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Treats and prevents erythema nodosum leprosum, a skin disease caused by leprosy. Used in combination with dexamethasone to treat multiple myeloma.
Chemists can produce organic compounds in huge numbers. Tested in animals, most either have no effect at all, or are so toxic that they cannot be considered as drugs. At least two different groups of animals are used. Usually small rodents - like rats, mice or guinea pigs - are tested first, then larger animals like dogs or monkeys.
More refined tests with smaller doses are carried out on young animals, to make sure that the drug does not prevent growth, and on pregnant animals to check that the drug does not harm their young. Other animals are watched for rashes, or unusually active or inactive behaviour.
Despite all these tests the results may still be misleading. Drugs do not always affect animals in the same way as humans. Penicillin, which has saved millions of human lives, might never have been marketed if it had first been tested on guinea pigs, because a very small dose will kill them. Toxicity testing is highly complex and can often take more than two years to complete.
The next stage is to test drugs for side effects in healthy human volunteers. Very small doses are given in strictly controlled circumstances. If the drug appears to have no harmful side effects the volunteer group is expanded. In America between 5000 and 15,000 people are usually monitored before the results of the tests are sent to the licensing authority (the US Food and Drug Administration).
The drug company reports all its findings in a document that often runs to many thousands of pages. If the report is approved, the drug undergoes clinical trials on patients to see how effective it is.
Most new drugs are 'double blind' tested. Half the patients are given an identical-looking placebo (something that has no effect). Neither doctors nor patients know which patient is given which.
The results of the tests must be sufficiently convincing for the drug to pass the clinical trials. There must be no doubt that it was the drug that relieved the patients' illnesses - not their own natural resistance. During all tests, doctors continue to search for any side effects that were not picked up in earlier tests.