Hemorrhagic and thrombotic events associated with generic substitution of warfarin in patients with atrial fibrillation: a retrospective analysis

Structural Changes of Sodium Warfarin in Tablets Affecting the Dissolution Profiles and Potential Safety of Generic Substitution

At present, the risk of generic substitutions in warfarin tablets is still being discussed. The aim of this study was to assess whether API interactions with commonly used excipients may affect the safety of generic replacement of warfarin sodium tablets. These interactions were observed during an accelerated stability study, and the effect of the warfarin solid phase (crystalline/amorphous form) as well as the API particle size distribution was studied. Commercial tablets and prepared tablets containing crystalline warfarin or amorphous warfarin were used. In addition, binary mixtures of warfarin with various excipients were prepared. The structural changes before and after the stability study were monitored by dissolution test in different media, solid-state NMR spectroscopy and Raman microscopy. During the stability study, the conversion of the sodium in warfarin to its acid form was demonstrated by some excipients (e.g., calcium phosphate). This change in the solid phase of warfarin leads to significant changes in dissolution, especially with the different particle sizes of the APIs in the tablet. Thus, the choice of suitable excipients and particle sizes are critical factors influencing the safety of generic warfarin sodium tablets.

Differences in brand versus generic esmolol in the treatment of perioperative supraventricular tachycardia and hypertension: A pilot study

Background:

Once a patent expires, generic analogue drugs are alternatives to brand name drugs. Because bioequivalence/biodistribution problems have been reported for many generic analogue drugs, we prospectively evaluated 31 patients to reveal the differences in the doses used and the efficacy and adverse events of two different intravenous esmolol formulations.

Methods:

This was a prospective observational pilot study. Our aim was to reveal the possible differences in the required doses between two different formulations (brand name drug vs generic analogue drug) of intravenous esmolol in beats per minute, systolic blood pressure, diastolic blood pressure and mean arterial pressure in intra- and postoperative patients with supraventricular tachycardia and hypertension. The patients were categorised into two groups according to the medication they received (brand name drug or generic analogue drug).

Results:

Esmolol was given to 31 patients (16 generic analogue drug and 15 brand name drug). Although there was a statistically significant difference in bolus (mg/kg) and continued (mg/kg/h) drug dose used (brand name drug/generic analogue drug, mean (standard deviation), 0.3 (0.1) vs 0.38 (0.1), p = 0.03 for bolus dose, and 0.22 (0.09) vs 0.29 (0.08) for continued dose at 10 min (p = 0.03), 0.19 (0.06) vs 0.24 (0.05) at 20 min (p = 0.01) and 0.14 (0.05) vs 0.18 (0.05) at 30 min (p = 0.02)), there were no time-related statistical significant differences in the reduction rates of the two drugs (p = 0.47). There were no time-related statistically significant differences between the two groups in systolic blood pressure, diastolic blood pressure, mean arterial pressure and beats per minute, nor in their adverse events.

Conclusion:

In this pilot study, smaller doses were given for controlling the patient’s haemodynamics when a brand name drug was used. Because there were no significant time-related differences in the reduction rates of the two drugs nor in any haemodynamic differences between the two groups, optimal titration of the drug used could effectively control the patient’s haemodynamics. The adverse events were also similar in both groups.

Public Health Outcomes May Differ After Switching from Brand-Name to Generic Angiotensin II Receptor Blockers

Background

It is unclear whether generics are as safe as brand-name drugs in cardiology. For public health surveillance purposes, we evaluated if switching from the brand-name losartan, valsartan, or candesartan impacted the occurrence of the following outcomes: emergency room (ER) consultations, hospitalizations, or death.

Study Design

This was a retrospective cohort study.

Methods

This study was conducted in the Quebec Integrated Chronic Disease Surveillance System, including healthcare administrative data of the population of Quebec, Canada. We included brand-name users of losartan, valsartan, or candesartan aged ≥ 66 years who had undergone ≥ 30 days of stable treatment on the brand-name drug prior to cohort entry (substitution time-distribution matching was used to prevent immortal time bias). Outcomes up to 1 year were compared between groups using multivariable Cox proportional hazards regression models (validity assumptions were verified).

