Resistant Hypertension: Disease Burden and Emerging Treatment Options

PURPOSE OF REVIEW

To define resistant hypertension (RHT), review its pathophysiology and disease burden, identify barriers to effective hypertension management, and to highlight emerging treatment options.

RECENT FINDINGS

RHT is defined as uncontrolled blood pressure (BP) ≥ 130/80 mm Hg despite concurrent prescription of ≥ 3 or ≥ 4 antihypertensive drugs in different classes or controlled BP despite prescription of  ≥ to 4 drugs, at maximally tolerated doses, including a diuretic. BP is regulated by a complex interplay between the renin-angiotensin-aldosterone system, the sympathetic nervous system, the endothelin system, natriuretic peptides, the arterial vasculature, and the immune system; disruption of any of these can increase BP. RHT is disproportionately manifest in African Americans, older patients, and those with diabetes and/or chronic kidney disease (CKD). Amongst drug-treated hypertensives, only one-quarter have been treated intensively enough (prescribed > 2 drugs) to be considered for this diagnosis. New treatment strategies aimed at novel therapeutic targets include inhibition of sodium-glucose cotransporter 2, aminopeptidase A, aldosterone synthesis, phosphodiesterase 5, xanthine oxidase, and dopamine beta-hydroxylase, as well as soluble guanylate cyclase stimulation, nonsteroidal mineralocorticoid receptor antagonism, and dual endothelin receptor antagonism. The burden of RHT remains high. Better use of currently approved therapies and integrating emerging therapies are welcome additions to the therapeutic armamentarium for addressing needs in high-risk aTRH patients.

Updated Renal Dosage Recommendations for Rivaroxaban in Patients Experiencing or at Risk of Thromboembolic Disease

Patients with chronic kidney disease are at an increased risk of venous thromboembolism (VTE). The factor Xa inhibitor rivaroxaban has been shown to provide similar efficacy and a lower risk of bleeding compared with vitamin K antagonists for the treatment and prevention of VTE. Rivaroxaban has been studied in patients with varying degrees of renal impairment, and this review summarizes current knowledge supporting its use in patients with severe renal impairment (creatinine clearance [CrCl] of 15 to < 30 mL/min) for the prevention, treatment, or prophylaxis of VTE. Clinical pharmacology studies have demonstrated an increase in rivaroxaban systemic exposure, factor Xa inhibition, and prothrombin time with decreasing renal function. These changes reach a plateau with comparable increases in exposure among individuals with moderate or severe renal impairment and end-stage renal disease. The clinical development program for the treatment and prevention of VTE as well as prophylaxis of deep vein thrombosis (DVT) following orthopedic surgery excluded patients with CrCl < 30 mL/min; however, a limited number of patients with severe renal impairment were enrolled. Efficacy outcomes in these patients with severe renal impairment were not meaningfully different from those of patients with higher levels of renal function. There was also no increase in the incidence of major bleeding with rivaroxaban in patients with CrCl < 30 mL/min. Taken together, these pharmacological and clinical data suggest that in patients with severe renal impairment, the approved dosages of rivaroxaban can be used in the treatment and prevention of VTE and for prophylaxis of DVT after hip or knee replacement surgery.

Effectiveness, safety, and healthcare costs associated with rivaroxaban versus warfarin among venous thromboembolism patients with obesity: a real-world study in the United States

Prior observational studies suggest rivaroxaban is safe and effective among patients with morbid obesity who suffered a venous thromboembolism (VTE) event, but existing data are more limited in the broader population of VTE patients with obesity. This study assessed VTE recurrence, major bleeding, healthcare resource utilization, and healthcare costs among VTE patients with obesity who received rivaroxaban versus warfarin. VTE patients with obesity who initiated rivaroxaban or warfarin after a first VTE (index date) were identified from the IQVIA PharMetrics® Plus database (01/02/2011–09/30/2019). The follow-up period spanned from the index date until health plan disenrollment, end of data availability, cancer diagnosis/treatment, end of the 12 month post-index period, or (for the analysis of major bleeding) anticoagulant discontinuation or switch. Patient characteristics were balanced using inverse probability of treatment weighting. The weighted rivaroxaban (N = 8666) and warfarin cohorts (N = 5946) were well balanced (mean age = 51 years, females = 52%). Over a 9.6 months mean observation period, rivaroxaban users had a significantly lower risk of VTE recurrence [7.0% vs. 8.2%, HR(95% CI) = 0.85(0.75;0.97)] and a similar risk of major bleeding [4.1% vs. 3.6%, HR(95% CI) = 1.11(0.89;1.37)] relative to warfarin users at 12 months. Relative to warfarin users, rivaroxaban users had significantly fewer all-cause outpatient visits [RR(95% CI) = 0.71(0.70;0.74)]. The higher pharmacy costs incurred by rivaroxaban recipients (cost difference = $1252) were offset by lower medical costs (cost difference = − $2515, all p < 0.05) compared with warfarin recipients. Our findings suggest that rivaroxaban is safe and effective versus warfarin, and associated with lower medical costs among VTE patients with obesity.

Biomarker signatures in cancer patients with and without venous thromboembolism events: a substudy of CASSINI

Cancer is associated with an increased risk of venous thromboembolism (VTE). In the CASSINI study, ambulatory cancer patients with a Khorana risk score ≥2 had a reduced risk of VTE while receiving rivaroxaban. This analysis used blood samples from CASSINI to compare biomarker levels between patients with and without VTE. VTE occurred in 62 patients during the 6 months of CASSINI (cases), and they were matched by age, sex, cancer type, tumor stage, and Khorana score to 62 controls. Baseline blood samples were analyzed for 280 biomarkers, and biomarker distribution was compared using the Wilcoxon rank-sum test between groups defined by VTE occurrence and vital status. Sparse Bayesian regression modeling was used to select a joint panel of potential VTE biomarkers. Biomarkers with the largest differences in baseline distribution among cancer patients with and without VTE included decreases in stromal cell-derived factor-1 (SDF-1), thyroid-stimulating hormone (TSH), and monocyte chemotactic protein 4 and increases in growth hormone (GH) and interleukin-1 receptor type 1 (IL-1R1). Between survivors and those who died, significantly different biomarkers included ST2, IL-8, and C-reactive protein. Regression analyses also identified decreases in SDF-1 and TSH. Pathway analysis indicated enrichment of cytokine and chemokine activity with IL-1R1, SDF-1, and GH, which are the strongest predictors of VTE or death. Our analyses highlight the interactions between hemostatic and inflammatory processes and identify candidate biomarkers of cancer-associated VTE. Prospective studies will determine clinical relevance of these biomarkers. This trial was registered at www.ClinicalTrials.gov as #NCT02555878.

