Generic warfarin: a cost-effective alternative to brand-name drug or a clinical wild card?

Clinical equivalence of generic and brand-name drugs used in cardiovascular disease: a systematic review and meta-analysis

CONTEXT

Use of generic drugs, which are bioequivalent to brand-name drugs, can help contain prescription drug spending. However, there is concern among patients and physicians that brand-name drugs may be clinically superior to generic drugs.

OBJECTIVES

To summarize clinical evidence comparing generic and brand-name drugs used in cardiovascular disease and to assess the perspectives of editorialists on this issue.

DATA SOURCES

Systematic searches of peer-reviewed publications in MEDLINE, EMBASE, and International Pharmaceutical Abstracts from January 1984 to August 2008.

STUDY SELECTION

Studies compared generic and brand-name cardiovascular drugs using clinical efficacy and safety end points. We separately identified editorials addressing generic substitution.

DATA EXTRACTION

We extracted variables related to the study design, setting, participants, clinical end points, and funding. Methodological quality of the trials was assessed by Jadad and Newcastle-Ottawa scores, and a meta-analysis was performed to determine an aggregate effect size. For editorials, we categorized authors' positions on generic substitution as negative, positive, or neutral.

RESULTS

We identified 47 articles covering 9 subclasses of cardiovascular medications, of which 38 (81%) were randomized controlled trials (RCTs). Clinical equivalence was noted in 7 of 7 RCTs (100%) of beta-blockers, 10 of 11 RCTs (91%) of diuretics, 5 of 7 RCTs (71%) of calcium channel blockers, 3 of 3 RCTs (100%) of antiplatelet agents, 2 of 2 RCTs (100%) of statins, 1 of 1 RCT (100%) of angiotensin-converting enzyme inhibitors, and 1 of 1 RCT (100%) of alpha-blockers. Among narrow therapeutic index drugs, clinical equivalence was reported in 1 of 1 RCT (100%) of class 1 antiarrhythmic agents and 5 of 5 RCTs (100%) of warfarin. Aggregate effect size (n = 837) was -0.03 (95% confidence interval, -0.15 to 0.08), indicating no evidence of superiority of brand-name to generic drugs. Among 43 editorials, 23 (53%) expressed a negative view of generic drug substitution.

CONCLUSIONS

Whereas evidence does not support the notion that brand-name drugs used in cardiovascular disease are superior to generic drugs, a substantial number of editorials counsel against the interchangeability of generic drugs.

Warfarin in the secondary prevention of thromboembolism in atrial fibrillation: impact of bioavailability on costs and outcomes

BACKGROUND

The bioavailability of warfarin is an important factor affecting the achievement of therapeutic anticoagulation. It is uncertain whether less expensive generic preparations of warfarin would compromise prevention of thromboembolism or increase bleeding risk in patients with atrial fibrillation.

OBJECTIVE

To compare the cost effectiveness of strategies using warfarin products with variable bioavailability in patients with a prior stroke or transient ischaemic attack related to atrial fibrillation.

DESIGN

A Markov decision-analytic model simulating health and economic outcomes over 1 year using the perspective of a government provincial payer was created. Four strategies were compared (where F = 1 is the assumed bioavailability of the branded/reference product): (i) warfarin F = 1; (ii) warfarin F = 1.25; (iii) warfarin F = 0.80; and (iv) alternating warfarin F = 1.25 and 0.80 every other month. Direct medical costs for drugs, physician fees, laboratory testing and hospitalisation for morbid events were obtained from a government payer, a local accounting system and the medical literature. The cost of warfarin F = 1 was equivalent to the cost of the brand name warfarin and the cost of warfarin F not equal 1 was equivalent to generic warfarin.

RESULTS

In our institution, warfarin F = 1 was similar in cost to the other three strategies (Can dollars 1361 vs Can dollars 1334-1613) and may be more effective than switching between generic preparations which have bioavailabilities at the extremes of acceptable limits (thromboembolism and bleeds 7. 1% vs 9.3%).

CONCLUSIONS

In patients with atrial fibrillation and a prior ischaemic stroke or transient ischaemic attack, the use of one warfarin agent within the range of acceptable bioavailability can be considered economically attractive from the healthcare perspective.

