L-T 4 Bioequivalence: Potential Impact on IQ in Babies with Congenital Hypothyroidism Rosalind Brown MD, Children’s Hospital, Boston Harvard Medical School

Congenital Hypothyroidism Because newborns are asymptomatic at birth, screening programs developed worldwide Incidence 1 in 3,000 treatableOne of the commonest treatable causes of mental retardation

Untreated CH Patients at Risk for Severe Mental Retardation Klein et al, J Pediatr 81: , 1972

IQ of CH patients is normal if treatment early and adequate NECHC. Lancet 2: , 1981

But small differences in T4 dose have enormous impact on IQ MDI- Mental Development Index T4 dose Bongers-Shokking JJ et al, J Pediatr 136: ,2000 *

Conclusions Small differences in L-T4 dose can have significant, irreversible consequences on IQ A potential difference of 33% in drug content therefore unacceptable T4 bioequivalence should be determined by the most sensitive means possible, that is by measurement of TSH