Safety analysis of glecaprevir/pibrentasvir in patients with markers of advanced liver disease in clinical and real-world cohorts.

Chronic hepatitis C virus (HCV) infection has the greatest health impact in patients with advanced liver disease. The direct-acting antiviral (DAA) regimen glecaprevir/pibrentasvir (G/P) is approved for treatment of HCV-infected patients without cirrhosis and with compensated cirrhosis. However, events of liver decompensation/failure have been reported in patients treated with protease-inhibitor-containing DAA regimens, often in patients with advanced liver disease. This study examines the safety of on-label G/P treatment in patients with compensated cirrhosis (F4 at baseline) with markers of advanced liver disease. Patients with cirrhosis were categorized into 4 subgroups, based on different noninvasive markers of advanced liver disease identified using laboratory measures: platelet count < or ≥ 100 × 109 /L, and Child-Pugh score 5 or 6. Separate analyses were performed using pooled data from clinical trials and from real-world post-marketing observational studies. G/P was well tolerated in patients with platelet count ≥100 × 109 /L (n = 800), platelet count <100 × 109 /L (n = 215), a Child-Pugh score of 5 (n = 915) and a Child-Pugh score of 6 (n = 95). In the clinical trial and real-world cohorts two patients and no patients experienced a serious adverse event (AE) possibly related to study drug, respectively; three patients and no patients experienced an AE of special interest for hepatic decompensation and hepatic failure. This analysis reaffirms G/P's safety profile in indicated patients with compensated cirrhosis, including those with markers of more advanced liver disease. Increasing the number of patients treated with short-duration G/P therapy may contribute to meeting HCV elimination targets.

The changing characteristics of patients infected with chronic hepatitis C virus from 2014 to 2019: Real-world data from the German Hepatitis C-Registry (DHC-R).

The number of patients diagnosed with hepatitis C virus (HCV) is markedly higher than the number initiating treatment indicating gaps in the care cascade, likely centred around reaching at-risk populations. Understanding changing characteristics of patients with HCV allows for targeted programs that increase linkage to care. We investigated changes in demographic and clinical characteristics of patients registered in the German Hepatitis C-Registry (DHC-R) from 1 January 2014 to 31 December 2019. The DHC-R is an ongoing, noninterventional, multicentre, prospective, observational cohort registry including 327 German centres. Patient characteristics were analysed over time in 7 phases for all patients completing a screening visit. Overall, 14,357 patients were enrolled. The percentage of treatment-naïve/non-cirrhotic patients increased from 34.4% in phase 1 (1 January-31 December 2014) to 68.2% in phase 7 (1 August-31 December 2019). The proportion of migrants, alcohol users, people who inject drugs, and those receiving opiate substitution therapy increased in later registry phases. Most patients (60.1%) were receiving comedication at baseline. The most prescribed comedications were drugs used to treat opioid dependence which increased from 9.2% in phase 1 to 24.0% in phase 7. The patients' mean age decreased from 52.3 years in phase 1 to 48.7 years in phase 7. From 2014 to 2019, the proportion of at-risk patients enrolling in the registry increased. To eliminate viral hepatitis as a major public health threat, a continued commitment to engaging underserved populations into the HCV care cascade is needed.

Real-World Outcomes in Historically Underserved Patients with Chronic Hepatitis C Infection Treated with Glecaprevir/Pibrentasvir.

