Improved glycaemic control by switching from insulin NPH to insulin glargine: a retrospective observational study

Abstract

Background: Insulin glargine (glargine) and insulin NPH (NPH) are two basal insulin treatments. This study investigated the effect on glycaemic control of switching from a NPH-based regimen to a glargine-based regimen in 701 patients with type 1 (n= 304) or type 2 (n= 397) diabetes, using unselected primary care data.

Methods: Data for this retrospective observational study were extracted from a UK primary care database (The Health Improvement Network). Patients were required to have at least 12 months of data before and after switching from NPH to glargine. The principal analysis was the change in HbA(1c) after 12 months treatment with glargine; secondary analyses included change in weight and total daily insulin dose. Inconsistent reporting of hypoglycemic episodes precludes reliable reporting of this outcome. Multivariate analyses were used to adjust for baseline characteristics and confounding variables.

Results: After adjustment, both diabetic cohorts showed statistically significant reductions in mean HbA(1c) 12 months after the switch, by 0.38% (p < 0.001) in type 1 patients and 0.31% (p < 0.001) in type 2 patients. Improvement in HbA1c was positively correlated with baseline HbA(1c); patients with baseline HbA(1c) > or = 8% had reductions of 0.57% (p < 0.001) and 0.47% (p < 0.001), respectively. There was no significant change in weight or total daily insulin dose while on glargine. The majority of patients received a basal-bolus regimen prior to and after the switch (mean 79.3% before and 77.2% after switch in type 1 patients, and 80.4% and 76.8%, respectively in type 2 patients, p > 0.05).

Conclusion: In routine clinical practice, switching from NPH to glargine provides the opportunity for improving glycaemic control in diabetes patients inadequately controlled by NPH.

Figure 1

Mean HbA_1c 12 months before and after switching from NPH to glargine (A), mean change in HbA_1c after switch (B), use of bolus insulin before and after switch (C) and total daily insulin dose before and after switch (D) (unadjusted data). The last measurement for NPH is at -3 months (indicated by vertical dotted line). During period -12 m to -3 m patients are taking NPH only. During 3 month switch time point (0 months) patients may be prescribed NPH or glargine. During period +3 m to +12 m patients are only prescribed glargine. Linearly interpolated data were used to graphically depict the change in each parameter. Linearly interpolated data affords a clearer graphical interpretation but may bias estimates of variance; as such error bars (95% confidence intervals for the means) are not reported. Total daily insulin dose was calculated according to the number of units prescribed divided by the number of days covered by the prescription.