Economic burden of rivaroxaban and warfarin among nonvalvular atrial fibrillation patients with obesity and polypharmacy

Aim: Evaluate healthcare resource utilization (HRU) and costs associated with rivaroxaban and warfarin among nonvalvular atrial fibrillation (NVAF) patients with obesity and polypharmacy. Materials & methods: IQVIA PharMetrics^® Plus (January 2010-September 2019) data were used to identify NVAF patients with obesity (BMI ≥30 kg/m²) and polypharmacy (≥5 medications) initiated on rivaroxaban or warfarin. Weighted rate ratios and cost differences were evaluated post-treatment initiation. Results: Rivaroxaban was associated with significantly lower rates of HRU, including hospitalization (rate ratio [95% CI]: 0.83 [0.77, 0.92]). Medical costs were reduced in rivaroxaban users (difference [95% CI]: -US$6868 [-US$10,628, -US$2954]), resulting in significantly lower total healthcare costs compared with warfarin users (difference [95% CI]: -US$4433 [-US$8136, -US$582]). Conclusion: Rivaroxaban was associated with lower HRU and costs compared with warfarin among NVAF patients with obesity and polypharmacy in commercially insured US patients.

Comparative Effectiveness and Safety of Rivaroxaban and Warfarin Among Nonvalvular Atrial Fibrillation (NVAF) Patients with Obesity and Polypharmacy in the United States (US)

Introduction

Current evidence indicates that rivaroxaban may be a safe and effective alternative to warfarin among patients with nonvalvular atrial fibrillation (NVAF) and obesity. However, evidence regarding the impact of polypharmacy is limited in this population. The present study evaluated the effectiveness and safety of rivaroxaban versus warfarin among NVAF patients with obesity and polypharmacy in the US.

Methods

De-identified health insurance claims data from the IQVIA PharMetrics^® Plus data (01/2010–09/2019) were used to identify NVAF patients with obesity (BMI ≥ 30 kg/m²) and polypharmacy (≥ 5 medications) initiated on rivaroxaban or warfarin. Inverse probability of treatment weighting (IPTW) was used to adjust for imbalances between groups. Study outcomes were evaluated up to 36 months post-treatment initiation and included the composite of stroke or systemic embolism (stroke/SE) and major bleeding. Subgroup analyses were conducted stratified by polypharmacy category (5–9 or ≥ 10 medications). Outcomes were assessed using Cox proportional hazards regression models with hazard ratios (HR) and 95% confidence intervals (CIs).

Results

A total of 7000 and 3920 NVAF patients with obesity and polypharmacy were initiated on rivaroxaban and warfarin, respectively. At 36 months of follow-up, rivaroxaban was associated with a 29% lower risk of stroke/SE relative to warfarin (HR 0.71, 95% CI 0.57, 0.90). Major bleeding risk was not significantly different among rivaroxaban- compared to warfarin-treated patients (HR 0.85, 95% CI 0.70, 1.03). Subgroup analyses yielded results that were largely consistent with the overall polypharmacy analysis.

Conclusions

These results suggest that rivaroxaban is an effective and safe treatment option among NVAF patients with obesity and polypharmacy in a commercially-insured US population.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12325-021-01746-2.

Real-world effectiveness and safety of rivaroxaban versus warfarin among non-valvular atrial fibrillation patients with obesity in a US population

OBJECTIVES

Current evidence indicates that the pharmacokinetic profile of rivaroxaban is not significantly impacted by body weight. However, real-world data are needed to better assess the potential clinical benefits and risks associated with rivaroxaban in non-valvular atrial fibrillation (NVAF) patients with obesity. Thus, our objectives were to assess the real-world effectiveness and safety of rivaroxaban versus warfarin among NVAF patients with obesity in the US nationally representative commercially-insured population.

METHODS

Health insurance claims data from the IQVIA PharMetrics Plus database (January 2010-September 2019) were used to identify NVAF patients with obesity (based on diagnosis codes) initiated on rivaroxaban or warfarin. Inverse probability of treatment weighting (IPTW) was used to adjust for imbalances between groups. Study outcomes of interest were evaluated up to 36 months post-treatment initiation and included the composite of stroke or systemic embolism (stroke/SE) and major bleeding. Outcomes were compared using Cox proportional hazards regression models with hazard ratios (HR) and 95% confidence intervals (CIs).

RESULTS

A total of 10,555 patients were initiated on rivaroxaban and 5080 patients on warfarin. Following IPTW, the risk of stroke/SE was 26% lower among patients prescribed rivaroxaban relative to warfarin (HR: 0.74, 95% CI: 0.60, 0.91, p = .004) at 36 months. Rivaroxaban-initiated patients had a risk of major bleeding similar to that of warfarin-initiated patients (HR: 0.85, 95% CI: 0.71, 1.02, p = .085).

CONCLUSIONS

These results suggest that rivaroxaban is an effective and safe treatment option among NVAF patients with obesity in a commercially-insured US population.

Healthcare resource utilization and costs of rivaroxaban versus warfarin among non-valvular atrial fibrillation (NVAF) patients with obesity in a US population

AIM

To assess the real-world healthcare resource utilization (HRU) and costs of patients with non-valvular atrial fibrillation (NVAF) and obesity newly initiated on rivaroxaban or warfarin in the US.

METHODS

This retrospective study used IQVIA PharMetrics Plus data (01/2010-09/2019) to evaluate patients (≥18 years) with NVAF and obesity (body mass index ≥30 kg/m²) initiated on rivaroxaban or warfarin (on or after 01/2013). Inverse probability of treatment weighting (IPTW) was used to adjust for confounding between cohorts. HRU and costs were assessed post-treatment initiation. Weighted cohorts were compared using Poisson regression models and cost differences, with 95% confidence intervals (CIs) and p values generated using non-parametric bootstrap procedures.