INTRODUCTION: Glecaprevir/pibrentasvir is approved for treating chronic hepatitis C virus (HCV) genotypes (GT) 1-6. We evaluated real-world effectiveness, safety, and patient-reported outcomes of glecaprevir/pibrentasvir in underserved patient populations, focusing on persons who use drugs infected with HCV. METHODS: Data were pooled from nine countries (13 November 2017-31 January 2020). Patients had HCV GT1-6, with or without compensated cirrhosis, with or without prior HCV treatment and received glecaprevir/pibrentasvir consistent with local label at their physician's discretion. Patients with prior direct-acting antiviral exposure were excluded from efficacy and quality-of-life analyses. The percentage of patients achieving sustained virologic response at post-treatment week 12 (SVR12) was assessed. Mean changes from baseline to SVR12 visit in 36-Item Short-Form Health Survey mental and physical component summary scores were reported. Safety was assessed in patients receiving at least one dose of glecaprevir/pibrentasvir. RESULTS: Of 2036 patients, 1701 (83.5%) received 8-week glecaprevir/pibrentasvir. In 1684 patients with sufficient follow-up, SVR12 rates were 98.0% (1651/1684) overall, 98.1% (1432/1459) in 8-week treated patients, 97.0% (519/535) in persons who use drugs, and greater than 95% across subgroups. Mean changes from baseline in mental and physical component summary scores were 3.7 and 2.4, respectively. One glecaprevir/pibrentasvir-related serious adverse event was reported; six glecaprevir/pibrentasvir-related adverse events led to discontinuation. CONCLUSIONS: Glecaprevir/pibrentasvir was highly effective, well tolerated, and improved quality of life in HCV-infected persons who use drugs and other underserved patients. TRIAL REGISTRATION: These multinational post-marketing observational studies are registered with ClinicalTrials.gov, number NCT03303599.

Glecaprevir/pibrentasvir for 8 weeks in patients with compensated cirrhosis: Safety and effectiveness data from the German Hepatitis C-Registry.

Glecaprevir/pibrentasvir, a pangenotypic, direct-acting antiviral combination approved for chronic hepatitis C virus treatment, has limited real-world evidence supporting 8-week therapy in compensated cirrhosis. We investigated effectiveness and safety of 187 hepatitis C virus-infected, treatment-naïve, patients with compensated cirrhosis receiving 8-week glecaprevir/pibrentasvir therapy in the German Hepatitis C-Registry between 2 August 2017 and 1 January 2020. Sustained virologic response was 98.4% (127/129) in the per-protocol analysis (excluding patients lost to follow-up or who discontinued treatment due to compliance) and was 85.8% (127/148) in patients with data available in an intention-to-treat analysis. Nineteen patients were lost to follow-up; nine genotype 3 patients, nine nongenotype 3 patients and one mixed genotype patient. One patient relapsed, and one died, unrelated to treatment. Adverse events (>5%) were fatigue and headache. Two serious adverse events occurred; no adverse events resulted in drug discontinuation. An 8-week glecaprevir/pibrentasvir therapy was effective and well-tolerated in this real-world analysis.

Safety of Patients with Hepatitis C Virus Treated with Glecaprevir/Pibrentasvir from Clinical Trials and Real-World Cohorts.

INTRODUCTION: More than 70 million people are estimated to be infected with hepatitis C virus (HCV) globally. If left untreated, HCV infection can lead to complications such as extensive liver fibrosis, cirrhosis, and hepatocellular carcinoma (HCC). Evolution of treatments has resulted in highly effective and well-tolerated all-oral direct-acting antivirals. The pangenotypic regimen of glecaprevir/pibrentasvir is approved for treating HCV for patients without cirrhosis or with compensated cirrhosis (CC). Guidelines have evolved to simplify treatment to enable non-specialists to manage and treat HCV-infected patients. Simultaneously, such treatment algorithms provide guidance on the pretreatment identification of small subsets of patients who may require specialist treatment and long-term follow-up for advanced liver disease, including those at risk of developing HCC. This study describes the safety profile of glecaprevir/pibrentasvir in patients identified using previously described noninvasive laboratory measures who may be eligible for treatment by non-liver specialists. METHODS: This post hoc analysis of glecaprevir/pibrentasvir in patients, identified by noninvasive laboratory measures, intended to exclude patients with advanced liver disease and severe renal impairment, who can be managed within non-liver specialist settings. Patients were included from clinical trials and real-world studies of glecaprevir/pibrentasvir for HCV treatment. Baseline demographics, clinical characteristics, and safety assessments, including adverse events and laboratory abnormalities, were summarized. RESULTS: Data across these large-scale studies confirm that glecaprevir/pibrentasvir is well tolerated across different patient populations, with fewer than 0.1% of patients experiencing a serious adverse event related to treatment drugs, and few patients developing HCC during or after treatment. CONCLUSION: The safety profile of glecaprevir/pibrentasvir enhances the confidence of non-liver specialists to treat the majority of HCV-infected patients, and provides an opportunity to expand the treater pool, potentially increasing diagnosis and treatment rates for HCV, contributing to elimination of HCV.

