Background Overweight and obesity lead to increased healthcare costs because of the high prevalence of associated diseases. There are drugs of high economic impact that are dosed by weight. Infliximab is a drug whose dosage is indicated as 3 mg/kg (rheumatoid arthritis) or 5 mg/kg (other indications).

Purpose To determine the prevalence of overweight and obesity in patients treated with infliximab. To calculate the annual increase in treatment costs as a result of the prevalence of overweight and obesity.

Material and methods Retrospective, cross sectional study. Data on sex, age, diagnosis, prescribed dose and dispensations between January and December 2014 were collected. Dosage was established as indicated in the European Public Assement Report (EPAR) for Remicade (prescribed dose/dose indication (3ó5 mg/kg)=weight); from that premise, the weight of each patient was calculated. Estimated size was collected from the Spanish National Statistics Institute, according to sex and age. Estimated body mass index (BMI) was calculated. It was established that overweight was BMI 25–29.9 kg/m² and obesity was BMI >30. The cost of treatment per dose naturally weighted and cost of treatment with recommended weight per dose were calculated, the difference between both costs and the average percentage increase were also calculated. Each incremental cost per patient was multiplied by the number of dispensations to meet the total additional cost for overweight or obesity treatment with infliximab in 2014. The recommended weight was maintained that weight BMI 24.9. Data were analysed using the SPSS v.20.

Results 156 patients were enrolled and 58% were men. Average age was 47 years. 41.6% of the sample had a BMI >25. 20.5% were overweight and 21.1% were obese. In patients who were overweight or obese, treatment costs increased by 27.29% on average. The 2014 annual additional cost associated with overweight and obesity treatment with infliximab was 121 242.18€.

Conclusion The prevalence of overweight and obesity among patients treated with Infliximab was close to 45%; this increases the cost of treatment by more than 25% of the total cost of treatment. Overweight and obesity could be regarded as an economic impact factor for drugs which are dosed by weight. The Pharmacy and Therapeutics Committee must establish the most cost efficient drug by BMI for different indications studied and design a protocol.

No conflict of interest.