Adherence to metformin is reduced during school holidays and weekends in children with type 1 diabetes participating in a randomised controlled trial

Background: Non-adherence to treatment in childhood chronic illness has serious consequences for health and healthcare costs. Accurate detailed objective data on adherence are minimal in this age group.

Objective: To evaluate medication adherence using electronic monitoring systems in children with type 1 diabetes (T1D).

Design: A cohort study of 90 T1D children (aged 13.6±2.5 years, 41 males) from two paediatric diabetes clinics, participated in a 12-month double-blind, randomised, placebo-controlled trial (1:1 allocation). This cohort provided 28 336 days of study observations; 7138 school holiday and 8875 weekend/public holiday days.

Method: Adherence to intervention (metformin (n=45) or placebo (n=45)) was measured objectively by Medication Event Monitoring Systems (MEMS) including proportion of medication doses taken and daily adherence patterns and by tablet count at 3, 6 and 12 months. The trial was completed in June 2015.

Results: There was an average (SD) of 363.3 (42) days of MEMS observations available for each study participant (94.1 (12.6) school holiday days and 117.1 (13.4) weekend/public holiday days). Adherence reduced during school holidays (adjusted OR (aOR) 0.81; 95% CI 0.72 to 0.91; p<0.001) and during weekends/public holidays (aOR 0.74; 95% CI 0.69 to 0.80; p<0.001). Adverse effects to the intervention did not affect overall adherence (aOR 0.77; 95% CI 0.3 to 2.01; p=0.6). Age, gender, body mass index, diabetes duration, insulin dose, HbA1c (Haemoglobin A1c) or socioeconomic status did not predict adherence.

Conclusion: Medication adherence was reduced during school holidays and on weekends in children with T1D. Clinical characteristics including socioeconomic status and the presence of adverse effects did not predict adherence.

Trial registration number: ACTRN12611000148976.