Economic consequences of underuse of generic drugs: evidence from Medicaid and implications for prescription drug benefit plans

OBJECTIVE

To calculate the financial impact of underuse of generic medications in state Medicaid programs.

DATA SOURCES/STUDY SETTING

State-by-state data on Medicaid drug spending for 48 states and the District of Columbia in calendar year 2000.

STUDY DESIGN

We compared the total amount paid by each state Medicaid program for brand name prescriptions with the amount that would have been paid for generic versions of the same agent, to estimate the level of unrealized savings from use of substitutable generic drugs. We also examined whether variation in prices between states represented a potential source of unrealized savings.

PRINCIPAL FINDINGS

Analysis of state-by-state Medicaid prescription drug spending in 2000 identified potential savings of $229 million that could have been realized from greater use of generic drugs. If the best available prices from each state had been used nationally, savings would have increased to $450 million. The majority of the unrealized savings were concentrated in a small group of medications, including clozapine, alprazolam, and levothyroxine.

CONCLUSIONS

Federal regulations on prescription drug reimbursement limit the excess spending on brand name drugs in the Medicaid program to a small percentage of total spending, although the absolute dollar amount is large. Further savings could be realized if lowest available prices were used nationwide. Concentrating on specific agents may be a productive way to address the unrealized savings.

Evaluation of the clinical and economic impact of a brand name-to-generic warfarin sodium conversion program

BACKGROUND

Substitution of generic warfarin initially was discouraged because of concerns regarding therapeutic failure or toxicity. Although subsequent research with AB-rated (i.e., bioequivalent) warfarin did not confirm initial concerns, the issue is not settled for all clinicians.

OBJECTIVES

We sought to provide additional information regarding the clinical and economic impact of warfarin conversion by analyzing a real-life sample of patients receiving long-term anticoagulation therapy who were switched from brand name to generic warfarin.

METHODS

Patients who had been taking warfarin for at least 180 days and had received uninterrupted oral anticoagulation 90 days before and 90 days after switching to generic warfarin were included. The switch date was based on the first time generic warfarin was dispensed from our pharmacies. The primary end point was the calculated amount of time each patient's international normalized ratio (INR) values were within the patient-specific target INR range in the 90 days before and after the switch. Data regarding adverse events and medical resource utilization were also collected. Pharmacoeconomic analyses were performed.

RESULTS

The analysis included 2299 patients. The overall difference in calculated time INR values were below (22.6% before vs 26.1% after switch, p<0.0001) and within (65.9% before vs 63.3% after switch, p=0.0002) the therapeutic INR range was statistically but not clinically significant. Only 28.0% of patients experienced a change in therapeutic INR control of 10% or less, 33.1% experienced INR control that improved by greater than 10%, and 38.9% experienced INR control that worsened by more than 10%. The difference in total treatment costs associated with brand name and generic warfarin was 3128 dollars/100 patient-years in favor of the generic product. Sensitivity analyses revealed that cost savings associated with warfarin conversion in this health care system were highly dependent on the difference between warfarin costs and cost of treating anticoagulation-related adverse events.

CONCLUSIONS

Most of these patients were successfully switched from brand name to generic warfarin. However, supplemental INR monitoring is warranted when one warfarin product is substituted for another to allow timely detection of those patients who experience significant changes in anticoagulation response.

Substitution of generic warfarin for Coumadin in an HMO setting

BACKGROUND

Substitution of generic warfarin for Coumadin presents safety concerns due to warfarin's narrow therapeutic index and because a prior generic formulation was removed from the US market after it was associated with adverse events.

OBJECTIVE

To determine whether a health maintenance organization (HMO) can add generic warfarin to its formulary without adversely affecting warfarin management or increasing adverse events.

DESIGN

In a prospective, observational study, an HMO that formerly dispensed only Coumadin added a generic warfarin preparation (Barr Laboratories, Pomona, NY) to its formulary.

SETTING

An anticoagulation service (ACS) affiliated with an HMO that was based in St. Louis, MO.

PARTICIPANTS

The cohort consisted of 182 enrollees in the ACS as of May 1, 1999. At the start of the study, these participants were taking Coumadin; by October 31, 2000, all had switched to Barr warfarin.