RESULTS

After IPTW, 10,555 and 5,080 patients were initiated on rivaroxaban and warfarin, respectively (mean age: 59 years). At 12 months follow-up, the rivaroxaban cohort had lower all-cause HRU, including fewer hospitalizations (rate ratio [RR]: 0.80, 95% CI: 0.74, 0.87), emergency room visits (RR: 0.89, 95% CI: 0.83, 0.97), and outpatient visits (RR: 0.72, 95% CI: 0.69, 0.77; all p < .05). Medical costs were also reduced in the rivaroxaban cohort (mean difference: -$6,759, 95% CI: -$9,814, -$3,311) due to reduced hospitalization costs (mean difference: -$5,967, 95% CI: -$8,721, -$3,327), resulting in lower total all-cause healthcare costs compared to the warfarin cohort (mean difference: -$4,579, 95% CI: -$7,609, -$1,052; all p < .05). The rivaroxaban cohort also had lower NVAF-related HRU and medical costs driven by lower hospitalization at 12 months post-treatment initiation. HRU and cost reductions associated with rivaroxaban persisted up to 36 months of follow-up.

LIMITATIONS

Claims data may have contained inaccuracies and obesity was classified based on ICD diagnosis codes given that patient BMI values were not available.

CONCLUSIONS

Rivaroxaban was associated with reduced HRU and costs compared to warfarin among NVAF patients with obesity in a real-world US setting.

Rivaroxaban Versus Warfarin for Management of Obese African Americans With Non-Valvular Atrial Fibrillation or Venous Thromboembolism: A Retrospective Cohort Analysis

African Americans (AAs) and obese individuals have increased thrombotic risk. This study evaluated the effectiveness and safety of rivaroxaban versus warfarin in obese, AAs with nonvalvular atrial fibrillation (NVAF) or venous thromboembolism (VTE). Optum® De-Identified Electronic Health Record (EHR) data was used to perform separate propensity-score matched analyses of adult, oral anticoagulant (OAC)-naïve AAs with NVAF or acute VTE, respectively; who had a body mass index≥30kg/m² and ≥12-months EHR activity with ≥1-encounter before OAC initiation. Cox regression was performed and reported as hazard ratios (HRs) with 95% confidence intervals (CIs). For the NVAF analysis, 1,969 rivaroxaban- and 1,969 warfarin-users were matched. Rivaroxaban was not associated with a difference in stroke/systemic embolism versus warfarin (HR = 0.88, 95%CI = 0.60-1.28), but less major bleeding (HR = 0.68, 95%CI = 0.50-0.94) was observed. Among 683 rivaroxaban-users with VTE, 1:1 matched to warfarin-users, rivaroxaban did not alter recurrent VTE (HR = 1.36, 95%CI = 0.79-2.34) or major bleeding (HR = 0.80, 95%CI = 0.37-1.71) risk versus warfarin at 6-months (similar findings observed at 3- and 12-months). Rivaroxaban appeared to be associated with similar thrombotic, and similar or lower major bleeding risk versus warfarin in these obese, AA cohorts.

Effectiveness and safety of rivaroxaban versus warfarin in obese nonvalvular atrial fibrillation patients: analysis of electronic health record data

Background: Although rivaroxaban has demonstrated consistent drug levels in normal weight and obese patients, sufficient confirmation of equal clinical effectiveness and safety is currently lacking.Purpose: To evaluate the effectiveness and safety of rivaroxaban versus warfarin for prevention of stroke and systemic embolism (SSE) in obese nonvalvular atrial fibrillation (NVAF) patients.Methods: Using Optum de-identified Electronic Health Record (EHR) data from November 2011 to September 2018,we evaluated NVAF patients with a body mass index (BMI)≥30 kg/m² newly initiated on rivaroxaban or warfarin (index date), with ≥12-months of EHR activity and ≥1 encounter before the index date. We excluded patients with valvular disease or evidence of oral anticoagulant (OAC) use at baseline. Patients who were prescribed rivaroxaban were 1:1 propensity-score matched to patients who were prescribed warfarin (standard differences <0.10 achieved for all covariates). Outcomes included SSE and major bleeding using an intent-to-treat approach. Subanalyses stratified by BMI (30.0-34.9, 35.0-39.9 and ≥40 kg/m²) were performed. Cox regression was performed and reported as hazard ratios (HRs) and 95% confidence intervals (CIs).Results: We included 35,613 rivaroxaban and 35,613 warfarin users with NVAF. Patients were followed for a median of 2.6 years (25%-75% range = 1.2-4.1). Rivaroxaban was associated with a reduced risk of SSE (HR = 0.83, 95%CI = 0.73-0.94) and major bleeding (HR = 0.82, 95%CI = 0.75-0.89) compared to warfarin. Subanalysis did not show a statistically significant interaction across BMI categories for SSE (p-interaction = .58) or major bleeding (p-interaction = .44) outcomes.Conclusions: Among obese NVAF patients, prescription of rivaroxaban was associated with a reduced risk of SSE and major bleeding compared to warfarin, which remained consistent across BMI classes.

Effectiveness and safety of rivaroxaban versus warfarin in obese patients with acute venous thromboembolism: analysis of electronic health record data

There is limited data evaluating clinical outcomes of rivaroxaban versus warfarin in obese patients with venous thromboembolism (VTE). Our objective was to evaluate the effectiveness and safety of rivaroxaban versus warfarin in obese VTE patients. We performed a cohort analysis using Optum® De-Identified Electronic Health Record data from 11/1/2012 to 9/30/2018. Patients with a body mass index (BMI) ≥ 30 kg/m² admitted to the hospital, emergency department or observation unit for VTE, prescribed rivaroxaban or warfarin as their first oral anticoagulant (OAC) within 7-days and had ≥12-months of EHR activity prior were included. We excluded patients with OAC use at baseline or cancer. Patients were 1:1 matched (standard differences<0.10). Primary outcomes were recurrent VTE and major bleeding at 3-, 6- and 12-months using an intent-to-treat approach. Subanalyses of BMI 30.0-34.9, 35.0-39.9 and ≥ 40 kg/m² were performed. Risk was compared using Cox regression and reported as hazard ratios (HRs) with 95% confidence intervals (CI). We identified 6755 rivaroxaban and 6755 warfarin users with BMI ≥ 30 kg/m² and incident VTE. At 3-, 6- and 12-months, rivaroxaban was associated with a reduced hazard of recurrent VTE compared to warfarin (HR 0.61, 95%CI   0.51-0.72; HR 0.65, 95%CI  0.55-0.77; HR 0.63, 95%CI  0.54-0.74) with no difference in major bleeding (HR  0.99, 95%CI  0.68-1.44; HR 0.90, 95%CI  0.64-1.26; HR 1.00, 95%CI  0.73-1.36). No statistical difference was found across BMI categories for either recurrent VTE (p-interaction≥0.43) or major bleeding (p-interaction ≥ 0.58) at any time point. In obese VTE patients, prescription of rivaroxaban was associated with a significantly reduced risk of recurrent VTE versus warfarin, without impacting major bleeding. Our findings remained consistent across BMI classes.

