Background Orphan drugs have a high economic impact with a small number of patients. In recent years their prescription has significantly increased.

Purpose To describe and to analyse the evolution of expenditure on orphan drugs according to the diagnosis.

Material and methods Retrospective study that includes all the patients for whom orphan drugs have been dispensed from January 2014 to December 2016. The parameters specified were: number of patients per drug, per diagnosis and per economic expenditure(€), and percentage of total expenditure and annual expenditure. The data were obtained from the optimised computerised order entry ATHOS^® software and collected in an Excel^® database designed for this purpose.

Twenty-seven active substances were identified The number of patients was 252, 279 and 295 in the years 2014, 2015 and 2016 respectively, with a total expenditure of €16.219,960 that was distributed in 29%, 33% and 38% respectively. The diagnoses that supposed a greater expense (% of annual expense) were: metabolic disease 33%, 34%, 37%; multiple myeloma 20%, 22%, 23%; oncologic disease 16%, 18%, 22%; pulmonary hypertension 20%, 15%, 5%; and paroxysmal nocturnal haemoglobinuria 7%, 6%, 6%.

The percentage of patients in relation to the diagnosis was constant during the three years, being that oncology and multiple myeloma presented the highest number of patients (38%), followed by pulmonary hypertension (6.3%) and metabolic disease (1.9%).

With regard to the total expenditure of three years, metabolic diseases accounted for 35%, multiple myeloma 22%, oncology diseases 19%, pulmonary hypertension 13% and paroxysmal nocturnal haemoglobinuria 6%.

Regarding drugs, lenalidomide accounted for 21% of total expenditure, followed by agalsidase alfa with 12%, alglucosidase alfa 7%, eculizumab 6%, nilotinib 5% and brentuximab 2%.

Regarding the average expenditure per patient/year, paroxysmal nocturnal haemoglobinuria entailed a cost per patient of €317.808, followed by metabolic disease with €118.326, multiple myeloma €20.119 and oncology disease €4.075.

Spending on orphan drugs was approximately 15% of the total hospital pharmacy consumption.

Conclusion In the last three years, the number of patients with prescribed orphan drugs has increased, with a rise of €1.3 million.

Metabolic diseases are one of the biggest expenses every year, with a very small number of patients and a high cost per patient/year.

No conflict of interest