Placebo-controlled trials in type 2 diabetes

Magnitude and Pattern of Placebo Response in Clinical Trials of Oral Antihyperglycemic Agents: Data From the U.S. Food and Drug Administration, 1999-2015

OBJECTIVE

To evaluate the magnitude of placebo response and treatment response patterns in clinical trials of investigational oral antihyperglycemics over time.

RESEARCH DESIGN AND METHODS

We examined the U.S. Food and Drug Administration medical and statistical reviews for 19 oral antihyperglycemic agents (23,438 patients, 50 trials, and 96 treatment arms) approved between 1999 and 2015. Placebo and medication treatment response (HbA_1c reduction) and effect sizes were examined over time (year of approval). Exclusively placebo-controlled and augmented/adjunctive placebo-controlled trials were analyzed separately, and differences were compared. Potential effects of trial and patient characteristics were explored.

RESULTS

In more recent trials, augmented placebo-controlled arms reduced HbA_1c by 0.2% on average and more frequently lowered HbA_1c from baseline compared with exclusively placebo-controlled arms (63 vs. 18%; χ² = 9.93; P = 0.002). In exclusively placebo-controlled trials, placebo response increased significantly over time (β = 0.035; R² = 0.31; P = 0.0013), reaching ∼0% average change in HbA_1c, whereas drug response also increased significantly (β = 0.017; R² = 0.076; P = 0.0498). In augmented placebo-controlled trials, placebo response (β = 0.33; R² = 0.407; P < 0.001) showed the same pattern, whereas the growth in drug response was not significant (R² = 0.031; P = 0.207). Placebo response in both groups increased by 0.5% HbA_1c reduction over time, whereas effect sizes remained stable with high success rates (100%; 96 out of 96). Drug response and effect size were not significantly predicted by patient or trial characteristics, but follow-up analysis suggested an inverse relationship of placebo baseline HbA_1c with placebo response.

CONCLUSIONS

Remarkably, placebo-treated patients with diabetes commonly experienced reduction in HbA_1c, more markedly in augmented compared with exclusively placebo-controlled treatment arms. Placebo response increased significantly over time without impacting efficacy outcomes. Nonpharmacologic effects measured in the placebo response appear stronger when used with active medication than when implemented in isolation and may be related to the level of HbA_1c at baseline.

Physicians' preferences for active-controlled versus placebo-controlled trials of new antihypertensive drugs

OBJECTIVE

To evaluate physicians' preferences for referring patients to, and using information from, active-controlled trials (ACTs) versus placebo-controlled trials (PCTs) of new antihypertensive drugs.

DESIGN AND SETTING

Nationwide mailed survey, with telephone contact of nonresponders to assess nonresponse bias.

PARTICIPANTS

One thousand two hundred primary care physicians randomly selected from the American Medical Association's Master File. Of 1,154 physicians eligible to respond, 651 (56.4%) returned completed questionnaires.

MEASUREMENTS AND MAIN RESULTS

We measured physicians' stated willingness to encourage hypertensive patients to enroll in ACTs and PCTs of new antihypertensive drugs, their views of the relative merits of ACTs versus PCTs, their stated willingness to prescribe new drugs tested in ACTs or PCTs, and their views regarding the overall justifiability of the 2 designs. Physicians were significantly more likely to indicate they would encourage their patients to enroll in ACTs than in PCTs (P <.0001). Physicians thought ACTs provided more valuable information for their practices, were more likely to lead to a public health benefit, offered enrolled patients greater opportunity for personal benefit, and were less likely to expose enrolled patients to unnecessary risks (all P <.0001). Physicians were more likely to prescribe new drugs that had been compared in ACTs (P <.0001), and viewed ACTs as a more justifiable method for testing new antihypertensive drugs (P <.0001). There was no evidence of nonresponse bias for these main results.

CONCLUSIONS

Although PCTs remain the standard method for testing new antihypertensive drugs, physicians strongly prefer ACTs. Using ACTs to test new antihypertensive drugs may enhance the efficiency of patient recruitment and more strongly influence physicians' prescribing practices.