Results

In our cohorts (losartan, n =15,783; valsartan, n =16,907; candesartan, n =26,178), mean age was 76–78 years, 59–66% were female, 90–92% had hypertension, and 13–15% had heart failure. Validity assumptions were violated for losartan only. For patients switched to generic valsartan, the hazard ratio (95% confidence interval) was 1.07 (0.99–1.14) for ER consultation, 1.26 (1.14–1.39) for hospitalization, and 1.01 (0.61–1.67) for death. The corresponding rates for candesartan were 1.00 (0.95–1.05), 0.96 (0.89–1.03), and 0.57 (0.37–0.88), respectively.

Conclusions

We observed an increased risk of hospitalizations for patients switched to generic valsartan, and a decreased risk of death for patients switched to generic candesartan, compared with those who continued taking the brand-name drug. The differences between generic and brand-name drugs may lead to some differences in public health outcomes, but this safety signal must be further studied using other cohorts and settings.

Electronic supplementary material

The online version of this article (10.1007/s40268-020-00307-2) contains supplementary material, which is available to authorized users.

Are Generic Drugs Used in Cardiology as Effective and Safe as their Brand-name Counterparts? A Systematic Review and Meta-analysis

BACKGROUND

Previous systematic reviews (2008; 2016) concluded similarity in outcomes between brand-name and generic drugs in cardiology, but they included ≥ 50% comparative bioavailability studies, not designed or powered to detect a difference in efficacy or safety between drug types. We aimed to summarise best-evidence regarding the effectiveness and safety of generic versus brand-name drugs used in cardiology.

METHODS

For this systematic review of the literature, scientific databases (MEDLINE and EMBASE) were searched from January 1984 to October 2018. Original research reports comparing the clinical impact of brand-name versus generic cardiovascular drugs on humans treated in a real-life setting, were selected. Meta-analyses and subgroup analyses were performed. Heterogeneity (I²) and risk of bias were tested.

RESULTS

Among the 3148 screened abstracts, 72 met the inclusion criteria (n ≥ 1,000,000 patients, mean age 65 ± 10 years; 42% women). A total of 60% of studies showed no difference between drug types, while 26% concluded that the brand-name drug was more effective or safe, 13% were inconclusive and only 1% concluded that generics did better. The overall crude risk ratio of all-cause hospital visits for generic versus brand-name drug was 1.14 (95% confidence interval: 1.06-1.23; I²: 98%), while it was 1.05 (0.98-1.14; I²: 68%) for cardiovascular hospital visits. The crude risk ratio was not statistically significant for randomised controlled trials only (n = 4; 0.92 [0.63-1.34], I²: 35%).

CONCLUSION

The crude risk of hospital visits was higher for patients exposed to generic compared to brand-name cardiovascular drugs. However, the evidence is insufficient and too heterogeneous to draw any firm conclusion regarding the effectiveness and safety of generic drugs in cardiology.

Predicting Cost-Effectiveness of Generic vs. Brand Dabigatran Using Pharmacometric Estimates Among Patients with Atrial Fibrillation in the United States

Generic entry of newer anticoagulants is expected to decrease the costs of atrial fibrillation management. However, when making switches between brand and generic medications, bioequivalence concerns are possible. The objectives of this study were to predict and compare the lifetime cost‐effectiveness of brand dabigatran with hypothetical future generics. Markov microsimulations were modified to predict the lifetime costs and quality‐adjusted life years of patients on either brand or generic dabigatran from a US private payer perspective. Event rates for generics were predicted using previously developed pharmacokinetic‐pharmacodynamic models. The analyses showed that generic dabigatran with lower‐than‐brand systemic exposure were dominant. Meanwhile, generic dabigatran with extremely high systemic exposure was not cost‐effective compared with the brand reference. Cost‐effectiveness of generic medications cannot always be assumed as shown in this example. Combined use of pharmacometric and pharmacoeconomic models can assist in decision making between brand and generic pharmacotherapies.

