THALIDOMIDE

compound in medicine initially used as a sedative and an antiemetic until the discovery that it caused severe fetal malformations. Thalidomide was developed in West Germany in the mid-1950s and was found to induce drowsiness and sleep. The drug appeared to be unusually safe, with few side effects and little or no toxicity even at high doses. Further testing revealed that thalidomide was particularly well-suited to alleviating nausea and other symptoms associated with morning sickness in pregnant women. The drug's potentially harmful effects on the fetuses of certain mammals was not recognized during testing. Thalidomide went on the market as a treatment for morning sickness in more than 40 countries beginning in 1958. It was soon found to produce severe malformations in infants born of mothers who had taken the drug during early pregnancy. These included phocomelia (seal limbs, in which the long bones in the arms and legs fail to develop) and other deformities such as absence or malformation of the external ear, fusion defects of the eye, and absence of the normal openings of the gastrointestinal tract. Fetuses are vulnerable to the drug's effects only during the period from 27 to 40 days after conception, but the drug nonetheless caused deformities in an estimated 5,000 to 10,000 infants. Once these effects became known, thalidomide was taken off the market in 196162. In the United States, the Food and Drug Administration (FDA) had been slow to approve thalidomide, so it was never distributed for clinical use there. Teratogens (agents that cause birth defects) are still not fully understood. In the late 1950s physicians and pharmacologists little suspected that drugs that were nontoxic to an adult could cause deformations in a fetus. The issue was also complicated by the fact that thalidomide is harmful only during certain specific times in human fetal development. Though it achieved worldwide notoriety as a cause of birth defects and was withdrawn from use as a sedative, thalidomide eventually proved to have therapeutic uses. In the mid-1960s clinicians discovered that it can effectively treat the painful skin nodules and nerve impairment caused by erythema nodosum leprosum (ENL), a complication of leprosy. Thalidomide achieves this therapeutic effect by limiting the immune system's powerfuland harmfulinflammatory response to leprosy bacilli within the body. Further testing revealed that thalidomide also has a significant anti-inflammatory effect in the treatment of rheumatoid arthritis and other autoimmune diseases. Thalidomide derives this effect from its ability to inhibit the body's production of tumour necrosis factor (TNF), a protein that is a powerful stimulator of inflammation within the body. In the 1990s thalidomide was found to be effective in treating cachexia, the severe weight loss that occurs in patients with diseases such as AIDS, tuberculosis, and leprosy. Cachexia is apparently caused by the body's overproduction of TNF. In 1998 the FDA approved the use of thalidomide in the treatment of ENL, although distribution was to be closely regulated because of the drug's dangerous teratogenic properties. In AIDS patients, in addition to treating cachexia, thalidomide was also useful in treating lesions of the mouth and throat, and early tests indicated that the drug may inhibit the replication of the AIDS virus.