LONDON, Dec 1 (Reuters) - U.S. drugmaker AbbVie has added two HIV medicines for children to a shared patent pool in an initiative that should speed the development of cheap new paediatric formulations for use in poor countries.

It is the latest win for the non-profit Medicines Patent Pool (MPP), which aims to persuade leading drug companies to share rights to their products with generic manufacturers in India and elsewhere.

Until now, AbbVie has not participated in the scheme, although the MPP has signed HIV drug agreements with Bristol-Myers Squibb, Gilead Sciences, Roche and ViiV Healthcare, which is majority-owned by GlaxoSmithKline.

Despite major advances in treating HIV/AIDS, only a quarter of the 3.2 million children with the virus - 90 percent of whom live in sub-Saharan Africa - currently receive drugs.

One major obstacle is the fact that existing syrup-based formulations need refrigeration, making them unsuitable for much of Africa, and their unpleasant taste is an added problem.

The licensing agreement for AbbVie's lopinavir and ritonavir drugs, both of which are specifically recommended for children, gives a green light to other players to develop improved treatment options.

The licence also allows for the development of fixed-dose combinations using different drugs already covered by MPP deals with other companies.

The MPP-AbbVie agreement covers 102 countries and also permits distribution in areas where AbbVie does not hold patents, such as in India where the company has withdrawn its patent applications for lopinavir and ritonavir.

(Reporting by Ben Hirschler, editing by David Evans)