Trends in Hospital Visits for Generic and Brand-Name Warfarin Users in Québec, Canada: A Population-Based Time Series Analysis

BACKGROUND

Federal standards authorize the commercialization of generic medicines after bioequivalence versus the brand-name originator has been demonstrated. For drugs with narrow therapeutic indexes, such as warfarin, the accepted difference in bioavailability is ≤ 10%. No systematic pharmacovigilance studies are conducted once generics become available.

OBJECTIVE

We aimed to assess the impact of the arrival of generic warfarin on hospital visit trends (hospital admissions or emergency room consultations) in warfarin users.

METHODS

This was an observational interrupted time series analysis (2 January 1996 to 1 January 2016). Using the Québec Integrated Chronic Disease Surveillance System, we included all patients who were aged ≥ 66 years, publicly covered and using brand-name or generic warfarin (N = 280,158). We estimated rates of hospital visits in 6-month periods, 5 years before and up to 15 years after the arrival of generic warfarin. Periods before and after were compared using segmented regression models for all users along with exploratory (generic vs. brand name)/subgroup analyses (cardiovascular comorbidities and socioeconomic status).

RESULTS

Generic warfarin arrived on the market on 2 January 2001. Over the 20-year period of the study, the mean rate of hospital visits was 113 for 100 brand-name or generic users per 6-month period and was similar before and after the arrival of the generics. Up to 15 years after the arrival of the generics, the rates of hospital visits were 10% higher for generic than for brand-name users, which was confirmed by subgroup analyses.

CONCLUSIONS

Overall, we observed no impact on hospital visits after the arrival of generic warfarin in all the population treated with any type of warfarin. However, a higher crude rate of hospital visits among generic users than brand-name users remains to be validated using a different methodology and specific outcomes.

Therapy discontinuation or substitution in patients with cardiovascular disease, switching among different products of the same off-patent active substance: a 'real-world' retrospective cohort study

OBJECTIVE

The present study investigated the effects of switching to different products of the same off-patent active substance (brand name or generic) on therapy discontinuation or substitution with another molecule of the same class, in patients with cardiovascular disease treated with statins and antihypertensives in a 'real-world' setting.

DESIGN

A retrospective cohort study in a 'real-world' setting.

SETTING

Analysis of data performed by integrating administrative databases that included approximately two million individuals who are assisted by the National Health System from three Local Health Units located in three different regions of Italy.

PARTICIPANTS

All patients aged ≥18 years with at least one prescription of simvastatin, ramipril or amlodipine in the period 1 January to 31 December 2010 were included and followed up for 2 years.

MAIN OUTCOME MEASURES

Prescription refills occurring during follow-up were evaluated. Frequency of discontinuation of therapy or substitution with another molecule of the same class (eg, from simvastatin to a different statin) during follow-up was identified.

RESULTS

During follow-up, therapy discontinuation or substitution was found to be more frequent in patients switching to a different product of the same active substance compared with non-switching patients (11.5% vs 10.8% and 22.2% vs 20.8% (p=0.002), respectively, in the simvastatin group; 4.0% vs 3.5% and 24.6% vs 22.7% (p<0.001), respectively, in the amlodipine group). In the ramipril group, 8% of patients undertook a therapy substitution to another molecule; no trend towards a lower percentage of substitution was observed in the non-switching group, while 18% of patients discontinued treatment, with a significant difference in favour of patients not switching. These findings were partially confirmed by multivariate analysis.

CONCLUSIONS

Switches among products of the same active substance are quite common in patients with cardiovascular disease. Our study suggests that switching may expose patients to a higher risk of therapy discontinuation or substitution.

