Background The adjustment criteria for oseltamivir in patients with renal impairment are different depending on the source consulted. The different criteria lead to different dosage recommendations which are translated into different costs.

Purpose To evaluate the economic impact of different adjustment criteria for oseltamivir in patients with renal impairment.

Material and methods Observational retrospective study of patients treated with oseltamivir during the period 1 December 2014 to 31 March 2015.

All patients hospitalised and treated with oseltamivir were included, except those in haemodialysis treatment. Data collected were: anthropometric data and glomerular filtrate (FG).

Economic evaluation was carried out with the following official information: Tamiflú 75 mg/10 capsules, 31.57€ and Tamiflú 30 mg/10 capsules,17.39€.

Renal impairment posology adjustment criteria were obtained from different databases: technical data of Tamiflú (TD), UptoDate, Micromedex, Sandford Guide to Antimicrobial Therapy 2013 (Sandford), Guía terapéutica antimicrobiana Mensa 2015 (Mensa) and Health Ministry Protocol (HMP). Pill consumption was estimated taking into account our population characteristics and the different adjustments for renal impairment criteria.

Results 31 patients were treated, 100% adults, with a mean age of 66.23 years (64.74–67.71); 45.2% were women. Mean treatment duration was 5.45 (4.4–5.0) days.

Stratificted by renal function: 21/31 patients had FG >60 mL/min, 8/31 had FG=60–30 mL/min and 2/31 had FG=30–10 mL/min.

Two main adjustment criteria groups were found: criteria 1 (TD, Micromedex and UptoDate): FG >60 mL/min 75 mg/12 h; FG= 60–30 mL/min 30 mg/12 h; FG=30–10 mL/min 30 mg/24 h; and criteria 2 (HMP, Mensa, Sandford): FG >60 mL/min 75 mg/12 h, FG >30 mL/min 75 mg/12 h, FG=30–10 mL/min 75 mg/24 h.

Both criteria were different from the FG <60 mL/min recommendation, providing different costs in each case. There were 8 patients with FG=60 mL/min-30 mL/min; following criteria 1, the costs were 139.12€ for 5 days of treatment, following adjustment 2252.56€, which supposes a difference of 113.44€ (44.9% more expensive). Two patients had FG=30–10 mL/min; following criteria 1, the costs were 17.3€ for 5 days of treatment, following criteria 231.57€, which supposes a difference of 14.18€ (44.9% more expensive).

Conclusion Posology adjustment following criteria 1 supposes a saving of 45%. This recommendation was offered by the hospital pharmacy department as it follows TD and is the most cost favourable.

No clinical trials were found to justify adjustment criteria 2.

It is necessary to know the influence of both criteria on treatment and stay duration to obtain a better cost effectiveness evaluation. Our sample did not have enough statistic power to establish differences in duration of stay for the different regimens. Further studies are needed to establish the most efficient adjustment criteria in terms of clinical results.

References and/or Acknowledgements

1. Micromedex. Intelligent information for clinicians (accessed July 2013). http://www.micromedex.com/

2. Mensa J, et al. Guía Terapéutica Antimicrobiana Antares, 2014

References and/or AcknowledgementsNo conflict of interest.