BACKGROUND: The term prediabetes is used to describe a population with an elevated risk of developing type 2 diabetes mellitus (T2DM). With projections of an increase in the incidence of T2DM, prevention or delay of the disease and its complications is paramount. It is currently unknown whether pioglitazone is beneficial in the treatment of people with increased risk of developing T2DM.
OBJECTIVES: To assess the effects of pioglitazone for prevention or delay of T2DM and its associated complications in people at risk of developing T2DM.
SEARCH METHODS: We searched CENTRAL, MEDLINE, Chinese databases, ICTRP Search Portal and ClinicalTrials.gov. We did not apply any language restrictions. Further, we investigated the reference lists of all included studies and reviews. We tried to contact all study authors. The date of the last search of databases was November 2019 (March 2020 for Chinese databases).
SELECTION CRITERIA: We included randomised controlled trials (RCTs) with a minimum duration of 24 weeks, and participants diagnosed with intermediate hyperglycaemia with no concomitant diseases, comparing pioglitazone as monotherapy or part of dual therapy with other glucose-lowering drugs, behaviour-changing interventions, placebo or no intervention.
DATA COLLECTION AND ANALYSIS: Two review authors independently screened abstracts, read full-text articles and records, assessed risk of bias and extracted data. We performed meta-analyses with a random-effects model and calculated risk ratios (RRs) for dichotomous outcomes and mean differences (MDs) for continuous outcomes, with 95% confidence intervals (CIs) for effect estimates. We evaluated the certainty of the evidence with the GRADE.
MAIN RESULTS: We included 27 studies with a total of 4186 randomised participants. The size of individual studies ranged between 43 and 605 participants and the duration varied between 6 and 36 months. We judged none of the included studies as having low risk of bias across all 'Risk of bias' domains. Most studies identified people at increased risk of T2DM by impaired fasting glucose or impaired glucose tolerance (IGT), or both. Our main outcome measures were all-cause mortality, incidence of T2DM, serious adverse events (SAEs), cardiovascular mortality, nonfatal myocardial infarction or stroke (NMI/S), health-related quality of life (QoL) and socioeconomic effects. The following comparisons mostly reported only a fraction of our main outcome set. Three studies compared pioglitazone with metformin. They did not report all-cause and cardiovascular mortality, NMI/S, QoL or socioeconomic effects. Incidence of T2DM was 9/168 participants in the pioglitazone groups versus 9/163 participants in the metformin groups (RR 0.98, 95% CI 0.40 to 2.38; P = 0.96; 3 studies, 331 participants; low-certainty evidence). No SAEs were reported in two studies (201 participants; low-certainty evidence). One study compared pioglitazone with acarbose. Incidence of T2DM was 1/50 participants in the pioglitazone group versus 2/46 participants in the acarbose group (very low-certainty evidence). No participant experienced a SAE (very low-certainty evidence).One study compared pioglitazone with repaglinide. Incidence of T2DM was 2/48 participants in the pioglitazone group versus 1/48 participants in the repaglinide group (low-certainty evidence). No participant experienced a SAE (low-certainty evidence). One study compared pioglitazone with a personalised diet and exercise consultation. All-cause and cardiovascular mortality, NMI/S, QoL or socioeconomic effects were not reported. Incidence of T2DM was 2/48 participants in the pioglitazone group versus 5/48 participants in the diet and exercise consultation group (low-certainty evidence). No participant experienced a SAE (low-certainty evidence). Six studies compared pioglitazone with placebo. No study reported on QoL or socioeconomic effects. All-cause mortality was 5/577 participants the in the pioglitazone groups versus 2/579 participants in the placebo groups (Peto odds ratio 2.38, 95% CI 0.54 to 10.50; P = 0.25; 4 studies, 1156 participants; very low-certainty evidence). Incidence of T2DM was 80/700 participants in the pioglitazone groups versus 131/695 participants in the placebo groups (RR 0.40, 95% CI 0.17 to 0.95; P = 0.04; 6 studies, 1395 participants; low-certainty evidence). There were 3/93 participants with SAEs in the pioglitazone groups versus 1/94 participants in the placebo groups (RR 3.00, 95% CI 0.32 to 28.22; P = 0.34; 2 studies, 187 participants; very low-certainty evidence). However, the largest study for this comparison did not distinguish between serious and non-serious adverse events. This study reported that 121/303 (39.9%) participants in the pioglitazone group versus 151/299 (50.5%) participants in the placebo group experienced an adverse event (P = 0.03). One study observed cardiovascular mortality in 2/181 participants in the pioglitazone group versus 0/186 participants in the placebo group (RR 5.14, 95% CI 0.25 to 106.28; P = 0.29; very low-certainty evidence). One study observed NMI in 2/303 participants in the pioglitazone group versus 1/299 participants in the placebo group (RR 1.97: 95% CI 0.18 to 21.65; P = 0.58; very low-certainty evidence). Twenty-one studies compared pioglitazone with no intervention. No study reported on cardiovascular mortality, NMI/S, QoL or socioeconomic effects. All-cause mortality was 11/441 participants in the pioglitazone groups versus 12/425 participants in the no-intervention groups (RR 0.85, 95% CI 0.38 to 1.91; P = 0.70; 3 studies, 866 participants; very low-certainty evidence). Incidence of T2DM was 60/1034 participants in the pioglitazone groups versus 197/1019 participants in the no-intervention groups (RR 0.31, 95% CI 0.23 to 0.40; P < 0.001; 16 studies, 2053 participants; moderate-certainty evidence). Studies reported SAEs in 16/610 participants in the pioglitazone groups versus 21/601 participants in the no-intervention groups (RR 0.71, 95% CI 0.38 to 1.32; P = 0.28; 7 studies, 1211 participants; low-certainty evidence). We identified two ongoing studies, comparing pioglitazone with placebo and with other glucose-lowering drugs. These studies, with 2694 participants. may contribute evidence to future updates of this review.
AUTHORS' CONCLUSIONS: Pioglitazone reduced or delayed the development of T2DM in people at increased risk of T2DM compared with placebo (low-certainty evidence) and compared with no intervention (moderate-certainty evidence). It is unclear whether the effect of pioglitazone is sustained once discontinued. Pioglitazone compared with metformin neither showed advantage nor disadvantage regarding the development of T2DM in people at increased risk (low-certainty evidence). The data and reporting of all-cause mortality, SAEs, micro- and macrovascular complications were generally sparse. None of the included studies reported on QoL or socioeconomic effects.