Rivaroxaban reversal with prothrombin complex concentrate or tranexamic acid in healthy volunteers

Essentials Specific reversal agents for managing severe factor Xa inhibitor-associated bleeding are lacking. We assessed 4-factor-prothrombin complex concentrate (4F-PCC) and tranexamic acid (TXA). 4F-PCC, but not TXA, reduced the prothrombin time and increased endogenous thrombin potential. These agents may be viable options for reversal of therapeutic doses of rivaroxaban.

SUMMARY

Background Oral activated factor X inhibitors such as rivaroxaban are widely used, but specific reversal agents are lacking. Although four-factor prothrombin complex concentrate (4F-PCC) and tranexamic acid (TXA) are sometimes used to manage serious bleeding, their efficacy is unknown. Prior studies in healthy subjects taking rivaroxaban revealed that 4F-PCC partially reverses the prolonged prothrombin time (PT), and fully restores the endogenous thrombin potential (ETP). The effect of TXA has not been evaluated. Methods In this double-blind, parallel-group study, 147 healthy volunteers given rivaroxaban 20 mg twice daily for 3 days were randomized after their morning dose on day 4 to receive intravenous 4F-PCC (50 IU kg-1 ), TXA (1.0 g), or saline. Standardized punch biopsies were performed at baseline and after 4F-PCC, TXA or saline administration. Reversal was assessed by measuring bleeding duration and bleeding volume at biopsy sites, and by determining the PT and ETP. Results As compared with saline, 4F-PCC partially reversed the PT and completely reversed the ETP, whereas TXA had no effect. Neither 4F-PCC nor TXA reduced bleeding duration or volume. All treatments were well tolerated, with no recorded adverse events. Conclusions Although 4F-PCC reduced the PT and increased the ETP in volunteers given supratherapeutic doses of rivaroxaban, neither 4F-PCC nor TXA influenced punch biopsy bleeding.

A Cross-Study Analysis Evaluating the Effects of Food on the Pharmacokinetics of Rivaroxaban in Clinical Studies

US prescribing guidelines recommend that 15- and 20-mg doses of rivaroxaban be administered with food for the treatment of deep vein thrombosis (DVT) and pulmonary embolism (PE) and for reduction in the risk of recurrence of DVT and PE. In addition, the US prescribing guidelines recommend these doses be administered with an evening meal to reduce the risk of stroke and systemic embolism in patients with nonvalvular atrial fibrillation (AF). The purpose of this model-based cross-study comparison was to examine the impact of food, with regard to both meal timing and content, on the pharmacokinetics (PK) of rivaroxaban, using data collected during its clinical development. Results of this analysis showed that a PK model built from pooled data in the AF population (for whom rivaroxaban was administered with an evening meal) and in the DVT population (for whom rivaroxaban was administered with a morning meal) can describe both data sets well. Furthermore, the PK model built from data in the AF population alone can adequately predict the PK profile of the DVT population and vice versa. This cross-study analysis also confirmed the findings from previous clinical pharmacology studies, which showed that meal content does not have a clinically relevant impact on the PK of rivaroxaban at 20 mg. Therefore, although the administration of rivaroxaban with food is necessary for maintaining high bioavailability, neither meal timing nor meal content appears to affect the PK of rivaroxaban.

Pharmacokinetics, Pharmacodynamics, and Safety of Single-Dose Rivaroxaban in Chronic Hemodialysis

BACKGROUND

This study aimed to characterize the single-dose pharmacokinetic (PK) and pharmacodynamic (PD) profile of rivaroxaban 15 mg administered before and after dialysis in subjects with end-stage renal disease (ESRD), and to compare this profile in subjects with ESRD to that in healthy control subjects (creatinine clearance ≥80 ml/min).

METHODS

This was an open-label, single-dose, single-center, parallel-group study of rivaroxaban in ESRD subjects who had been clinically stable on maintenance hemodialysis for ≥3 months. In 8 subjects with ESRD, a 15-mg dose of rivaroxaban was administered 2 ± 0.5 h before a hemodialysis session and repeated 7-14 days later at 3 h after a 4-h hemodialysis session. Eight healthy control subjects, matched for age, sex, and body mass index, received one 15-mg rivaroxaban dose.

RESULTS

Compared to healthy subjects, area under the rivaroxaban plasma concentration versus time curve (AUC) increased by 56% following post-dialysis administration. Assuming similar bioavailability between groups, this reflects an approximate 35% decrease in overall drug clearance in ESRD subjects. Pre-dialysis dosing resulted in only 5% lowering of AUC versus post-dialysis dosing, confirming the minimal impact of dialysis on the PK of rivaroxaban. PD effects, as assessed by change in prothrombin time, percent factor Xa inhibition, and anti-Xa activity, were generally concordant with observed changes in plasma PK.

CONCLUSIONS

Changes in PK and PD parameters in chronic dialysis patients were generally comparable to changes observed previously in patients with moderate-to-severe renal impairment who were not undergoing dialysis, and support use of a 15-mg dose in this patient population.

Switching from rivaroxaban to warfarin: an open label pharmacodynamic study in healthy subjects

Aims

The primary objective was to explore the pharmacodynamic changes during transition from rivaroxaban to warfarin in healthy subjects. Safety, tolerability and pharmacokinetics were assessed as secondary objectives.

