Xaluprine is manufactured by UK-based Nova Laboratories, which is set to issue updated packaging through distributor Trimedica to its European customers.
The extension is expected to reduce wastage, particularly for young children.
Nova clinical development head Hussain Mulla said the news was a positive step in the treatment of ALL across Europe.
"Many pharmacists acknowledge the superior benefits of prescribing mercaptopurine in liquid form, as opposed to tablets, in terms of palatability, dosing accuracy and safety, but face downward pressure on costs," Mulla added.
"The EMA ruling means that for younger patients the product is now effectively half its original cost, which we hope will encourage pharmacists to consider it as a more viable option."
Xaluprine is available throughout Europe, including the UK and Ireland, the Netherlands, Germany and Scandinavia.