Search Results
The search of relevant databases identified a total of 251 studies. Following title and abstract screening, a total of 213 studies were excluded for not aligning with the prespecified PICO(TSS) criteria. Thirty-eight references were full-text screened, of which 16 did not fit the prespecified criteria for intervention (BA insulin), outcomes (change in HbA1c, fasting glucose, 2-h postprandial glucose, and body weight, insulin dose, hypoglycemia), outcome stratification (data not reported for intervention or comparator), study design (RCTs, phase 2–4), or number of participants (≥ 30 patients per arm), and were therefore excluded. The remaining 22 studies met the PICO(TSS) criteria and were considered for data configuration and included in the meta-analysis [2, 13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33]. A PRISMA flowchart of the study selection process is presented in Fig. 1.
Study Characteristics
A summary of study characteristics is provided in Table 1. A total of 9691 patients were included in the analysis. The most common BA insulin treatments were insulin glargine 100 U/mL (19 studies: [2, 13,14,15, 17,18,19,20,21,22,23,24, 26,27,28,29,30,31,32]) and insulin aspart (11 studies: [15, 16, 18,19,20, 22, 23, 25, 31,32,33]). The patient characteristics in each trial are also reported in Table 1. Fasting plasma glucose ranged from a mean of 5.8 mmol/L (105.1 mg/dL) in insulin glargine 100U/mL + glulisine 0–2×-treated patients [31] to 14 mmol/L (252 mg/dL) in insulin aspart BID + OAD-treated patients [20]. HbA1c levels ranged from a mean of 8.07% in patients who received insulin glargine 100 U/mL + sitagliptin [15] to 11.4% in patients who received insulin glargine 100 U/mL + metformin + sulfonylurea [13].
Quality Assessment
Table S2d in the ESM presents a summary of the quality of the 22 studies. There was generally a low risk of selection bias across the studies, with some studies judged as having an unclear risk of such bias. In eight studies [13, 16, 18, 20, 25, 28, 32, 33], inadequate methods of generating the randomization sequence were reported; similarly, seven studies were judged to have an unclear risk of allocation concealment due to insufficient details [2, 13, 15, 16, 28, 32, 33]. Risk of performance bias (pertaining to the blinding of participants and personnel) and risk of detection bias (pertaining to blinding of outcome assessment) were primarily judged to be high, as most of the studies had an open-label study design. All of the studies had a low risk of attrition and reporting bias. Finally, nearly all the studies had a low risk of other sources of bias.
Primary Efficacy Outcomes (HbA1c)
The primary efficacy outcome of mean change from baseline in HbA1c was reported or calculated in all 22 trials and included in the analysis [2, 13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33]. The MD values for the overall comparisons and for each of the five primary analysis comparisons are reported in Fig. 2a. There was no statistically significant difference in HbA1c change from baseline between patients who used BA regimens and patients who used PM insulin [− 0.04% (95% CI − 0.14, 0.07)], with significant heterogeneity of effect size across the included trails (I2 = 77.4%, p value < 0.05) (Fig. 2a). A comparison of BB insulin 3× to PM insulin BID highlighted a statistically significant difference in HbA1c reduction [− 0.37% (95% CI − 0.64, − 0.10)] (Fig. 2a). In contrast, BA therapy ± OAD led to a similar HbA1c change to that achieved with PM insulin in combination or without OAD [0.00% (95% CI − 0.21, 0.20)], suggesting that the change observed in the BB insulin 3× group resulted from the bolus injections (Fig. 2a). Exploratory analyses were conducted for comparisons based on BA or PM insulin types and patient/trial characteristics, as further summarized in Table S3 of the ESM. When examining PM insulin stratified by type, there was a statistically significant difference in HbA1c reduction between patients on BA insulin regimens and those receiving regular human PM insulin [− 0.39% (95% CI − 0.60, − 0.18)] (Table S4 in the ESM). A secondary analysis of PM insulin ratio also revealed a statistically significant difference in the change in HbA1c between those receiving BA insulin regimens and those receiving PM 50/50 insulin [− 0.22% (95% CI − 0.40, − 0.04)] (Table S4 in the ESM). None of the other secondary analysis comparisons showed statistically significant differences in change from baseline HbA1c (Table S4 in the ESM).