Methods

An open label, non-randomized, sequential two period study. In treatment period 1 (TP1), subjects received rivaroxaban 20 mg once daily (5 days), followed by co-administration with a warfarin loading dose regimen of 5 or 10 mg (for the 10 mg regimen, the dose could be uptitrated to attain target international normalized ratio [INR] ≥2.0) once daily (2–4 days). When trough INR values ≥2.0 were attained, rivaroxaban was discontinued and warfarin treatment continued as monotherapy (INR 2.0–3.0). During treatment period 2, subjects received the same warfarin regimen as in TP1, but without rivaroxaban.

Results

During co-administration, maximum INR and prothrombin time (PT) values were higher than with rivaroxaban or warfarin monotherapy. The mean maximum effect (E_max) for INR after co-administration was 2.79–4.15 (mean PT E_max 41.0–62.7 s), compared with 1.41–1.74 (mean PT E_max 20.1–25.2 s) for warfarin alone. However, rivaroxaban had the smallest effect on INR at trough rivaroxaban concentrations. Neither rivaroxaban nor warfarin significantly affected maximum plasma concentrations of the other drug.

Conclusions

The combined pharmacodynamic effects during co-administration of rivaroxaban and warfarin were greater than additive, but the pharmacokinetics of both drugs were unaffected. Co-administration was well tolerated. When transitioning from rivaroxaban to warfarin, INR monitoring during co-administration should be performed at the trough rivaroxaban concentration to minimize the effect of rivaroxaban on INR.

Comparison of three-factor and four-factor prothrombin complex concentrates regarding reversal of the anticoagulant effects of rivaroxaban in healthy volunteers

BACKGROUND

Four-factor prothrombin complex concentrates (PCCs), which contain factor II, FVII, FIX, and FX, have shown the potential to reverse the anticoagulant effect of rivaroxaban in healthy volunteers. The purpose of this study was to determine whether a three-factor PCC, which contains little FVII, has a similar effect.

METHODS AND RESULTS

We performed an open-label, single-center, parallel-group study comparing the effect of a three-factor PCC (Profilnine SD) with that of a four-factor PCC (Beriplex P/N) on the pharmacodynamics of rivaroxaban in 35 healthy volunteers. After receiving 4 days of rivaroxaban 20 mg twice daily to obtain supratherapeutic steady-state concentrations, volunteers were randomized to receive a single 50 IU kg(-1) bolus dose of four-factor PCC, three-factor PCC or saline 4 h after the morning dose of rivaroxaban on day 5, and the effects of these interventions on prothrombin time and thrombin generation were determined. Within 30 min, four-factor PCC reduced mean prothrombin time by 2.5-3.5 s, whereas three-factor PCC produced only a 0.6-1.0-s reduction. In contrast, three-factor PCC reversed rivaroxaban-induced changes in thrombin generation more than four-factor PCC.

CONCLUSIONS

This study demonstrates the potential of both three-factor and four-factor PCCs to at least partially reverse the anticoagulant effects of rivaroxaban in healthy adults. The discrepant effects of the PCC preparations may reflect differences in the procoagulant components present in each.

Population pharmacokinetics and pharmacodynamics of rivaroxaban in patients with non-valvular atrial fibrillation: results from ROCKET AF

Two once-daily rivaroxaban dosing regimens were compared with warfarin for stroke prevention in patients with non-valvular atrial fibrillation in ROCKET AF: 20 mg for patients with normal/mildly impaired renal function and 15 mg for patients with moderate renal impairment. Rivaroxaban population pharmacokinetic (PK)/pharmacodynamic (PD) modeling data from ROCKET AF patients (n = 161) are reported and are used to confirm established rivaroxaban PK and PK/PD models and to re-estimate values of the models' parameters for the current AF population. An oral one-compartment model with first-order absorption adequately described rivaroxaban PK. Age, renal function, and lean body mass influenced the PK model. Prothrombin time and prothrombinase-induced clotting time exhibited a near-linear relationship with rivaroxaban plasma concentration; inhibitory effects were observed through to 24 hours post-dose. Rivaroxaban plasma concentration and factor Xa activity had an inhibitory maximum-effect (Emax ) relationship. Renal function (on prothrombin time; prothrombinase-induced clotting time) and age (on factor Xa activity) had moderate effects on PK/PD models. PK and PK/PD models were shown to be adequate for describing the current dataset. These findings confirm the modeling and empirical results that led to the selection of doses tested against warfarin in ROCKET AF.

X-ray emission spectroscopy of cerium across the γ-α volume collapse transition

High-pressure x-ray emission measurements are used to provide crucial evidence in the longstanding debate over the nature of the isostructural (α, γ) volume collapse in elemental cerium. Extended local atomic model calculations show that the satellite of the Lγ emission line offers direct access to the total angular momentum observable (J(2)). This satellite experiences a 30% steplike decrease across the volume collapse, validating the Kondo model in conjunction with previous measurements. Direct comparisons are made with previous predictions by dynamical mean field theory. A general experimental methodology is demonstrated for analogous work on a wide range of strongly correlated f-electron systems.

Solid debris collection for radiochemical diagnostics at the National Ignition Facility

Radiochemical analysis of post-ignition debris inside the National Ignition Facility (NIF) target chamber can help determine various diagnostic parameters associated with the implosion efficiency of the fusion capsule. This technique is limited by the ability to distinguish ablator material from other debris and by the collection efficiency of the capsule debris after implosion. Prior to designing an on-line collection system, the chemical nature and distribution of the debris inside the chamber must be determined. The focus of our current work has been on evaluating capture of activated Au hohlraum debris on passive foils (5 cm diameter, 50 cm from target center) post-shot. Preliminary data suggest that debris distribution is locally heterogeneous along the equatorial and polar line-of-sights.

Bioequivalence and safety of a novel fentanyl transdermal matrix system compared with a transdermal reservoir system

OBJECTIVES

Fentanyl is a potent synthetic opioid used for the management of chronic pain. A newer transdermal matrix system was developed and compared with a reservoir system used in the United States.

SETTING

An open-label, single-center, randomized, two-period crossover study was conducted to evaluate the bioequivalence of the transdermal matrix system to the transdermal reservoir system. Seventy-four subjects completed treatment with both the reservoir system (100 microg/h) and the matrix system (100 microg/h), each applied for 72 hours. After application of the first system, subjects completed a 9-day washout and then crossed over to receive the other system for another 72 hours.

