But local and international Aids activists praised the move, saying it would improve access to a key HIV drug.

Merck Sharp and Dohm (Thailand), a branch of pharmaceutical giant Merck that owns Efavirenz, said while it recognised the Thai government's legal right to break the patent, "compulsory licensing should be the last choice".

Merck had planned to meet with the government to find an appropriate solution. The statement was issued after the ministry said on Wednesday compulsory licensing would take effect immediately to allow access to the live-saving drug at a lower price.

Thawat Suntrajarn, director general of the Department of Disease Control said: "After a discussion with the Council of State, we agreed that the patent with Merck provided us a chance to import the drug from other sources. The company has been informally informed about the decision and they have a chance to legally challenge us.

"We need to break the patent because the price is too high for the government to afford, as new Aids patients increase every year by tens of thousands," he said.

Medecins San Frontieres (MSF) praised the decision, saying it would improve access to a key HIV/Aids drug.

"Efavirenz is currently patent-protected in Thailand, and the resulting monopolistic situation is limiting supply and affordability," said David Wilson, MSF's medical co-ordinator in Thailand.

"The patent holder, Merck, has on several occasions been unable to supply Efavirenz. This has resulted in treatment interruptions, forcing several hospitals to supply sub-optimal dual therapy," he said.

The Nation, AFP