Garvey WT, Ryan DH, Henry R, et al. Prevention of type 2 diabetes in subjects with prediabetes and metabolic syndrome treated with phentermine and topiramate extended release. Diabetes Care 2014;37:912–21.
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Objective. To determine the effect of phentermine and topiramate extended release (PHEN/TPM ER) treatment on progression to type 2 diabetes and/or cardiometabolic disease in subjects with prediabetes and/or metabolic syndrome (MetS) at baseline.
Design. Sub-group analysis of a larger double-blind, randomized, placebo-controlled trial of PHEN/TPM ER in overweight and obese adults.
Setting and participants. The larger study had 2 phases —a 56-week weight loss trial (CONQUER, n = 866), followed by an extension of the drug trial out to 108 weeks (SEQUEL, n = 675) in a sub-group of CONQUER participants. The CONQUER trial, based at 93 U.S. centers, enrolled overweight or obese patients with at least 2 obesity-related comorbidities and randomly assigned them to receive either placebo or PHEN/TPM ER at a lower (7.5 mg/46 mg) or higher (15 mg/92 mg) daily dose. All 3 groups also received lifestyle modification counseling that included an evidence-based diet and exercise curriculum. Participants received study drug and lifestyle counseling in the setting of monthly visits during the 60- (CONQUER) or 108-week (SEQUEL) follow-up period.
The analyses presented in this paper focus on the 475 participants who completed both CONQUER and SEQUEL and who were characterized as pre-diabetic or as having the metabolic syndrome (MetS) at baseline. Pre-diabetes was defined as having a blood glucose level of 100–125 mg/dL or higher while fasting, or 140–199 mg/dL after an oral glucose tolerance test (GTT). MetS was characterized in participants who displayed 3 or more of the following at baseline: waist circumference ≥ 102 cm in men or 88 cm in women; triglycerides ≥ 150 mg/dL or on a lipid-lowering medication; HDL < 40 mg/dL in men or < 50 mg/dL in women; systolic BP ≥ 130 mm Hg or diastolic BP ≥ 85 mm Hg (or on antihypertensive); and fasting glucose ≥ 100 mg/dL or on treatment for elevated glucose.
Main outcome measures. The primary outcome for this study was percent weight loss at 108 weeks of follow-up (or early termination). Secondary outcomes included cardiometabolic changes, such as development of type 2 diabetes and changes in lipid measures, blood pressure, and waist circumference. These were assessed at baseline, week 56, and week 108 (or at early termination). Rates of progression to type 2 diabetes were compared between the treatment groups using chi-square testing. Intention-to-treat (ITT) ANCOVA analysis was performed with multiple imputation techniques to address missing data, as well as with an alternative analysis using last observation carried forward.
Results. The study arms were similar with respect to baseline characteristics. Average age was 51 years in the high dose PHEN/TPM ER arm and 52 in the other arms. Over half (65%) of participants were women and 86% were Caucasian. Mean BMI was 36 kg/m2 (class II obesity). Over half of participants were on antihypertensive medications at baseline but with well-controlled blood pressure (mean 128/80 mm Hg). Of the 475 people in this analysis, 316 met criteria for prediabetes, 451 for MetS, and 292 for both prediabetes and MetS.
Weight loss at 2 years was significantly greater in subjects taking PHEN/TPM ER (10.9% in the lower dose group, 12.1% in the higher dose group) compared to those taking placebo (2.5%) (P < 0.001). Mirroring weight loss results, type 2 diabetes incidence was also significantly lower in the drug treatment arms than in the placebo arm at 2 years after randomization—annualized incidence was 6.1% for placebo vs. 1.8% for lower-dose drug and 1.3% for higher-dose drug (P < 0.05). Greater weight loss was associated with greater decrease in diabetes incidence across all 3 arms of the study. Those persons who did not achieve at least a 5% weight loss at 2 years had the highest annualized risk of developing diabetes (6.3%), compared with a 0.9% risk among those who lost at least 15% of their weight. Improvements in other cardiometabolic parameters, including HDL, triglycerides, waist circumference, and insulin sensitivity index, was more common among the PHEN/TPM ER participants compared with placebo. Blood pressure decreased slightly for all 3 groups and there was no significant difference between the drug arms and the placebo arm.
Discontinuation of study medication occurred in all 3 groups (3.1% in placebo, 6.1% in lower-dose medication, and 5.5% in higher-dose medication), with serious adverse events in 5%, 7%, and 8.5%, respectively. There were no deaths.
Conclusion. PHEN/TPM ER administered over a 2-year period significantly improved weight loss and decreased progression to type 2 diabetes relative to placebo in a group of at-risk participants.