Addressing HCV Elimination Barriers in Italy: Healthcare Resource Utilization and Cost Impact Using 8 Weeks' Glecaprevir/Pibrentasvir Therapy.

INTRODUCTION: In Italy, hepatitis C virus (HCV) elimination is achievable; however, barriers remain to achieving the World Health Organization's elimination targets, and have become more pronounced with the spread of COVID-19. Glecaprevir/pibrentasvir (G/P) is a direct-acting antiviral therapy for HCV, approved for 8-week treatment in patients without cirrhosis, and with compensated cirrhosis (CC). Previously, 12 weeks of therapy was recommended for patients with CC. Shortened treatment may reduce the burden on healthcare resources, allowing more patients to be treated. This study presents the benefits that 8-week vs 12-week treatment with G/P may have in Italy. METHODS: A multicohort Markov model was used to assess the collective number of healthcare visits and time on treatment with 8-week vs 12-week G/P in the HCV-infected population of Italy from 2019 to 2030, using healthcare resource data from post-marketing observational studies of G/P. Increased treatment capacity and downstream clinical and economic benefits were also assessed assuming the reallocation of saved healthcare visits to treat more patients. RESULTS: Modeled outcomes showed that by 2030, 8-week treatment saved 27,006 years on therapy compared with 12-week treatment, with 21,065 fewer hepatologist visits. Reallocating these resources to treat more patients could increase capacity to treat 5064 (1.4%) more patients with 8 weeks of G/P, all with CC. This increased treatment capacity would further avoid 2257 cases of end-stage liver disease, 893 liver-related deaths, and provide net savings to the healthcare system of nearly €70 million. CONCLUSION: The modeled comparisons between 8- and 12-week treatment with G/P show that shorter treatment duration can lead to greater time and resource savings, both in terms of healthcare visits and downstream costs. These benefits have the potential to enable the treatment of more patients to overcome elimination barriers in Italy through programs aimed to engage and treat targeted HCV populations.

Correction to: Real-World Clinical Practice Use of 8-Week Glecaprevir/Pibrentasvir in Treatment-Naïve Patients with Compensated Cirrhosis.

In the original article, there is an error in Fig. 1.

Real-World Clinical Practice Use of 8-Week Glecaprevir/Pibrentasvir in Treatment-Naïve Patients with Compensated Cirrhosis.

INTRODUCTION: More than 70 million people are estimated to be infected with hepatitis C virus globally. Glecaprevir/pibrentasvir is a widely used treatment and has recently been approved for an 8-week regimen for treatment-naïve patients with compensated cirrhosis in Europe and the USA, who would previously have received glecaprevir/pibrentasvir for 12 weeks. This label update was based on the EXPEDITION-8 study, which included 343 treatment-naïve patients with compensated cirrhosis. However, there is currently a lack of similarly large-scale real-world studies of the 8-week glecaprevir/pibrentasvir regimen in this population. METHODS: This summary of seven separate smaller real-world studies aims to validate the results seen in EXPEDITION-8 and provide an up-to-date real-world reference for clinicians making treatment decisions for patients with compensated cirrhosis (Child-Pugh A) who may benefit from a shorter-duration therapy with glecaprevir/pibrentasvir. The newly emerging real-world effectiveness data on treatment-naïve patients with compensated cirrhosis treated with 8 weeks of glecaprevir/pibrentasvir help to understand where further research is needed to support patients with hepatitis C virus. RESULTS: Across all seven studies, glecaprevir/pibrentasvir showed high effectiveness with an average sustained virologic response rate of 98.1%, similar to that found in a clinical trial setting (99.7%). Only one patient (0.5%) experienced virologic failure and treatment was well tolerated. CONCLUSION: Expanding the number of patients eligible for the shortened treatment duration will potentially increase treatment initiation and completion, particularly in underserved populations, contributing to the elimination of hepatitis C virus.

