U.S. healthcare group J&J said on Thursday it would not enforce patents, provided generic firms made high-quality versions of the drug - known generically as darunavir - for sub-Saharan Africa and Least Developed Countries.

Prezista is a relatively new drug used when patients develop resistance to older antiretrovirals. The need for it was expected to grow rapidly as more patients in Africa stop responding to existing therapies.

Pharmaceuticals head Paul Stoffels said he expected Indian drugmakers, in particular, to take advantage of the patent move, adding that competition among different companies should drive prices down further.

J&J has an existing deal with South African group Aspen Pharmacare, which makes Prezista at a discounted price of $2.22 per day for Africa - a fraction of the western market price.

Its decision to act unilaterally on Prezista patents will, however, disappoint those calling for J&J to share intellectual property rights in the new Medicines Patent Pool, which aims to streamline generic production by pooling patents.

"We have chosen to go direct ... we think that is the best way," Stoffels said in an interview.

"We want to reserve the right to reinforce patents if people are not providing the right quality of product, for example by bringing products to market that under-dose."

International drugmakers are under growing pressure to make medicines more affordable in poor countries, after being attacked for not doing enough in the past.

J&J ranked second in a new analysis of how companies are performing in providing access to medicines - an improvement of seven places from two years earlier, following its purchase of Crucell, which makes vaccines for the developing world.

(Editing by Dan Lalor)

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