An assessment of the accuracy of NovoPen 1 delivery after prolonged use.

Forty-five NovoPen 1 injection devices have been assessed for accuracy of insulin delivery. Twenty-six pen-injectors had been returned either because the device had developed structural faults or the patients had experienced unexpected deterioration in diabetic control. Twelve of these pen-injectors were unusable. The remaining 14 pen-injectors ('faculty pen-injectors') were assessed by measuring the weight of insulin solution delivered in each of 10 depressions of the plunger and compared with similar measurements from 10 unused pen-injectors ('new pen-injectors') and 9 pen-injectors ('used pen-injectors') which had been used uneventfully for greater than 3 years. New pen-injectors delivered insulin solution with an accuracy (median error) of 2.8% and reproducibility (median SD) of 2.0%. Used pen-injectors had an accuracy of 2.3% and reproducibility of 3.5%. The 14 suspect pen-injectors ('faculty pen-injectors') demonstrated an accuracy of 2.8% with reproducibility of 4.0%. The reduction in reproducibility was due to faults in 4 pen-injectors, 2 of which consistently delivered less insulin than expected, while a further two pen-injectors were intermittently inaccurate.