AstraZeneca K.K., the Osaka-based importer of the controversial cancer drug Iressa, may have failed to notify health authorities of the drug’s acute side effects within the time period set by the government, sources said Friday.

The Health, Labor and Welfare Ministry has launched an investigation to determine whether AstraZeneca violated the Pharmaceutical Affairs Law. If found in breach of the law, the firm may face disciplinary action, including an order to halt operations.

Iressa, known by its generic name gefitinib, has been administered to about 23,000 patients so far, 183 of whom have died after suffering from side effects.

Under the Pharmaceutical Affairs Law, pharmaceutical companies must notify the health ministry within 15 days when doctors report previously unknown side effects. The ministry must be notified within 30 days if the side effects are listed by the manufacturer on the prescription.

The law also stipulates, however, that pharmaceutical companies must give notice within 15 days if the known side effects are found to be occurring at a rate higher than predicted in clinical data.

AstraZeneca received information on 45 cases of acute side effects between late last August, when the drug was approved for insurance coverage, and Oct. 11, shortly before the ministry ordered the company to issue an emergency safety warning amid rising reports of acute side effects.

Of the 45 cases, the ministry was notified of about 40 of them within 30 days but after the 15-day limit for unlisted side effects, the sources said.

AstraZeneca said it thought it was appropriate to notify the ministry within 30 days, as the reported side effects had been described in the side effect warning that comes with the drug.

After an in-house investigation, the company later found a document showing that by Sept. 11, AstraZeneca officials were already aware that interstitial pneumonia, one of the side effects associated with the drug, was occurring at a higher rate than indicated in clinical data.

The internal document indicated that AstraZeneca knew interstitial pneumonia was hitting 1 percent of the patients who took the drug. Clinical tests conducted by AstraZeneca put the occurrence rate at between 0.2 percent and 0.4 percent.

The health ministry suspects AstraZeneca failed to act promptly even though it was aware that interstitial pneumonia was occurring at a higher rate.

“We plan to conduct a thorough investigation to determine the facts,” said Tatsuo Kurokawa, head of the health ministry’s safety department.

Kurokawa said the ministry will take “strict measures” if AstraZeneca is found to have violated the law.

The controversial drug was developed by AstraZeneca PLC of Britain to treat lung cancer.

Since Japan approved the drug last July ahead of the rest of the world, doctors across the country reported a series of acute side effects, primarily interstitial pneumonia.

The health ministry issued an emergency warning in late December that included compulsory hospitalization during the first four weeks of administration of the drug and declared that only doctors with expertise in treating lung cancer with drugs could administer the drug.

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