Diabetes and related cardiometabolic disease are major contributors to morbidity and mortality in adults. With the exception of invasive treatments such as bariatric surgery, reversal of diabetes once it is established has proven quite difficult [1,2], and thus there is an increased emphasis from the public health and medical communities on preventing the development of this disease in the first place. Complicating the picture, recently broadened criteria for pre-diabetes will likely result in a very large number of these at-risk individuals being identified [3,4]. Although intensive lifestyle interventions resulting in a 5% to 7% weight loss among pre-diabetics have been shown to delay progression to diabetes , the translation of these programs into real-world settings has, so far, shown less promise than the original randomized trials might have indicated . Although there is ongoing work to try to improve results and uptake in community-based lifestyle intervention programs, for many patients and clinicians these resource-intensive programs currently prove difficult to do well on a large scale.
Alternative methods of helping patients achieve and maintain that critical > 5% weight loss are desperately needed, not only for preventing diabetes, but also for impacting the numerous other risks associated with obesity. This particular trial capitalized on the notion that it is probably successful weight loss, not the intervention format used to achieve that weight loss, which drives decreased diabetes risk. This study was a sub-analysis of a larger randomized trial, and many of the strengths of that larger study are therefore reflected in this paper. Participants and study staff were blinded to treatment arm with the use of placebo, a very important strength when adverse reactions and drug intolerances need to be measured. Furthermore, this likely equalized motivation to comply with the lifestyle recommendations across the treatment arms—this might not have been the case if patients were aware that they were or were not receiving study drug. Another key strength of the study is its duration. PHEN/TPM ER is unique in that it is approved by the FDA for long-term use. Whereas many studies of weight loss show maximum intervention effect at about 6 months followed by weight regain, this study showed sustained weight loss up to 2 years after starting therapy, presumably because participants could actually continue the therapy for the full 2 years. Most importantly, the intervention itself (medication plus low-intensity lifestyle counseling) is likely highly replicable in clinical practice.
There are some important limitations to consider when interpreting the results from this study. First, the participants analyzed in this paper were comprised entirely of people who had already participated in a full year of the parent study and therefore probably represent a sub-group that might have been experiencing greater success as a result of their participation, potentially generating an overly optimistic estimate of weight loss and health effect for all of the groups relative to what might be seen in a general population. This feature of the design also limits this study’s ability to comment on drug intolerance or early adverse reactions—those who didn’t stick with the pills for at least a year would not have been included in these analyses. In terms of generalizability, although the infrastructure required from a clinical standpoint is much lower for an intervention like this (prescribing a medication) compared to an intensive lifestyle intervention, these drugs are still costly, and many insurers/providers may not offer them on formulary. Thus, to realize the long-term benefits of sustained weight loss, patients may need to face significant out-of-pocket costs, which may limit uptake of this therapy to those with financial means. For this and other reasons, it will be important to do future studies looking at how quickly weight is re-gained once people stop taking the medication. Another threat to generalizability is the racial makeup of the participants—the vast majority of them were non-Hispanic white. Furthermore, although a majority of the participants had hypertension, it was well-controlled in all (a prerequisite for taking the medication), and it is unclear whether in a real-world patient population hypertension would be adequately controlled in a large number of patients.
Another issue to consider when looking at the use of weight loss medications for prevention of diabetes is the relative risk of prolonged medication use compared with the risk for developing diabetes. Clearly, for obese patients who are interested in losing weight for other reasons, prevention of diabetes is a wonderful side effect of achieving that goal. However, it is worth noting that even in the highest-risk group of participants in this study (those who lost < 5% of weight), the annualized risk of developing diabetes was about 6% (< 20% cumulative risk projected over 3 years). Compare this to the 7% to 8% serious adverse event rate observed in those on drug therapy. Although the medication did reduce annualized diabetes risk significantly, the vast majority of people in all the arms did not develop diabetes during follow-up. This drives home the point that our current categorization of pre-diabetes is far from perfect in identifying people who are at imminent risk of becoming diabetic, and reinforces the notion that any treatment we provide to them in the name of diabetes prevention should be free from risk of harm. Rather than applying a long-term medication with potentially harmful side effects to a large group of at-risk patients, more research is needed to provide tools for clinicians to think carefully about which of their patients are truly at highest risk of going on to develop diabetes in the near future.
Applications for Clinical Practice
Although clinicians ought not use PHEN/TPM ER exclusively for diabetes prevention based on the results from this trial, delay of diabetes onset is a possible and important benefit of the use of PHEN/TPM ER in obese patients, provided that they are willing to also make and sustain lifestyle changes in order to lose a clinically significant amount of weight.
—Kristina Lewis, MD, MPH
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