Thalidomide was a widely used drug in the late 1950s and early
1960s for the treatment of nausea in pregnant women. It became
apparent in the 1960s that thalidomide treatment resulted in
severe birth defects in thousands of children. Though the use of
thalidomide was banned in most countries at that time,
thalidomide proved to be a useful treatment for leprosy and later,
multiple myeloma. In rural areas of the world that lack extensive
medical surveillance initiatives, thalidomide treatment of pregnant
women with leprosy has continued to cause malformations.
Research on thalidomide mechanisms of action is leading to
a better understanding of molecular targets. With an improved
understanding of these molecular targets, safer drugs may be
designed. The thalidomide tragedy marked a turning point in
toxicity testing, as it prompted United States and international
regulatory agencies to develop systematic toxicity testing protocols;
the use of thalidomide as a tool in developmental biology led
to important discoveries in the biochemical pathways of limb
development. In celebration of the Society of Toxicology’s 50th
Anniversary, which coincides with the 50th anniversary of the
withdrawal of thalidomide from the market, it is appropriate to
revisit the lessons learned from the thalidomide tragedy of the
1960s.
Key Words: birth defects; teratogen; multiple myeloma; leprosy;
testing.
Thalidomide was first marketed in the late 1950s as
a sedative and was used in the treatment of nausea in pregnant
women (Fig. 1). Within a few years of the widespread use of
thalidomide in Europe, Australia, and Japan, approximately
10,000 children were born with phocomelia, leading to the ban
of thalidomide in most countries in 1961. Some countries
continued to provide access to thalidomide for a couple of
years thereafter (Lenz, 1988). In addition to limb reduction
anomalies, other effects later attributed to thalidomide included
congenital heart disease, malformations of the inner and outer
ear, and ocular abnormalities (Miller and Stro¨mland, 1999).
The thalidomide tragedy was averted in the United States
because of the hold on its approval by Dr Frances Kelsey of the
U.S. Food and Drug Administration, who was recognized by
President John F. Kennedy as a recipient of the Gold Medal
Award for Distinguished Civilian Service. Dr Kelsey’s
decision to hold the approval of thalidomide was not because
of the birth defects, which had not yet been attributed to
thalidomide, but because of her concerns about peripheral
neuropathy (sometimes irreversible) in the patient and the
potential effects a biologically active drug could have after
treatment of pregnant women. The thalidomide tragedy also
brought into sharp focus the importance of rigorous and
relevant testing of pharmaceuticals prior to their introduction
into the marketplace (Kelsey, 1988). Dr Kelsey was awarded
an honorary membership to the Society of Toxicology in
celebration of its 50th Anniversary in 2011.
Josef Warkany, one of the founders of the Teratology
Society, doubted in April of 1962 that thalidomide was
responsible for the epidemic of limb defects (Warkany, 1988).
His reasoning was that rat experiments had not produced
comparable malformations and that malformations in humans
were inconsistent (i.e., some mothers who were exposed to
thalidomide had normal children and some malformations
occurred in children whose mothers did not knowingly take
thalidomide) (Warkany, 1988). The thalidomide episode led to
the adoption of requirements for the systematic testing of
pharmaceutical products for developmental toxicity prior to
marketing. The adoption of these requirements is sometimes
considered a benefit of the thalidomide tragedy. The legacy
of thalidomide extends further than the creation of detailed
testing protocols. With thalidomide came, the widespread
recognition that differences in sensitivity between species
required consideration. As a consequence, developmental
toxicity testing for pharmaceuticals is conducted in two