Drug exposure during breastfeeding: a descriptive population- based cohort study with SIDIAP database

Background There is a gap in the knowledge of drug exposure during breastfeeding due to exclusion of lactating individuals from studies. It makes difficult to fully understand the implication of drug use while breastfeeding and potential risks to newborns. Breastfeeding information in the Electronic Health Records (EHR) may help us to increase this evidence. We aimed to describe drug exposure during breastfeeding in mothers of a cohort of mother-infant linked pairs in Catalonia, Spain. Methods We conducted a descriptive population-based cohort study including mother-infant linked pairs of infants born during 2010–2022. The data source was the Information System for Research in Primary Care (SIDIAP), including sociodemographic characteristics, comorbidities, prescribed and reimbursed drugs, and lactation registers. Lactation is registered in the infants’ EHR. We analyzed drug exposure from delivery up to 2, 4, 6 and 12 months afterwards. We described categorical variables by absolute frequency and percentage and continuous variables by mean and standard deviation. Results We included 176,324 mother-infant pairs with lactation registers during the first year after birth. Breastfed infants decreased during the first year to 64,225 (36.4%). Drug exposure varied from 76,064 (43.1% of the lactating mothers) from delivery up to month 2, to 32,475 (21.9%), 17,396 (17.6%) and 20,433 (31.8%) at up to months 4, 6 and 12, respectively. The most dispensed drugs were iron (25%), folic acid (15.5%) and analgesics (17.8%). Paracetamol was the most frequent analgesic (89.7%), amoxicillin and fosfomycin were the most frequent antibiotics (92.4% and 89.4%), or ibuprofen the most frequent non-steroidal anti-inflammatory drug (75.6%). Conclusions The number of lactating and drug-exposed mothers decreased over time. Iron and supplements were the most used drugs, mainly during the first two months, probably due to continuation since pregnancy or post-partum anemia. Analgesics and penicillins were also frequent, which might be used for common acute conditions. Our main limitation is the potential underreporting of drug exposure due to lack of information on over-the-counter drugs. Trial registration “Drug use in pregnant and breastfeeding women. Outcomes in the health of the women and the offspring”, EUPAS47450, registered at the HMA-EMA Catalogues of real-world data sources and studies: https://catalogues.ema.europa.eu/node/3222/administrative-details