A court in Thailand has removed the exclusive right of pharmaceutical company Bristol-Myers Squibb (BMS) to manufacture the antiretroviral didanosine (ddI) by ruling that its patent only covered tablets containing 5-100 mg of didanosine. The Central Intellectual Property and International Trade Court gave the company one month to appeal.

The ruling has paved the way for others to manufacture cost-effective didanosine tablets with dosages of more than 100 mg of ddI, Paul Cawthorne of Medecins Sans Frontiere's Thailand office told The Lancet. "We are ready to manufacture ddI tablets of 125 150, and 200 mg dosages.

A 125 mg tablet will be priced at about 45 cents", said Krisana Kraisintu from the state-run drug manufacturer, Government Pharmaceutical Organization, which intends to seek the court's approval this month to begin producing the tablets during the period set aside for the appeal, which could take months or years to be decided. BMS sells its ddI tablet at about 92 cents per tablet, which is too expensive for the Thai government to buy for its one million HIV infected people. In the original application, BMS limited its ddI patent to 5-100 mg per unit but several years later it asked the Thai Department of Intellectual Property (DIP) to amend its application.

The amendment did not specify the amount of ddI per tablet and the department approved the application, a decision that strengthened BMS's ddI manufacturing rights. Angered by the revision, last year the Aids Access Foundation, a non-governmental organisation, sued BMS and the DIP. On Oct 1, the court called the amendment "unlawful" and asked BMS and the DIP to restore the original limits to formulation in the patent.

Cawthorne said "such lack of transparency in the issuing and amending of patents may not be limited to Thailand". Meanwhile on Oct 9 the Thai Foundation for Consumer filed a suit that challenges the right of BMS to even hold a patent on didanosine. The plaintiffs argue that the patent should never have been issued because the addition of a buffer to the active ingredient lacks sufficient inventiveness to warrant a patent.

Cawthorne argued that many pharmaceutical patents are issued with little regard to the degree of inventiveness in the process and that companies exploit this weakness in international patent law to maintain market exclusivity. "Should the court rule in favour of the plaintiffs and revoke the patent ... the implications will be far reaching as the Thai patent is based on a patent issued in Australia.

Patents held by BMS in the USA and the European Union also use the same basis to establish inventiveness. Therefore all these patents would be put into question", Cawthorne pointed out.