MAIN OUTCOME MEASURE

Blood samples for the determination of serum fentanyl concentrations were taken in each treatment period for up to 120 hours following application.

RESULTS

The ratios of geometric means for maximum fentanyl concentration (Cmax) and area under the concentration-time curve (AUClast, and AUCinfinity) were 106 percent, 110 percent, and 110 percent, respectively. The 90% confidence intervals for the ratios of the geometric means were contained within the bioequivalence criteria of 80-125 percent. The matrix system adhered well to skin. Systemic and topical safety profiles were comparable between treatments.

CONCLUSIONS

The transdermal fentanyl matrix system adhered well, was well tolerated, and produced systemic exposures of fentanyl that were bioequivalent to the reservoir system.

Diffusionless γ⇄α phase transition in polycrystalline and single-crystal cerium

The cerium γ⇄α transition was investigated using high-pressure, high-temperature angle-dispersive x-ray diffraction measurements on both poly- and single-crystalline samples, explicitly addressing symmetry change and transformation paths. The isomorphic hypothesis of the transition is confirmed, with a transition line ending at a solid-solid critical point. The critical exponent is determined, showing a universal behavior that can be pictured as a liquid-gas transition. We further report an isomorphic transition between two single crystals (with more than 14% of volume difference), an unparalleled observation in solid-state matter interpreted in terms of dislocation-induced diffusionless first-order phase transformation.

Steady-state pharmacokinetics of extended-release hydromorphone (OROS hydromorphone): a randomized study in healthy volunteers

The steady-state pharmacokinetics of an extended-release formulation of hydromorphone, OROS hydromorphone, was investigated in a randomized, open-label, crossover study in healthy volunteers. Participants were randomly assigned to receive 16 mg of OROS hydromorphone once daily and 4 mg of immediate-release hydromorphone four times daily for five consecutive days. The two treatments were separated by a washout period of 7-14 days. Naltrexone was given throughout both treatment periods to block the opioid effects of hydromorphone. Steady-state hydromorphone concentrations were statistically analyzed using Helmert contrasts to determine when steady state was reached. A total of 30 participants were enrolled, of whom 29 completed both treatment periods. The two treatments produced comparable steady-state plasma drug concentrations, but peak-to-trough fluctuations were smaller with OROS hydromorphone (61 percent vs 172 percent) in comparison with immediate release hydromorphone. Overall systemic exposure to hydromorphone was similar between the two formulations. The ratio of the geometric means between the two formulations for the area under the concentration-time curves at steady state was 105.2 percent with a 90% confidence interval (CI) of 99.8-110.8 (geometric mean: 102.7 percent; 90% CI: 97.6-108.2 after correcting for measured drug content), which was within the bioequivalence range (80-125 percent). The analysis of Helmert contrasts showed that steady state conditions were attained by day 4. Both treatments were well tolerated. This study shows that OROS hydromorphone maintains steady-state plasma drug concentrations within the same range as immediate-release hydromorphone at the same total daily dose, with less fluctuation.

Emergence of strong exchange interaction in the actinide series: the driving force for magnetic stabilization of curium

Using electron energy-loss spectroscopy, many-electron atomic spectral calculations, and density functional theory, we show that angular-momentum coupling in the 5f states plays a decisive role in the formation of the magnetic moment in Cm metal. The 5f states of Cm in intermediate coupling are strongly shifted towards the LS coupling limit due to exchange interaction, unlike most actinide elements where the effective spin-orbit interaction prevails. Hund's rule coupling is the key to producing the large spin polarization that dictates the newly found crystal structure of Cm under pressure.

Symmetry and stability of plutonium: the influence of electronic structure

Using first-principles density-functional theory, we calculate the bond strengths between the 12 nearest neighbors in delta plutonium for both pure Pu and a Pu-3.7 at. % Ga alloy. Our results for pure Pu reveal a structure with the monoclinic space group Cm rather than face-centered cubic Fm3m, showing that the anomalously large anisotropy of delta plutonium is a consequence of greatly varying bond strengths between the 12 nearest neighbors. Further results for a Pu-3.7 at. % Ga alloy show that the nearest-neighbor bond strengths around a Ga atom are more uniform. Hence, our calculations address (i) why the ground state of Pu is monoclinic, (ii) why distortions of the delta phase are viable, with considerable implications for the behavior of the material as it ages due to anisotropic response to self-irradiation, and (iii) why Ga stabilizes face-centered cubic delta-Pu.

Probing the population of the spin-orbit split levels in the actinide 5f states

Spin-orbit interaction in the 5f states is believed to strongly influence exotic behaviors observed in actinide metals and compounds. Understanding these interactions and how they relate to the actinide series is of considerable importance. To address this issue, the branching ratio of the white-line peaks of the N4,5 edge for the light actinide metals, alpha-Th, alpha-U, and alpha-Pu were recorded using electron energy-loss spectroscopy (EELS) in a transmission electron microscope (TEM) and synchrotron-radiation-based X-ray absorption spectroscopy (XAS). Using the spin-orbit sum rule and the branching ratios from both experimental spectra and many-electron atomic spectral calculations, accurate values of the spin-orbit interaction, and thus the relative occupation of the j = 5/2 and 7/2 levels, are determined for the actinide 5f states. Results show that the spin-orbit sum rule works very well with both EELS and XAS spectra, needing little or no correction. This is important, since the high spatial resolution of a TEM can be used to overcome the problems of single-crystal growth often encountered with actinide metals, allowing acquisition of EELS spectra, and subsequent spin-orbit analysis, from nm-sized regions. The relative occupation numbers obtained by our method have been compared with recent theoretical results and they show a good agreement in their trend.

Applicability of the spin-orbit sum rule for the actinide 5f states

The branching ratio of core-valence transitions in electron energy-loss spectroscopy and x-ray absorption spectroscopy is linearly related to the expectation value of the spin-orbit operator of the valence states. Here, we analyze the branching ratio of the N(4,5) edges in the actinides and find that the spin-orbit sum rule gives an accurate result without the need to include the core-valence interactions. The branching ratio is not only useful to study the variations in the 5f spin-orbit interaction, it also allows us to constrain the 5f count for given angular-momentum coupling conditions.

