Objective: Indices are a common statistical measure to assess and compare prices of pharmaceuticals. They provide a rough estimate about the price level of a country in comparison to other countries. However, the aggregation of individual prices to one statistical metric is linked to methodological challenges. The most relevant topics are (1) matching of products in an off-patent market, as products are not available in all countries, and (2) adjusting for outliers that have no relevance in prescribing. The aim of this study is to compare the use of unweighted and weighted prices during index construction for adalimumab 40 mg.
Methods: Data on medicines containing adalimumab 40 mg was collected for twelve European countries through the EURIPID database. Unit prices and prescribed volumes for 2023 have been collected for the originator of adalimumab, and seven biosimilars. National currency units were converted by using fix exchange rates. A Laspeyres index was calculated for Austria by using (1) unweighted average of prices or (2) weighted average price which considered differing relevance of adalimumab products in each country.
Results: Using the unweighted average of prices, only Latvia has lower prices for adalimumab than Austria. On the other end of the ranking, prices in Norway and Czech Republic are more than the double than Austrian prices. When switching to weighted average of prices, the order of countries - especially at each end - changes: Swedish prices are almost the half of Austrian prices, whereas the prices in Estonia are triple.
Conclusions: The use of the weighted average price to construct the Laspeyres address both initial stated problems. In comparison to indices with unweighted average prices the difference in relative prices levels changes significantly. Like the ‘Big Mac’ index this adalimumab index provides a quick overview of price levels for biological medicines in a competitive market.