title: Adherence to premixed insulin in a prefilled pen compared with a vial/syringe in people with diabetes in Singapore.
abstract: BACKGROUND
  The real-world clinical effectiveness of exogenous insulin is limited by nonadherence. Various insulin delivery systems have been developed to help improve adherence, with prefilled pens gaining popularity among adult Singaporeans with diabetes. However, adherence to insulin in people with diabetes in Singapore and most of Asia has not been studied.
  
  
  OBJECTIVE
  This study aimed to compare adherence to premixed insulin formulated in a prefilled pen versus a vial/syringe and to identify predictors of adherence in 955 patients managed at the outpatient clinics of the largest acute care hospital in Singapore.
  
  
  METHODS
  In this retrospective longitudinal study, electronic medical and pharmacy refill records were used to determine adherence to insulin over 24 months, measured in terms of compliance and persistence. Compliance is expressed as the medication possession ratio (used as continuous and categorical variables), and persistence is reported as a dichotomous variable with a permissible refill gap of 30 days before discontinuation of therapy is considered. Multivariate linear or logistic regression analysis was used to identify predictors of adherence.
  
  
  RESULTS
  Compared with prefilled pen users, vial/syringe users were older (mean [SD] age, 64.1 [10.6] vs 62.4 [11.9] years; P = 0.032), and more were undergoing polypharmacy (69.6% vs 54.1%; P < 0.001). The mean (SD) medication possession ratio was comparable in vial/syringe versus prefilled pen users (83.8% [26.9%] vs 86.0% [23.2%]; P = 0.266). Prefilled pen users were more persistent with therapy compared with vial/syringe users (odds ratio = 1.36; 95% CI, 1.01-1.86) after adjusting for sociodemographic and clinical covariates. Median time to discontinuation of therapy was comparable (vial/syringe vs prefilled pen: 409 vs 532 days; P = 0.076). Being managed by an endocrinologist and not receiving government subsidies were significant predictors of persistence.
  
  
  CONCLUSIONS
  Compared with other studies that found strong associations between adherence and insulin devices, the findings of this study suggest that persistence but not compliance varies by insulin device. The willingness to pay for health care, in addition to affordability, may affect insulin therapy adherence. Patients with uncontrolled diabetes due to suspected nonadherence may benefit from referral to a multidisciplinary care team comprising endocrinologists, diabetes nurse educators, dietitians, and allied health professionals. These findings are applicable to outpatients with similar demographic features managed at other acute care hospitals in Singapore. The impact of insulin devices on glycemic control needs to be investigated in future larger studies.
authors.affiliation: Department of Pharmacy, Singapore General Hospital, Singapore; Department of Pharmacy, Faculty of Science, National University of Singapore, Singapore.
authors.forename: Hua Heng McVin
authors.initials: HH
authors.lastname: Cheen
authors.affiliation: Department of Pharmacy, Singapore General Hospital, Singapore.
authors.forename: Seng Han
authors.initials: SH
authors.lastname: Lim
authors.affiliation: Department of Biological Sciences, Faculty of Science, National University of Singapore, Singapore.
authors.forename: Ming Chien
authors.initials: MC
authors.lastname: Huang
authors.affiliation: Department of Endocrinology, Singapore General Hospital, Singapore.
authors.forename: Yong Mong
authors.initials: YM
authors.lastname: Bee
authors.affiliation: Department of Pharmacy, Faculty of Science, National University of Singapore, Singapore. Electronic address: phawhl@nus.edu.sg.
authors.forename: Hwee Lin
authors.initials: HL
authors.lastname: Wee
mesh_terms: D000368:Aged; D003924:Diabetes Mellitus, Type 2 / Q000188:drug therapy*; D004209:Disposable Equipment; D005260:Female; D006801:Humans; D007004:Hypoglycemic Agents / Q000008:administration & dosage* / Q000627:therapeutic use; D007267:Injections / Q000295:instrumentation; D007328:Insulin / Q000008:administration & dosage* / Q000627:therapeutic use; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D012846:Singapore; D013223:Statistics as Topic; D013594:Syringes / Q000706:statistics & numerical data; D016903:Drug Monitoring
chemical_list: D007004:Hypoglycemic Agents; D007328:Insulin
keywords: compliance; diabetes mellitus; insulin; medication adherence; persistence