Evaluation of pharmaceutical concerns in Germany: frequency and potential reasons

Background:

Generic substitution can have unintended consequences. In Germany, brand name to generic or generic to generic switching is mainly driven by rebate contracts. Frequent switching may raise concerns about bio- and therapeutic equivalence. Expected patient confusion may result in compromised medication adherence or new onset of other drug-related problems. Since 2008, pharmacists are allowed to deviate from rebate contracts by denying substitution due to pharmaceutical concerns on an individual basis.

Objectives:

To explore the frequency of documented pharmaceutical concerns in Germany between July 2011 and December 2013 and to identify the medicines most frequently related to pharmaceutical concerns in 2013.

Methods:

We analyzed documented pharmaceutical concerns in all prescribed drugs at the expense of any statutory health insurance company requiring pharmacies’ generic substitution according to rebate contracts.

Results:

Since July 2011, the frequency of documented pharmaceutical concerns in relation to prescribed drug products with rebate contracts requiring substitution increased consistently and doubled between July 2011 and July 2013. Overall in 2013, the trend of the two previous years continued and reached approximately 1.5%. The most affected drugs/drug classes were thyroid hormones (in particular combinations with iodide; 15.9%) followed by ondansetron (12.5%), and levothyroxine (11.3%). For all drugs/drug classes under investigation, product-, patient- or disease-related aspects could be identified which are potential reasons to deny substitution and to document pharmaceutical concerns.

Conclusions:

Although there is no electronic recording of the specific reasons for pharmaceutical concerns in claims data, our analyses support the assumption that pharmacists make use of this instrument based on individual clinical decisions and as required by contract. Pharmaceutical concerns are, therefore, an important instrument for pharmacies to refuse generic substitution. They are considered to prevent compromised medication safety and to assure pharmacotherapy effectiveness in a generic substitution environment driven by low drug prizes above all.

The Impact of Generic Substitution on Health and Economic Outcomes: A Systematic Review

BACKGROUND

Generic drugs are considered therapeutically equivalent to their original counterparts and lower in acquisition costs. However, the overall impact of generic substitution (GS) on global clinical and economic outcomes has not been conclusively evaluated.

OBJECTIVE

To test whether (1) generics and original products yield the same health outcomes, and (2) generic therapies save economic resources versus original therapies.

METHODS

We performed a systematic literature review in Medline, Embase, and the Cochrane Database of Systematic Reviews to identify original studies that examine clinical or economic outcomes of GS. After standardized data extraction, reported outcomes were categorized as supporting or rejecting the hypotheses. Each reported outcome was assessed and accounted for supporting and opposing GS. One publication could provide multiple outcome comparisons.

RESULTS

We included 40 studies across ten therapeutic areas. Fourteen studies examined patients on de novo therapy; 24 studies investigated maintenance drug therapy, and two studies considered both settings. Overall, 119 outcome comparisons were examined. Of 97 clinical outcome comparisons, 67% reported no significant difference between generic drugs and their off-patent counterparts. Of 22 economic comparisons, 64% suggested that GS increased costs. Consequently, hypothesis (1) was supported but hypothesis (2) was not. We found no major differences among studies that investigated clinical outcomes with de novo or maintenance therapy.

CONCLUSION

The review suggests that clinical effects are similar after GS. However, economic savings are not guaranteed. More systematic research comparing clinical and economic outcomes with or without GS is needed to inform policy on the use of generic substitution.

Need for multicriteria evaluation of generic drug policies

Policymakers tend to focus on improving patented drug policies because they are under pressure from patients, physicians, and manufacturers to increase access to novel therapies. The success of pharmaceutical innovation over the last few decades has led to the availability of many off-patent drugs to treat disease areas with the greatest public health need. Therefore, the success of public health programs in improving the health status of the total population is highly dependent on the efficiency of generic drug policies. The objective of this article was to explore factors influencing the true efficiency of generic prescription drug policies in supporting public health initiatives in the developed world. Health care decision makers often assess the efficiency of generic drug policies by the level of price erosion and market share of generics. Drug quality, bioequivalence, in some cases drug formulations, supply reliability, medical adherence and persistence, health outcomes, and nondrug costs, however, are also attributes of success for generic drug policies. Further methodological research is needed to measure and improve the efficiency of generic drug policies. This also requires extension of the evidence base of the impact of generic drugs, partly based on real-world evidence. Multicriteria decision analysis may assist policymakers and researchers to evaluate the true value of generic drugs.

