High levodopa use in periodically time-clustered, Icelandic birth cohorts. A vestige of parkinsonism etiology? Europarkinson Preparatory Activity Research Group.

We evaluated levodopa use (LDU) by the Icelandic population focusing on: 1) annual gross levodopa (LD) sales from wholesalers to pharmacies for the period 1978-1990, using a reported method; 2) data from a prescription survey conducted from October 1st, 1990 to March 31st, 1991; and 3)raw and reported data on prevalences of Parkinson's disease (PD) in 1963 in this country. The standard for adjustments and reference population for LDU comparisons was the Swedish in 1984. Crude gross sales of LD in Iceland in 1990 and in Sweden in 1984 amounted to 1.67 and 1.35 DDD/1000 person days respectively. After respective adjustments for age, and for age and the infant mortality rates, taken as an indicator of health care quality, LDU in Iceland in 1990 was found to be 1.82 and 1.63 (95% CI 1.47-1.89) times that for Sweden. Prevalences of LD-prescription recipients in 1990-1991 and of PD in 1963 increased with age; however, those of drug users were higher than those of PD among the elderly. Higher-than-expected prevalences of PD and LD-prescription users (there being a partial overlap between these two categories) were found in periodically-clustered, one-year birth cohorts. These results support the notion that Iceland has a high LDU and suggest that this variation is due to a high prevalence of LD responsive disorders. Cohorts born after registered whooping cough outbreaks in Iceland may account for the magnitude and birth-related pattern of PD prevalences and LDU levels.