MEASUREMENTS AND MAIN RESULTS

We collected data 8 months prior to and 10 months after the introduction of generic warfarin for the following endpoints: international normalized ratio (INR) control, frequency of INR monitoring, number of dose changes, and rate of thrombotic and hemorrhagic events. Statistical process control charts were used to differentiate between random variation in the endpoints and changes due to different warfarin formulations, and we used the Wilcoxon signed-rank test to look for a change in any endpoint after patients changed to generic warfarin. No significant differences were found in any endpoint.

CONCLUSIONS

Substitution of Barr warfarin for Coumadin did not significantly affect INR control, warfarin management, or adverse events. Our findings suggest that HMOs can safely substitute at least 1 generic formulation of warfarin without extra monitoring.

Subtherapeutic INR values associated with a switch to generic warfarin

OBJECTIVE

To discuss the effect on the international normalized ratio (INR) when patients are converted from therapy with Coumadin to generic warfarin.

CASE SUMMARY

Two cases at a family medicine center anticoagulation clinic in Oklahoma City, OK, in which subtherapeutic INR values occurred after a switch from Coumadin to generic warfarin, while all other variables were kept consistent demonstrate the need for close monitoring of the INR when patients are switched between brands of warfarin.

DISCUSSION

Warfarin is a narrow therapeutic index drug since small changes in systemic concentration can lead to significant variation in phamacodynamic response. In March 1997, the Food and Drug Administration (FDA) approved generic warfare based on the FDA and United States Pharmacopoeia (USP) standards. Due to different specifications between Dupont Pharma and the USP, content uniformity may differ between brand and generic forms of warfarin. United studies have demonstrated bioequivalence between brand and generic. The two cases presented demonstrate the potential for fluctuations in the INR when switching between generic and brand. Thus, these eases illustrate the need for close monitoring if a change is made.

CONCLUSIONS

While considered bioequivalent by the FDA, switching between Coumadin and generic warfarin may lead to significant changes in the INR, warranting dose alterations due to different content uniformity specifications between Dupont Pharma and the USP. Patients switching between Coumadin and generic warfarin should have their INR monitored more carefully.

A randomized, crossover comparison of warfarin products in the treatment of chronic atrial fibrillation

OBJECTIVE

To compare the dosing requirements and international normalized ratios (INRs) associated with two bioequivalent crystalline warfarin sodium products in patients with chronic atrial fibrillation.

METHODS

A multicenter, single-blind (prescriber), randomized, crossover evaluation of Apothecon warfarin and DuPont warfarin (Coumadin) was conducted in consenting adults with chronic or paroxysmal atrial fibrillation who had been receiving DuPont warfarin chronically for the prevention of thromboembolism. Patients were randomly assigned to initially either continue DuPont warfarin or receive Apothecon warfarin for four weeks, with weekly evaluation of dosage and INR changes, safety, and efficacy. Subsequently, patients crossed over and received the other product for four weeks.

RESULTS

There were 113 patients randomized to receive study treatment. Neither the propensity for a dosage change or an INR change nor the magnitude of a dosage change or INR change appeared related to a particular warfarin product (NS for each variable after each study period). After four weeks of treatment, the same number of patients (n = 7) experienced a > or = 20% change in warfarin dosage from the respective baseline with each product. The number of patients with INRs outside the desired protocol range after four weeks of treatment was similar for both groups (< 1.8, n = 9 for both products, or > 3.2, n = 9 for DuPont, n = 10 for Apothecon). No major hemorrhagic or thromboemoblic events occurred.

CONCLUSIONS

The results of this study show that Apothecon warfarin and DuPont warfarin provide equivalent anticoagulation in patients with chronic or paroxysmal atrial fibrillation.

Epistaxis associated with elevation of INR in a patient switched to generic warfarin

A 61-year-old man with atrial fibrillation receiving Coumadin brand warfarin was switched to Barr brand warfarin without his knowledge as a result of a retail pharmacy dispensing error. The patient took the same dosage for 6-7 days and experienced severe epistaxis that required two visits to the emergency room. Previously, his coagulation values were within therapeutic range, but when tested at the emergency room the international normalized ratio was elevated. The patient denied changes in therapy compliance, diet, alcohol ingestion, or use of other drugs. His only other drug, taken periodically, was sildenafil for erectile dysfunction. Clinicians should be aware of differences between branded and generic compounds.