Background Adding new drugs to the hospital formulary affects outpatient prescribing greatly in secondary care. Ambulatory rivaroxaban was included in the hospital formulary in November 2010 for approved indications only.

Purpose To assess the effect on the prescription of ambulatory rivaroxaban for restricted use for approved indications: prevention of venous thromboembolism in patients adults undergoing elective hip or knee replacement.

Materials and methods Analysis of prescription data by prescription, supplied by the Pharmaceutical Inspection of the Health Management Area, during the 5 months prior to the inclusion of the drug in the formulary (June to October 2010) and the subsequent 5 months (November 2010 to March 2011). The following data were collected: number of patients treated with rivaroxaban, number of prescriptions dispensed per patient, number of defined daily doses (DDD) per patient, duration of treatment and prescribing physician's specialty.

Results During the 5 months prior to the inclusion of the drug in the formulary, five patients received a total of eight prescriptions for rivaroxaban in pharmacies, whereas after 5 months, 32 patients collected the prescribed drug a total of 48 times. The authors note that both the number of prescriptions and patients increased by 600% after the inclusion of rivaroxaban in the formulary. The prescribing physician was a specialist in traumatology in 31 of the 37 cases (84%). The remaining six (16%) were prescribed by a specialist in urology; with these patients the drug could have been used in conditions other than those approved. It was further found that seven patients (19%) were dispensed a total number of DDD that exceeded the time required for the recommended treatment by clinical indications.

Conclusions Inclusion of rivaroxaban in the formulary had a clear impact on outpatient prescription in our health area, with specialist drugs significantly affecting prescriptions in secondary care. It is important to assess the fundamental impact that might result from prescriptions for it, before including a new drug in the formulary. Once included, extra monitoring is important to minimise discrepancies between the approved indication and the way the drug is prescribed.