Objective: The objective of this study was to: (i) evaluate the potentially inappropriate prescribing (PIP; defined as the use of metformin in the presence of contraindications and/or use in excessive dosage based on the renal function) of metformin in people receiving medication reviews in Australia and (ii) identify the predictors for PIP of metformin.

Method: Retrospective study of patients taking metformin through a large medication review database, containing records between January 2010 and June 2012. Data, including demographics, medical conditions, medications and relevant pathology results, were extracted for analysis. Multivariate logistic regression analysis was used to detect risk factors for PIP of metformin.

Results:

Medication reviews pertaining to 6386 patients who received Home Medicines Reviews (HMRs, n = 5327) or Residential Medication Management Reviews (RMMRs, n = 1059) were included in this study. Overall, there were 12.9% (n = 685) of patients in the HMR group and 17.4% (n = 184) of patients in the RMMR group who had PIP of metformin. Multivariate logistic regression showed age, gender and type of medication review service as the significant (p < 0.05) independent risk factors for PIP of metformin.

Conclusion: Metformin was often used in patients with contraindications, or in higher than recommended dosages in patients with renal impairment. Given the recent debate in the literature about the role of metformin in the presence of contraindications, a detailed prospective study in patients with contraindications and its association with lactic acidosis is warranted to establish the way in which metformin is to be used in these patients.