Stroke and Bleeding Risks in Patients with Atrial Fibrillation

Atrial fibrillation (AF) is the most common cardiac arrhythmia and is associated with a substantial risk of stroke and mortality. Strokes in patients with AF are associated with a greater disability and poorer outcomes than strokes in patients in sinus rhythm. Patients with AF are at increased risk of bleeding, especially if they use anticoagulant therapy. Recent research in the field of anticoagulation has led to development of new anticoagulants for stroke prevention in addition to antiplatelet agents and warfarin. This review discusses the role of AF as a risk factor for stroke and evaluates the role of various schemes for predicting the risk of stroke and bleeding in patients with AF.

Self-nanoemulsifying drug delivery system of lutein: physicochemical properties and effect on bioavailability of warfarin

Objective of present study was to prepare and characterize self-nanoemulsifying drug delivery system (SNEDDS) of lutein and to evaluate its effect on bioavailability of warfarin. The SNEDDS was prepared using an oil, a surfactant, and co-surfactants with optimal composition based on pseudo-ternary phase diagram. Effect of the SNEDDS on the bioavailability of warfarin was performed using Sprague Dawley rats. Lutein was successfully formulated as SNEDDS for immediate self-emulsification and dissolution by using combination of Peceol as oil, Labrasol as surfactant, and Transcutol-HP or Lutrol-E400 as co-surfactant. Almost complete dissolution was achieved after 15 min while lutein was not detectable from the lutein powder or intra-capsule content of a commercial formulation. SNEDDS formulation of lutein affected bioavailability of warfarin, showing about 10% increase in C_max and AUC of the drug in rats while lutein as non-SNEDDS did not alter these parameters. Although exact mechanism is not yet elucidated, it appears that surfactant and co-surfactant used for SNEDDS formulation caused disturbance in the anatomy of small intestinal microvilli, leading to permeability change of the mucosal membrane. Based on this finding, it is suggested that drugs with narrow therapeutic range such as warfarin be administered with caution to avoid undesirable drug interaction due to large amount of surfactants contained in SNEDDS.

Major bleeding in patients with atrial fibrillation receiving vitamin K antagonists: a systematic review of randomized and observational studies

AIMS

Clinical trials have shown that anticoagulation with vitamin K antagonists (VKAs), e.g. warfarin, decreases the risk of stroke in patients with atrial fibrillation (AF); however, increased bleeding risk is one of the safety concerns. The primary objective was to conduct a systematic review of the published literature, assessing the risk of major bleeding and mortality in patients with AF treated with VKAs.

METHODS AND RESULTS

Online searches of MEDLINE, EMBASE, BIOSIS, and the Cochrane Library were performed to a pre-specified protocol from 1960 to March 2012 for randomized controlled trials (RCTs) and from January 1990 to March 2012 for observational studies. A total of 47 studies (16 RCTs and 31 observational studies) were included. Cumulative follow-up was 61,563 patient-years for RCTs and 484 241 patient-years for observational studies. The overall median incidence of major bleeding was 2.1 per 100 patient-years (range, 0.9-3.4 per 100 patient-years) for RCTs and 2.0 per 100 patient-years (range, 0.2-7.6 per 100 patient-years) for observational studies. With study year as a proxy for changing management patterns, some evidence of bleeding rates and/or their reporting increasing over time was noted. Mortality rates from observational studies were inadequately reported to allow comparison with those from RCT data.

CONCLUSION

The median rate of major bleeding in observational studies and RCTs is similar. The larger heterogeneity in bleeding rates observed in a real-life setting could reflect a high variability in standard of care of patients on VKAs and/or methodological differences between observational studies and/or variability in data sources.

