LONDON (Reuters) – International medical charity Médecins Sans Frontières (MSF) on Monday accused specialist HIV drugmaker ViiV Healthcare of delaying access for children with the AIDS virus to a critical medicine called dolutegravir.

While the World Health Organization (WHO) recommends dolutegravir as a preferred treatment for children four weeks to 10 years old and adults, ViiV has failed to register and make available pediatric formulations in many countries where it is most needed, MSF said in statement.

The group, known as Doctors Without Borders in English, also said ViiV was making pediatric formulations more expensive than adult versions, and was slow to develop dispersible versions for babies.

ViiV is a joint venture between the U.S. pharmaceutical giant Pfizer Inc, Britain’s GlaxoSmithKline Plc and Japan’s Shionogi & Co Ltd .

“These barriers force HIV-positive children to rely on pediatric treatments containing suboptimal drugs with more side effects,” MSF said. “ViiV is dragging its feet when it comes to getting better treatment to children with HIV.”

The medical charity also said ViiV’s pricing structure for dolutegravir was “problematic,” with an adult 50 milligram (mg) dose costing around $223 per year, compared with child formulation dose costs of $214 for 25mg and $115 for 10mg.

Dolutegravir belongs to a class of drugs known as integrase inhibitors and is used in ViiV’s branded combination HIV drugs Tivicay and Triumeq. Gilead Sciences Inc makes a rival product called bictegravir.

ViiV responded in a statement that it was “focusing efforts on accelerating the development and availability” of dolutegravir and its other HIV drugs to all age-groups.

The drugmaker said prices for dolutegravir formulations are not fixed, but based on the “cost of manufacture plus distribution” for poorer countries until cheaper generic formulations become available.

MSF said ViiV had failed so far to deliver on pledges to speed up availability of pediatric dolutegravir formulations where they are most needed, including in sub-Saharan Africa where the majority of HIV positive patients live.

“ViiV needs to recognize its responsibility as today’s only producer of pediatric versions of the new gold standard in treatment for babies and children with HIV, and move mountains to make sure kids can access this treatment immediately,” said Jessica Burry, an HIV pharmacist with MSF.

(Reporting by Kate Kelland; Editing by Richard Chang)