Long-term safety and efficacy results in hepatitis C virus genotype 1-infected patients receiving ombitasvir/paritaprevir/ritonavir + dasabuvir ± ribavirin in the TOPAZ-I and TOPAZ-II trials.

The 3-DAA regimen consisting of ombitasvir/paritaprevir/ritonavir plus dasabuvir (OBV/PTV/r + DSV) ± ribavirin (RBV) has shown high sustained virologic response rates (~95%) in phase 3 clinical trials including >2300 HCV genotype 1-infected patients. Real-world evidence studies have confirmed the effectiveness of OBV/PTV/r ± DSV ± RBV in patients with chronic HCV genotype 1 infection and are consistent with clinical trial results. TOPAZ-I and TOPAZ-II are ongoing phase 3b trials, assessing safety, efficacy and long-term progression of liver disease and clinical outcomes for up to 5 years post-treatment in patients treated with OBV/PTV/r + DSV ± RBV. High rates of sustained virologic response (SVR) were achieved regardless of presence or absence of cirrhosis.In this report, we assessed the long-term progression of liver disease and incidence of clinical outcomes up to 3 years of post-treatment follow-up in patients with chronic HCV GT1 infection who were treated with (OBV/PTV/r + DSV) ± RBV in the TOPAZ-I and TOPAZ-II studies. Improvements were observed in liver disease markers including FIB-4, METAVIR and Child-Pugh scores as well as platelet counts. Clinical outcomes related to long-term progression of liver disease such as liver decompensation were infrequent (<1%). Hepatocellular carcinoma (HCC) occurred in 1.4% of cirrhotic patients.

Efficacy and Safety of 8 Weeks of Glecaprevir/Pibrentasvir in Treatment-Naïve, HCV-Infected Patients with APRI ≤ 1 in a Single-Arm, Open-Label, Multicenter Study.

INTRODUCTION: The presence or absence of cirrhosis in patients with chronic hepatitis C virus (HCV) infection influences the type and duration of antiviral therapy. Non-invasive markers, like serum aspartate aminotransferase (AST) to platelet ratio index (APRI), may help identify appropriate HCV treatment-naive patients for 8-week treatment with the pangenotypic regimen of glecaprevir/pibrentasvir. METHODS: This single-arm, open-label, international, prospective study (NCT03212521) evaluated the efficacy and safety of 8-week glecaprevir/pibrentasvir regimen in HCV treatment-naïve adults with chronic HCV genotypes 1-6 infection, APRI ≤ 1, and no prior evidence of cirrhosis. The primary and secondary outcomes were sustained virologic response at 12 weeks post-treatment (SVR12) by modified intent-to-treat (mITT) and intent-to-treat (ITT) analyses, respectively. Additional endpoints included virologic failures, treatment adherence, and genotype-specific SVR12 rates. RESULTS: Among the 230 patients enrolled, most were less than 65 years old (90%); 37% and 43% had a history of injection drug use or psychiatric disorders, respectively. SVR12 rates were 100% (222/222; 95% CI 98.3-100%) and 96.5% (222/230; 95% CI 94.2-98.9%) by mITT and ITT analyses, respectively. There were no virologic failures. ITT SVR12 rates were greater than 94% for all HCV genotypes. In patients with available data, treatment adherence was 99% (202/204). There were no grade 3 or higher laboratory abnormalities in alanine aminotransferase (ALT), aspartate aminotransferase (AST), and total bilirubin, and low rates of serious adverse events (2%). CONCLUSIONS: Glecaprevir/pibrentasvir was highly efficacious and well tolerated in HCV treatment-naïve patients with APRI ≤ 1 and no prior evidence of cirrhosis. TRIAL REGISTRATION: ClinicalTrials.gov number, NCT03212521. FUNDING: AbbVie. Plain language summary available for this article.

