Background Omnitrope (somatropin) was the first bi-osimilar approved by the European Medicine Agency in 2006. Since somatropin is one of the biological products most commonly prescribed to children and adolescents, a study was performed with the aim to evaluate the pre-scription of this drug in the Italian paediatric population. To the best of our knowledge, no drug utilisation studies evaluated the prescription profile of biosimilars in the pe-diatric population.

Methods Data collected in healthcare administrative databases of Lombardy region, Italy, in the 2004–2012 period were analysed. Children and adolescents who received prescriptions of somatropin (H01AC01code of the Anatomical Therapeutic Chemical classification sys-tem) for at least two consecutive years were identified as prevalent cases. Subjects were defined incident cases if they had no somatropin prescriptions in the previous 2 years. Prevalence and incidence of somatropin prescrip-tion were estimated by gender, age group and observa-tion year. Moreover, each youth with the first prescrip-tion (index prescription, IP) in the 2006–2010 period was monitored for 24 months, and somatropin prescriptions were analysed to evaluate if a switch between products occurred. In switchers, the occurrence of specialist vis-its and/or hospitalizations in the 60 days preceding the change was checked.

Results During 2012, the prevalence of somatropin pre-scription in Lombardy region was 12.0 per 10,000, with an incidence of 2.8 per 10 000. Both prevalence and inci-dence increased across time (from 9.6 and 1.6 per 10 000 in 2004, respectively). The prevalence was greater in boys than in girls (14 versus 10 per 10,000), and increased with increasing age (from 2.7 in pre-schoolers to 21.1 per 10 000 in adolescents). A total of 1415 children had the somatro-pin index prescription in the 2006–2010 period. Only 98 of them (7%) started with the biosimilar Omnitrope. The percentage of children starting with the biosimilar slightly increased with increasing age, from 4.9% in the 1–5 years old to 7.5% in the adolescents. In all, 17 out of the 98 sub-jects (17.3%) with biosimilar as IP switched to another so-matropin product during the 24 months after the starting date. Of the 1317 children who started with a ‘branded’ somatropin, 47 (3.6%) switched to another products (no one to Omnitrope). The rate of switch was higher in pre-school aged children (3 out of 10) and decreased with in-creasing age (5 out of 45 in adolescents). On the contrary, the frequency of switch in subjects with other somatropin products did not change among age groups.

Only 4 out of 17 subjects had a specialist visit and/or an hospitalisation in the 60 days before the switch from bio-similar to ‘branded’ products, while in the non-biosimilar group, a specialist visit and/or hospital admission was re-corded for 26 out of 47 children.

Conclusion Only 7% of incident (naïve) cases started with the biosimilar somatropin. Subjects who started with the biosimilar switched more frequently to anoth-er product and the change was less likely preceded by a specialist visit.