Indications and associated factors for prescribing intravenous iron supplementation in Swiss general practice: a retrospective observational study

BACKGROUND: Intravenous iron supplementation (IVIS) is increasing in Swiss general practice. This is controversial because of higher costs and risks compared with oral iron supplementation (OIS). In this study, we aimed to investigate indications for OIS and IVIS in Swiss general practice and test which factors are associated with prescribing IVIS instead of OIS. METHODS: This was a retrospective observational study using data from electronic medical records of 279 Swiss general practitioners (GPs), including all their patients at their first OIS and IVIS administration who were at least 14 years old and with available pretreatment serum ferritin and haemoglobin measurements. We also collected data about the following comorbidities: chronic kidney disease (CKD) stage 3b or higher, inflammatory bowel disease (IBD), chronic heart failure and restless legs syndrome. Outcomes were proportions of cases treated with IVIS or OIS by assumed indication (anaemic or non-anaemic iron deficiency [NAID]) or the abovementioned comorbidities. We evaluated associations with IVIS prescription using regression models adjusting for patient and GP variables. RESULTS: We assessed 1282 IVIS and 3003 OIS cases (median age 44 and 40 years, female in 86.7 and 88.6%, respectively). The most important indication for both IVIS and OIS was NAID (59.4 and 74.7%, respectively). Significant associations with prescribing IVIS instead of OIS were the severity of iron deficiency (reflected by serum ferritin levels and the presence of anaemia), the presence of advanced CKD, IBD and male sex of the GP. There was a time trend towards increasing serum ferritin levels associated with initiation of IVIS in NAID. CONCLUSION: When preferring IVIS to OIS, Swiss GPs seem to consider severity of iron deficiency and comorbid conditions. However, pretreatment serum ferritin levels in IVIS for NAID are increasing, suggesting an ongoing indication extension and potential overuse.