Efficacy and safety of glecaprevir/pibrentasvir in patients with chronic HCV infection and psychiatric disorders: An integrated analysis.

Although direct-acting antivirals (DAAs) for chronic hepatitis C virus (HCV) infection are highly efficacious and safe, treatment initiation is often limited in patients with neuropsychiatric disorders due to concerns over reduced treatment adherence and drug-drug interactions. Here, we report adherence, efficacy, safety and patient-reported outcomes (PROs) from an integrated analysis of registrational studies using the pangenotypic DAA regimen of glecaprevir and pibrentasvir (G/P). Patients with chronic HCV genotypes 1-6 infection with compensated liver disease (with or without cirrhosis) receiving G/P for 8, 12 or 16 weeks were included in this analysis. Patients were classified as having a psychiatric disorder based on medical history and/or co-medications. Primary analyses assessed treatment adherence, efficacy (sustained virologic response at post-treatment week 12; SVR12), safety and PROs. Among 2522 patients receiving G/P, 789 (31%) had a psychiatric disorder with the most common diagnoses being depression (64%; 506/789) and anxiety disorders (27%; 216/789). Treatment adherence was comparably high (>95%) in patients with and without psychiatric disorders. SVR12 rates were 97.3% (768/789; 95% CI = 96.2-98.5) and 97.5% (1689/1733; 95% CI = 96.7-98.2) in patients with and without psychiatric disorders, respectively. Among patients with psychiatric disorders, SVR12 rates remained >96% by individual psychiatric diagnoses and co-medication classes. Overall, most adverse events (AEs) were mild-to-moderate in severity with serious AEs and AEs leading to G/P discontinuation occurring at similarly low rates in both patient populations. In conclusion, G/P treatment was highly efficacious, well-tolerated and demonstrated high adherence rates in patients with chronic HCV infection and psychiatric disorders.

Real-world safety and effectiveness of ombitasvir/paritaprevir/ritonavir ± dasabuvir ± ribavirin in hepatitis C virus genotype 1- and 4-infected patients with diverse comorbidities and comedications: A pooled analysis of post-marketing observational studies from 13 countries.

Ombitasvir/paritaprevir/ritonavir ± dasabuvir ± ribavirin (OBV/PTV/r ± DSV ± RBV) regimens show high efficacy and good tolerability in clinical trials for chronic hepatitis C virus (HCV) genotypes (GT) 1 or 4. To evaluate whether these results translate to clinical practice, data were pooled from observational studies across 13 countries. Treatment-naïve or -experienced patients, with or without cirrhosis, received OBV/PTV/r ± DSV ± RBV according to approved local labels and clinical practice. Sustained virologic response at post-treatment Week 12 (SVR12), adverse events (AEs) and comedication management were assessed for patients initiating treatment before 1 June 2017. The safety population included 3850 patients who received ≥1 dose of study drug. The core population (N = 3808) further excluded patients with unknown GT or cirrhosis status, or who received off-label treatment. Patients had HCV GT1a (n = 732; 19%), GT1b (n = 2619; 69%) or GT4 (n = 457; 12%). In 3546 patients with sufficient follow-up data at post-treatment Week 12, the SVR12 rate was 96% (n/N = 3401/3546 [95% CI 95.2-96.5]). In patients with or without cirrhosis, SVR12 was comparable (96%). In patients with HCV GT1a, GT1b or GT4, SVR12 rates were 93%, 97% and 94%. In GT1b-infected patients with planned treatment for 8 weeks, SVR12 was 96%. In patients with ≥1 comorbidity (67%), SVR12 was 95%. 58% of patients received ≥1 comedication, and there was minimal impact on SVR12 rates using comedications for peptic ulcers and gastro-esophageal reflux disease, statins, antipsychotics or antiepileptics. Most comedications were maintained during treatment although 58% of patients changed their statin medication. AEs and serious AEs occurred in 26% and 3% of patients. Post-baseline Grade 3-4 laboratory abnormalities were rare (<3%), and discontinuation rates were low (<4%). Real-world evidence confirms the effectiveness of OBV/PTV/r ± DSV ± RBV in patients with HCV GT1 or GT4, regardless of common comorbidities or comedications, and is consistent with clinical trial results. Adverse safety outcomes may be limited by underreporting in the real-world setting.