Failure of Russell-Saunders coupling in the 5f states of plutonium

Using high energy-electron energy loss spectroscopy, transmission electron microscopy, and synchrotron-radiation-based x-ray absorption spectroscopy, we provide the first experimental evidence that Russell-Saunders (LS) coupling fails for the 5f states of Pu. These results support the assumption that only the use of jj or intermediate coupling is appropriate for the 5f states of Pu. High energy-electron energy loss spectroscopy experiments were performed by use of a transmission electron microscope and are coupled with image and diffraction data; therefore, the measurements are completely phase specific.

A tilting procedure to enhance compositional contrast and reduce residual diffraction contrast in energy-filtered TEM imaging of planar interfaces

This paper systematically demonstrates that energy-filtered transmission electron microscope (EFTEM) images of a planar interface between two single crystals have increased compositional contrast and decreased residual diffraction contrast when the sample is oriented so that the electron beam is parallel to the interface, but not directly on a zone axis. This off-axis orientation reduces diffraction contrast in the unfiltered (and zero-loss) image, which in turn, reduces residual diffraction contrast in single energy-filtered TEM (EFTEM) images, thickness maps, jump-ratio images, and elemental maps. Most importantly, this procedure produces EFTEM images that are more directly interpretable and, in most cases, possess superior spatial resolution compared to EFTEM images acquired directly on a zone axis.

Mechanistic studies of (porphinato)iron-catalyzed isobutane oxidation. Comparative studies of three classes of electron-deficient porphyrin catalysts

We report herein a comprehensive study of (porphinato)iron [PFe]-catalyzed isobutane oxidation in which molecular oxygen is utilized as the sole oxidant; these catalytic reactions were carried out and monitored in both autoclave reactors and sapphire NMR tubes. In situ 19F and 13C NMR experiments, coupled with GC analyses and optical spectra obtained from the autoclave reactions have enabled the identification of the predominant porphyrinic species present during PFe-catalyzed oxidation of isobutane. Electron-deficient PFe catalysts based on 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin [(C6F5)4PH2], 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(pentafluorophenyl) porphyrin [Br8(C6F5)4PH2], and 5,10,15,20-tetrakis(heptafluoropropyl) porphyrin [(C3F7)4PH2] macrocycles were examined. The nature and distribution of hydrocarbon oxidation products show that an autoxidation reaction pathway dominates the reaction kinetics, consistent with a radical chain process. For each catalytic system examined, PFeII species were shown not to be stable under moderate O2 pressure at 80 degrees C; in every case, the PFeII catalyst precursor was converted quantitatively to high-spin PFeIII complexes prior to the observation of any hydrocarbon oxidation products. Once catalytic isobutane oxidation is initiated, all reactions are marked by concomitant decomposition of the porphyrin-based catalyst. In situ 17O NMR spectroscopic studies confirm the incorporation of 17O from labeled water into the oxidation products, implicating the involvement of PFe-OH in the catalytic cycle. Importantly, Br8(C6F5)4PFe-based catalysts, which lack macrocycle C-H bonds, do not exhibit augmented stability with respect to analogous catalysts based on (C6F5)4PFe and (C3F7)4PFe species. The data presented are consistent with a hydrocarbon oxidation process in which PFe complexes play dual roles of radical chain initiator, and the species responsible for the catalytic decomposition of organic peroxides. This modified Haber-Weiss reaction scheme provides for the decomposition of tert-butyl hydroperoxide intermediates via reaction with PFe-OH complexes; the PFeIII species responsible for hydroperoxide decomposition are regenerated by reaction of PFeII with dioxygen under these experimental conditions.

A pilot study for a randomized controlled trial comparing the efficacy, safety and cost-effectiveness of surgical treatments of the prostate

OBJECTIVE

To assess the numbers of men in outpatients and subsequently undergoing transurethral resection of the prostate (TURP) who were referred during 1993-94 and 1996-97, thereby assessing the feasibility of a subsequent study of treatment efficacy in men with bladder outlet obstruction secondary to benign prostatic hyperplasia, prospectively randomized to the surgical treatment options, i.e. TURP, laser ablation of the prostate, transurethral needle ablation and T3 thermotherapy, to investigate treatment outcome, cost-efficacy and cost-benefit.

PATIENTS AND METHODS

All patients considered and consenting for prostate surgery were reviewed prospectively with a view to inclusion in the proposed trial. The diagnosis was based on two estimates of flow rate from voids of >150 mL and from symptoms assessed using the International Prostate Symptom Score. All patients had TURP explained by a urological surgeon and nursing staff, and subsequently had further consultation with research staff.

RESULTS

Patients seen in clinic as new referrals increased by 11% between the periods assessed, although the numbers undergoing TURP decreased by 19%. Of the 383 patients screened, who were on the waiting list for TURP, only 13 elected to enter the trial. Of the 383 men, 267 (67%) ultimately had prostate surgery, with 39 (10%) electing to continue with watchful waiting and 34 (9%) continuing with pharmacotherapy.

CONCLUSION

Although more men with benign prostatic disease and lower urinary tract symptoms are being seen in clinics, the reduced proportion of patients continuing to surgical intervention will lead to increasing difficulty in carrying out randomized controlled clinical trials assessing surgical options. With ever more therapeutic options available, patients find it difficult to make decisions in both the clinical situation and when asked to enter a trial. Fully informed decisions by both the surgeon and the patient will only be possible when objective data are available from trials that investigate outcome, cost-efficacy and cost-benefit. This study suggests that when presented with more information and counselling, fewer men decide to undergo prostate surgery for symptomatic BPH.

Understanding Interphase Boundary Dynamics by In Situ High-Resolution and Energy-Filtering Transmission Electron Microscopy and Real-Time Image Simulation

: This study discusses the use of in situ high-resolution transmission electron microscropy (HRTEM) techniques to determine the structure, composition, and interphase boundary dynamics during phase transformations at the atomic level. Three main in situ HRTEM techniques are described: (1) in situ HRTEM dynamic studies that are performed on the same precipitate plates from different viewing directions to determine the three-dimensional structure of the interfaces; (2) in situ compositional mapping of precipitate interfaces obtained by energy-filtering TEM experiments at temperature in a HRTEM, and (3) real-time HRTEM image simulations that are being created for comparison with and interpretation of experimental in situ HRTEM dynamic observations. The results from these studies demonstrate that it is possible to understand the mechanisms and kinetics of interphase boundary motion at the atomic level.

