ASTRAZENECA’S Japanese subsidiary is facing the threat of a class action lawsuit over the fatal side-effects of Iressa, its lung cancer treatment.

The 29 Japanese lawyers representing the families of Iressa victims are also mulling cases against the London-based parent company and are planning a fact-finding trip to the UK.

Documents presented to the Tokyo District Court also accuse AstraZeneca of a cover-up over the dangers of Iressa. Lawyers for Akio Chikazawa, whose 31-year-old daughter died from Iressa side-effects, accused the British pharmaceutical company of exploiting a loophole in the Japanese system and treating Japanese patients as “laboratory animals”.

As The Times revealed last month, Iressa’s side-effects have killed 588 people since the summer of 2002 when it was launched in Japan. AstraZeneca is already fighting Iressa compensation suits in Tokyo and Osaka, and faces a possible ban on the drug by the Japanese Ministry of Health and Welfare.

AstraZeneca said last night that it had complied with all international safety monitoring standards, and would vigorously defend the lawsuits. A spokeswoman said the benefits of Iressa outweighed the risk of adverse side-effects. Although fatal side-effects had been observed in patients who had received Iressa, it had not been possible to determine “whether a causal relationship exists”.

Revelations over the extent of Iressa side-effects have stunned Japanese authorities, who have set up an inquiry into the matter. Japanese lawyers claim that more than a third of those who suffered side-effects have died as a result. Japan makes up more than 40 per cent of Iressa’s global sales.

The Iressa Victims’ Association is fighting for a ban on Iressa, which they say exploited their desperation by specifically promising them the “drug of their dreams”.

The first hearing in Mr Chikazawa’s civil case will take place next week, and his lawyers are expected to focus first on the “murky” process by which Iressa was granted approval by authorities in Japan — a process that took half the normal time.

AstraZeneca dropped approval applications in the EU after the drug was shown in trials to have virtually no effect on Caucasians, but pushed for a launch in Japan when it showed mild benefits for Asian cancer patients.

Japan does not require Phase III trials for cancer drugs before they come to market and was the first country to approve sales of Iressa. Lawyers in the Tokyo case against AstraZeneca allege that the British company exploited this fact to test the drug on Asians, who, like Mr Chikazawa’s daughter, would take the treatment as a drug of last resort.

Lawyers in the Tokyo case accuse the Japanese Ministry of Health of being “slapdash” in its approach to the drug, but reserve their main body of criticism for AstraZeneca.

Yesterday, shares in AstraZeneca jumped 2.2 per cent to £20.70 after the company said on Tuesday that it did not expect advisers to the US Food and Drug Administration to vote next month on whether Iressa should be pulled from the market.