Prescription drug utilization in pregnancy : a systematic review and population-based study in British Columbia, Canada

Background – There is little evidence on the patterns of prescription drug use during pregnancy in Canada. To address this knowledge gap, the primary objectives of this thesis were to: 1) systematically review published antenatal drug utilization studies, and 2) provide the first Canadian evidence on prescription drug utilization across the pregnancy period, overall, by therapeutic category and fetal risk classification, in the province of British Columbia (BC). Methods - This thesis is comprised of two original studies. The first, a systematic review of antenatal drug utilization studies, was conducted according to an a priori protocol and included a double independent review process for the selection of articles and data abstraction. The second, a population-based empirical study in BC, was based on pharmacy claims records linked to maternal hospital records. The period of pregnancy was constructed from the recorded gestational age and prescriptions filled before, during, and after this period were analyzed. Drugs were classified according to the World Health Organization Anatomical Therapeutic Classification System and US Food and Drug Administration risk categories indicating potential for fetal harm (categories D and X). Results – Published drug utilization studies reveal wide variation in estimates of overall prescription drug use in pregnancy (27% to 93% excluding vitamins and minerals). However, estimates are difficult to compare due to differences in methodology, data sources, classification of prescription medicines, and inadequate reporting. In BC, the majority of pregnant women (63%) filled at least one prescription in pregnancy and approximately 1 in 12 filled a prescription for a drug with potential risks (category D or X). The most commonly used medicines were antiinfectives, doxylamine, dermatologicals, and drugs acting on the nervous system. Conclusion - A methodological framework and template for reporting exposures in pregnancy should be developed to improve the quality and comparability of antenatal drug utilization studies. Evaluation of medicines with unknown risks that are commonly used in pregnancy should be a priority for pharmacoepidemiological research. The use of drugs with potential risks should be targeted by programs to improve appropriate prescribing in pregnancy.Medicine, Faculty ofPopulation and Public Health (SPPH), School ofGraduat