A prospective audit of the use of a prostate clinic

OBJECTIVE

To assess the efficiency of a prostate clinic and to determine the treatment outcomes and the proportion of patients who could potentially be managed by their General Practitioners (GPs).

PATIENTS AND METHODS

Referral letters from GPs were screened by the consultant urologists and appropriate patients seen in the next available prostate clinic. The initial assessment consisted of an International Prostate Symptom Score and a medical history, uroflowmetry, ultrasonographically determined post-void urine volumes, renal function tests and measurement of prostate specific antigen, in addition to a physical examination and a digital rectal examination. Further investigations were requested as required.

RESULTS

Over a period of 18 months, 403 patients were seen, 90% of them within 12 weeks from the time of referral. Uroflowmetry was performed in 96% of patients and further urodynamics in 22%. Bladder outlet obstruction was diagnosed in 246 (61%) patients and primary detrusor instability was detected in 20 (5%) patients. Fourteen per cent of patients were returned to the care of the GP following their first visit. The audit identified a potential group of patients (52%) who could be managed by their GP. Seven per cent underwent prostate surgery for the relief of bladder outlet obstruction.

CONCLUSION

The prostate clinic significantly reduced the delay for patients to be seen at the hospital and facilitated rapid assessment and investigation, much of which was carried out by a nurse practitioner during the first visit (in most cases). Several patients were identified who could be managed in the community.

Impotence in diabetes: aetiology, implications for treatment and preferred vacuum device

In an assessment of the contributions of autonomic neuropathy and vascular disease to the aetiology of male impotence in diabetes, evidence of autonomic neuropathy was identified in 23/39 (59%) individuals complaining of impotence. Thirteen of 26 men aged < 60 years tested with an intracorporeal injection of papaverine experienced little or no response and seven had tumescence but no rigidity. Radioisotope phallography demonstrated vascular disease in six of these seven, suggesting evidence of a vascular component in 19/26 (73%). Only one patient had non-organic impotence. Overall, evidence of vascular disease alone was demonstrated in 10/26 (38%), vascular disease plus autonomic neuropathy in 9/26 (35%), and autonomic neuropathy alone in 6/26 (23%). Many diabetic men complaining of impotence appear to have a significant vascular component which renders intracorporeal papaverine treatment ineffective. We compared the performance of a vacuum constriction-band (Erecaid) and condom-type (Synergist) device in 10 randomly selected men from this group. The devices, provided in random order for 5 months each, were assessed by questionnaire and interview of both the patient and partner. Two couples defaulted and another could use neither device. Although erectile capacity could be restored in the remainder, subsequent intercourse was only deemed satisfactory to both partners in five couples, who unanimously preferred the constriction-band device. In treatment with vacuum devices the constriction-band type seems to be the device of choice; the condom type should probably be reserved for those unable to use the constriction-band type.

Measurement of prostate-specific antigen and prostatic acid phosphatase concentrations in serum before and 1-42 days after transurethral resection of the prostate and orchidectomy

Preoperative intra-individual variation for determinations of prostate-specific antigen and prostatic acid phosphatase concentrations, 15-30% in 92 patients with benign prostatic hyperplasia, limits the diagnostic usefulness of both tumor markers. In benign prostatic hyperplasia (214 patients), concentrations of these tumor markers increased in the initial postoperative period. Prostatic acid phosphatase concentration then decreased by the third postoperative day. Prostate-specific antigen concentration remained above normal in the first postoperative week but had decreased by 42 days. In prostatic carcinoma (46 patients), the concentrations of these tumor markers did not increase postoperatively. During the first week, the concentrations of prostatic acid phosphatase began to fall, but prostate-specific antigen showed a decrease only at 42 days. After orchidectomy (11 patients), the concentrations of both markers had decreased by five days. Concentrations of prostate-specific antigen but not of prostatic acid phosphatase were significantly increased in patients with metastases at 42 days postoperatively. When the concentration of tumor marker did decrease, the magnitude of change was greater for prostatic acid phosphatase than for prostate-specific antigen. These changes were accentuated after an orchidectomy.

Systemic mannitol increases retinal adhesiveness measured in vitro

Pigmented rabbits were given mannitol intravenously, and at various times thereafter blood osmolality was measured and eyes were enucleated to measure retinal adhesiveness to the retinal pigment epithelium. Both blood osmolality and retinal adhesion increased in proportion to the dose of mannitol. We found a measurable increase in retinal adhesion as early as 10 minutes and as late as 4 hours after mannitol injection. We suspect that mannitol dehydrates the subretinal space and thereby enhances the adhesive properties of the interphotoreceptor matrix or tightens the interdigitation between photoreceptors and pigment epithelial cells. Our data suggest that mannitol could have clinical application in the management of retinal detachments.

The treatment of perforated duodenal ulcer

The prognosis of 189 patients with a perforated duodenal ulcer was analysed. There were three treatment groups, non-operative, simple closure and definitive ulcer surgery. The prognosis of the patients was analysed in terms of the chronicity of the ulcer. Perforations occurring in acute duodenal ulcers have an excellent prognosis, with similar results in each group in this series. All perforations of chronic duodenal ulcers should be treated by emergency surgery.

Canine small bowel transplantation. A study of the immunological responses

A canine small bowel allograft model was used to determine the effects of radiation to the graft in modifying the immunological effects of the passenger leukocytes. When untreated allografts were transplanted, death of the recipient animals occurred at a mean of nine days. The allograft was well-preserved and showed no signs of rejection. The reasons for attributing death to graft-versus-host (GVH) disease are discussed. When allografts were treated with 150 rads prior to transplantation, allograft rejection occurred, with death of the recipient animals at a mean of 9.2 days. This was the only group in which cell-mediated immunity developed. When allografts were treated with 50 rads, prolonged survival of the recipients to a mean of 28 days was noted. It is postulated that in this group a balance was struck between the allograft rejection reaction and GVH disease, with prolongation of allograft survival.