The aim was to compare the prescribed and calculated daily insulin dosages based on prescription data in type 2 diabetes patients in a general practice database.Methods:
A total of 17 782 type 2 diabetes patients (age: 70.0 ± 11.5 years; 52% males; 16% diabetologist care) with ≥2 insulin prescriptions from 834 practices were analyzed (Disease Analyser: 01/2011-12/2015). Prescribed daily dosage (PDD) (physician documentation) and calculated daily dose (CDD) (pack size × strength × volume / days between 2 prescriptions) were calculated for short-acting, long-acting, and premixed insulins. PDD and CDD were compared using paired t-tests. Linear regression models assessed the associations of insulin dosage difference (CDD-PDD) with age, sex, diabetologist care, private health insurance, obesity, HbA1c, hypertension, hyperlipidemia, macro- and microvascular complications.Results:
Mean [SD] CDDs were higher than PDDs for short-acting (52  vs 48  units/day), long-acting (30  vs 24  units/day), and premixed (46  vs 40  units/day) insulins (all P < .05). In regression models, age (per year) was associated with higher CDD-PDD differences (+0.11, +0.04, +0.10; P < .01) for short-, long-acting, and premixed insulins, respectively. Diabetologist care was related to lower differences (–2.92, –1.02, –3.65; all P < .05). HbA1c was associated with higher differences in long-acting and premixed insulins, but was related to a lower difference in short-acting insulins (all P < .05).Conclusions:
CDD in primary care database studies substantially overestimate the PDD (8-25%). Age, diabetologist care, and glycemic control were related to CDD-PDD differences. Priming and safety shots with pens, dosing errors, or the accumulation of insulin reserves by patients may be underlying reasons.