Background and importance Since the first biosimilar drug was authorised, medicine agencies have promoted their use. However, interchangeability or switching are different in each country, creating disparity in their use.

Aim and objectives To measure the use of intravenous biosimilar drugs since their introduction in a third level hospital.

Material and methods We analysed the number of patients treated with biological reference products (BRP) and with their corresponding biosimilars since the arrival of each biosimilar until September 2019. We studied infliximab, rituximab and trastuzumab. Infliximab biosimilar was introduced in September 2015 and rituximab and trastuzumab in August 2018. The results were analysed with Excel.

Results We identified 203 patients treated with infliximab, 16.2% for rheumatoid arthritis (RA) and its derivatives, 80.3% for inflammatory bowel disease (IBD) and 3.5% for other pathologies. A total of 54.7% of patients were treated with a biosimilar, 46.8% as the initial treatment and 7.9% as a switch. All (100%) switches were in patients treated for IBD.

Rituximab was used in 158 patients, 60.8% for different types of haematological cancer, 13.9% for RA, 5.1% for lupus and 20.2% for other diseases. A total of 51.3% of patients were treated with a biosimilar, 36.7% as the initial treatment and 14.6% as a switch. Most (65%) of the switches were found in haematological pathologies. Subcutaneous BRP were given to 29.7% of the total patients.

There were 77 patients treated with trastuzumab, 92.2% for breast cancer and 7.8% for gastric cancer. Of the 71 patients with breast cancer, 59.1% were treated with a biosimilar, 22.5% as the initial treatment and 36.6% as a switch. The remaining 40.9% were treated with subcutaneous BRP. In gastric cancer, 100% of patients were treated with a biosimilar, 66.7% from the beginning and 33.3% as a switch.

Conclusion and relevance The use of biosimilar drugs is more consolidated in new patients and switching is a slower dynamic. The arrival of new biosimilars in the coming years will increase their use. Some medical specialties are more likely to using biosimilar drugs. The presence of a subcutaneous BRP can make the use of biosimilar drugs more difficult as a switch or in new patients as physicians will prescribe a subcutaneous BRP instead of an intravenous biosimilar.

References and/or acknowledgements https://ejhp.bmj.com/content/26/Suppl_1/A133.2

No conflict of interest.