Resource Use and Cost Implications of Switching Among Warfarin Formulations in Atrial Fibrillation Patients

Background:

Despite the uncertainty surrounding the safety of switching warfarin formulations, limited data exist on the resource use and costs associated with this switching pattern.

Objective:

To evaluate health care resource use and costs associated with switching warfarin formulations among patients with atrial fibrillation (AF) in a managed care organization.

Methods:

Patients diagnosed with AF (ICD-9 427.31) between July 2004 and August 2008 and who received warfarin therapy were identified in the HealthCore Integrated Research Database and categorized into 3 groups: users of generic warfarin formulations from a single drug manufacturer (generic-only group), users of branded warfarin formulations only (brand-only group), and patients who used generic and branded warfarin therapy interchangeably or who may have used generic drugs from 1 or more manufacturers (generic/brand switching group). Patients were followed 12 months or longer after their index warfarin prescription date to compare all-cause resource use and costs using multivariable regression analysis.

Results:

The analysis included 12,908 patients: 71.82% were in the generic-only group, 9.61% were in the brand-only group, and 18.57% were in the generic/brand switching group. Patients in the generic/brand switching group were more likely to be hospitalized (relative risk [RR] = 1.43, p < 0.0001) or to use emergency department services (RR = 1.20, p < 0.01), compared to the brand-only users. Hospitalizations were more likely (RR = 1.26, p < 0.001) to occur among generic-only users versus brand-only users. Adjusted mean pharmacy costs per member per month were lower in the generic/brand switching group compared to the brand-only group ($257 vs $273, p = 0.038), but inpatient costs were higher ($1250 vs $972, p < 0.001), resulting in higher ($2125 vs $1847, p < 0.001) total costs. Generic-only users had lower pharmacy costs compared to brand-only users ($246 vs $273, p < 0.001), but total health care costs trended to be higher in the generic-only group ($1957 vs $1847, p = 0.053).

Conclusions:

The use of both generic and branded formulations of warfarin interchangeably, or the use of generics from more than 1 manufacturer, was associated with increased use of all-cause health care resources and total costs in patients with AF.

Deficiencies of the FDA in evaluating generic formulations: addressing narrow therapeutic index drugs

Generic drugs represent a significant portion of the medical arsenal in treating disease. As copies of originator drugs, these drugs have been permitted abbreviated approval under the Hatch-Waxman Act. Yet with the current cost focus upon generic formulations, potential safety issues with generics have arisen. Although there is an established criterion of "bioequivalence" that generic formulations must demonstrate, narrow-therapeutic index drugs for sensitive clinical circumstances such as epilepsy, antiplatelet therapies, and mental health treatments may require different regulatory treatment than other generic drugs. Further, in these circumstances, differences in generic formulations may lead to adverse clinical outcomes due to less stringent bioequivalence tolerances. Yet there is no mandate for comparison between different generic formulations. Countries outside the United States advocate for narrowing tolerance ranges for these high risk health situations and the drugs for their treatment. We argue in this paper that additional patient safety matters must be taken into account for narrow therapeutic disease drugs, and regulatory bodies should emphasize greater tightness in bioequivalence before these narrow-therapeutic drug generic formulations are approved.

Substituting Warfarin Products: What's the Source of the Problem?

Many clinicians have expressed concerns about the bioequivalence of warfarin products, and data suggest that substituting warfarin products may increase the risk of major bleeding and thromboembolic complications. Anecdotal reports and some retrospective studies have reported differences in anticoagulation control after a warfarin product substitution. But the best available evidence—prospective, randomized, blinded clinical trials—has failed to validate these observations. Indeed, interpatient and intrapatient variability in anticoagulation control observed before and after warfarin product substitution is very similar. So, while differences in product standardization, bioavailability, and bioequivalence make a convenient explanation, the problem lies elsewhere. Perhaps poor communication, fractionated systems of care, and errors are the culprits.