurrence rates and higher global cure rates (i.e., resolution of diarrhea without recurrence) in non-restriction endonuclease analysis type BI, North American Pulsed Field type 1 (NAP1), polymerase chain reaction ribotype 027 (or non-BI/NAP1/027) strains. Overall, fidaxomicin has been generally well tolerated, with the most common adverse effects reported as mild gastrointestinal complaints. Fidaxomicin appears to be a useful agent in the treatment of severe C. difficile infection, demonstrating decreased rates of recurrence.

Fidaxomicin: first-in-class macrocyclic antibiotic

The incidence of Clostridium difficile has doubled over the past 15 years, and rising mortality rates associated with this infection have followed in its wake. C. difficile infection (CDI) has supplanted methicillin-resistant Staphylococcus aureus as the major cause of nosocomial infection. An insufficient response rate to currently available CDI therapies has prompted the search for new and alternative treatment modalities for this disease. The investigational pipeline includes evaluation of new antimicrobial agents that exhibit good activity against C. difficile without altering normal gut flora, C. difficile toxin-absorbing compounds, and preformed antibodies and vaccines against C. difficile toxin. In two robust clinical trials comparing fidaxomicin to vancomycin in the treatment of CDI, treatment with fidaxomicin demonstrated a superior global cure (cure without recurrence) rate compared with the current gold standard, vancomycin. Fidaxomicin, the first of a new class of macrocyclic antimicrobial agents, represents an advance in the management of CDI.

Fidaxomicin

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