HbA1c ≤ 7% was reported and analyzed in all 22 trials [2, 13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33]. ORs for the overall comparisons and for each of the five primary analysis comparisons are reported in Fig. 2b. Overall, although there were no statistically significant differences between patients who used BA insulin regimens and those who used PM insulin [1.14 (95% CI 0.94, 1.40)], there was significant heterogeneity of effect size across the included trials (I2 = 78.7%, p value < 0.05) (Fig. 2b). The odds of achieving HbA1c ≤ 7% were highest with BB insulin 3× compared to PM insulin BID [1.76 (95% CI 1.17, 2.64)] (Fig. 2b).
Secondary Efficacy Outcomes (Fasting Glucose, 2-h Postprandial Glucose, and Insulin Dose)
Change from baseline in fasting glucose was an average of 0.61 mmol/L smaller in patients who used BA than in patients who used PM insulin regimens [− 0.61 mmol/L (95% CI − 0.90, − 0.32)] (Table 2). Three primary analyses showed statistically significant differences, including BB insulin stepwise versus PM insulin stepwise [− 0.99 mmol/L (95% CI − 1.42, − 0.55)], BB insulin 3× versus PM insulin TID [− 0.74 mmol/L (95% CI − 1.46, − 0.02)], and BA insulin QD ± OAD versus PM insulin BID ± OAD [− 0.59 mmol/L, 95% CI − 1.06, − 0.12)] (Table 2).
Table 2 Secondary efficacy outcomes: analyses of change from baseline in fasting glucose, change from baseline in 2-h postprandial glucose, and total insulin dose at end of follow-up
Although not statistically significant, the evidence suggests that total insulin dose was on average 0.06 U/kg lower in patients who used BA compared to those who used PM insulin [− 0.06 U/kg (95% CI − 0.13, 0.01)] (Table 2). A significant decrease in total insulin dose was reported for the BA insulin QD ± OAD patients compared to the PM insulin BID ± OAD patients [− 0.107 U/kg (95% CI − 0.32, − 0.01)] (Table 2).
An increase from baseline in 2-h postprandial glucose was observed in patients who used BA insulin regimens compared to patients who used PM insulin, but this was not statistically significant [0.09 mmol/L (95% CI − 0.31, 0.49)] (Table 2).
Safety Outcomes (Hypoglycemia and Body Weight)
Total hypoglycemia was suitable for analysis in 19 trials [2, 14,15,16,17,18,19,20,21,22,23,24,25,26,27, 29,30,31, 33]. Results for overall comparisons and each of the five primary analysis comparisons are reported in Fig. 3a. Patients who used BA insulin regimens had a statistically significantly reduced likelihood of total hypoglycemia compared to those who used PM insulin regimens [0.77 (95% CI 0.64, 0.92)], with significant heterogeneity of effect size across the included trials (I2 = 65.3%, p value < 0.05) (Fig. 3a). The only statistically significant difference in hypoglycemia incidence in a primary comparison was between the BA insulin QD ± OAD and PM insulin BID ± OAD groups [0.53 (95% CI 0.40, 0.70)] (Fig. 3a). Other primary comparisons showed no statistical significant difference in hypoglycemia incidence (Fig. 3a). The results of exploratory analyses of total hypoglycemia for comparisons based on BA or PM insulin types and patient/trial characteristics are summarized in Table S5 in the ESM.
Mean change from baseline in body weight was suitable for analysis in 21 trials [2, 13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31, 33], with MDs for overall comparisons and each of the five primary analysis comparisons reported in Fig. 3b. There was a statistically significant difference in body weight between patients who used BA insulin regimens and patients who used PM insulin [− 0.48 kg (95% CI − 0.86, − 0.11)], with significant heterogeneity of effect size across the included trials (I2 = 75.7%, p value < 0.05) (Fig. 3b). The comparison of the BA QD ± OAD and PM insulin BID ± OAD groups showed a significant difference in body weight change [− 1.23 kg (95% CI − 1.99, − 0.47)] (Fig. 3b). Body weight change was also significantly different for BB insulin 1×-treated patients and PM insulin BID-treated patients [− 0.64 kg (95% CI − 1.06, − 0.22)] (Fig. 3b).