Expert opinion on managing chronic HCV in patients with neuropsychiatric manifestations.

Neurological manifestations of HCV infection appear to be under-recognized in clinical practice despite the majority of HCV-infected patients experiencing symptoms such as fatigue, depression and cognitive dysfunction. There is also growing evidence for a link between HCV infection and an increased risk of Parkinson's disease. The mechanism underpinning the association between HCV and these neuropsychiatric syndromes still requires further investigation. Here we review the pre-clinical and clinical evidence for a link between HCV and effects on the central nervous system leading to neuropsychiatric syndromes. Lastly, we describe how improvements in neuropsychiatric manifestations of HCV following treatment have been observed, which is subsequently reflected in an overall improvement in health-related quality of life.

Expert opinion on managing chronic HCV in patients with non-Hodgkin lymphoma and other extrahepatic malignancies.

HCV is a carcinogen that is well established as a major risk factor for hepatocellular carcinoma. Evidence that HCV plays a role in the development of extrahepatic malignancies is less robust; however, epidemiological studies have consistently demonstrated an association between HCV infection and B-cell non-Hodgkin lymphoma (NHL). The strongest evidence for a link between HCV and tumourigenesis is the clear association between viral eradication, as indicated by achievement of sustained virological response, and remission of B-cell NHL. All-oral direct-acting antiviral-based therapies are effective in patients with HCV-associated NHL and well tolerated. For this reason, it is important that clinicians assess HCV-infected patients for HCV-associated extrahepatic malignancies so patients can receive timely diagnosis and treatment.

Expert opinion on managing chronic HCV in patients with mixed cryoglobulinaemia vasculitis.

Mixed cryoglobulinaemia vasculitis (CryoVas) is a small-vessel systemic vasculitis caused by deposition of mixed cryoglobulins and is characterized by a wide range of clinical symptoms. HCV is the primary cause of CryoVas, which is associated with significant morbidity and mortality. The mortality rate among patients with HCV-associated CryoVas is 3× that of the general population, with a 63% 10-year survival rate. First-line treatment for CryoVas is anti-HCV therapy because viral clearance is associated with clinical improvement. The introduction of highly effective, interferon-free, direct-acting antiviral regimens provides additional treatment options for these patients. Here, we review recent studies investigating the effect of antiviral therapy on HCV-associated CryoVas and provide expert opinion for health-care professionals managing these patients.

Expert opinion on managing chronic HCV in patients with cardiovascular disease.

Extrahepatic manifestations of chronic HCV infection include cardiovascular diseases and an increase in cardiovascular mortality. The pathogenic mechanisms by which HCV contributes to cardiovascular disease are not well defined, however, it is likely that systemic inflammation, and the promotion of other metabolic diseases are involved. In this Review, the evidence for HCV infection as a non-traditional risk factor for cardiovascular disease is evaluated. Furthermore, practical advice to evaluate cardiovascular disease risk and disease in chronic hepatitis C patients are included for help in daily clinical practice. Despite the advances in therapies for the treatment of HCV, there remains a need for increased awareness among specialists so that patients are more likely to obtain the treatment required to mitigate disease progression.

Expert opinion on the management of renal manifestations of chronic HCV infection.

Chronic HCV infection is a non-traditional (but modifiable) risk factor for chronic kidney disease and has been implicated in glomerular injury and nephrosclerotic disease. Three HCV direct-acting antiviral regimens are available for patients with severe kidney impairment: ombitasvir, paritaprevir with the pharmacokinetic enhancer ritonavir, and dasabuvir; glecaprevir plus pibrentasvir; and elbasvir plus grazoprevir. In patients with severe kidney impairment, sofosbuvir-free regimens are preferred because sofosbuvir accumulation has been associated with a progressive worsening of renal function. In this Review, we provide our expert opinion on the current HCV treatment paradigm and highlight the remaining issues that need to be overcome to improve the treatment of HCV in this population.

Expert opinion on managing chronic HCV infection in patients with type 2 diabetes mellitus.

Type 2 diabetes mellitus (T2DM) has been identified as an extrahepatic manifestation of chronic HCV infection. Conversely, in the context of chronic HCV infection, T2DM can accelerate the course of HCV-induced liver disease leading to increased risk of fibrosis, cirrhosis and hepatocellular carcinoma. The presence of T2DM negatively impacts the efficacy of interferon-based antiviral therapy, but real-world data with high-efficacy direct-acting antiviral therapies suggest high viral clearance rates in T2DM patients. In HCV-infected individuals, viral eradication is associated with a reduced risk of de novo T2DM in non-diabetic patients and beneficial metabolic changes in patients with T2DM, highlighting the importance of antiviral treatment and physician awareness of this association.

Electrocatalytic proton reduction by phosphido-bridged diiron carbonyl compounds: distant relations to the H-cluster?

Intermediates formed during reduction of Fe(2)(mu-PPh(2))(2)(CO)(6) (1) in the presence of protons have been identified by spectroelectrochemical, continuous-flow, and interrupted-flow techniques. The mechanism for electrocatalytic proton reduction suggested by these observations yields digital simulation of the voltammetry in close agreement with measurements conducted in THF over a range of acid concentrations. The mechanism for electrocatalytic proton reduction involves initial formation of the dianion, 1(2-), which is doubly protonated prior to further reduction and dihydrogen elimination. The IR spectra of the singly and doubly protonated forms of 1(2-) indicate structures corresponding to [FeH(CO)(3)(mu-PPh(2))(2)Fe(CO)(3)](-) (1H-) and FeH(CO)(3)(mu-PPh(2))(2)FeH(CO)(3) (1H(2)). The thiolato and dithiolato analogues of 1 exhibit electrocatalytic proton reduction associated with the two-electron reduction step, and this implies that the corresponding two-electron reduced doubly protonated species is unstable with respect to dihydrogen elimination. The stability of 1H(2) is most likely to be due to the weak interactions between the iron centers of the flattened [2Fe2P] core. Whereas 1H(2) is stable in the absence of a reducing potential, 1H- rearranges rapidly to a product previously described as [Fe(2)(mu-PPh(2))(mu-CO)(PHPh(2))(CO)(5)](-) (1H-(W)). Another protonation product of 1(2-), previously formulated as [Fe(2)(mu-PPh(2))(2)(mu-CO)H(CO)(5)](-), has been reformulated as [Fe(2)(mu-PPh(2))(mu-CO)(CO)(6)](-) (2) on the basis of a range of spectroscopic measurements. Solution EXAFS measurements of 1, 1(2-), 1H-(W), and 2 are reported, and these yield model-independent Fe-Fe distances of 2.61 (1), 3.58 (1(2-)), 2.58 (1H-(W)), and 2.59 A (2). The presence of an Fe-Fe bond for both 1H-(W) and 2 is a key aspect of the proposed structures, and this strongly supports the deductions based on spectroscopic evidence. The fits of the solution EXAFS to different structural models give statistics in agreement with the proposed structures.