(SLC-024) Frequent drug exposure during breastfeeding: a 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 clinical trials and studies during this period. The lack of comprehensive data makes it challenging to fully understand the implication of drug use while breastfeeding and potential risks to newborns.

Objectives: Our objective was to describe drug exposure in mothers during breastfeeding.

Methods: Population-based cohort study including lactating mothers whose electronic health records were linked to their children born during January 2013-June 2023. We described the characteristics of the mothers and analyzed their drug exposure at months 2, 4, and 6 after birth. Drugs used by at least 2% of mothers in any of the time-cuts are described.
Data source: Information System for Research in Primary Care (SIDIAP), including pseudonymized clinical information of 5.8 million people from Catalonia, Spain: sociodemographic characteristics, comorbidities, clinical parameters, prescribed and reimbursed drugs. Lactation is registered in the children’s records.
Statistical analysis: We described categorical variables by absolute frequency and percentage and continuous variables by mean and standard deviation.

Results: We identified 176,324 mothers linked to their newborns who were breastfeeding 2 months after birth. At months 4 and 6, 148,413 (84.2%) and 98,635 (55.9%) respectively continued breastfeeding. Their mean age was 32.3 years, and their most frequent comorbidities were psychiatric diagnoses (24.9%), obesity (9.4%), neoplasms (5.8%), migraine (5.8%) and respiratory disorders (5%).
At month 2, 76,064 (43.1%) lactating mothers were exposed to drugs, being iron (23.2%), folic acid (14.7%), and vitamin B12 (12%) the most frequent ones. At month 4, 32,475 (21.9%) lactating mothers were exposed, being iron (5%), analgesics (4.4%) and folic acid (4.3%) the most used. At month 6, 17,396 (17.6%) were exposed and analgesics (4%), penicillins (3.5%) and non-steroidal anti-inflammatory drugs (3.1%) were the most used.
The most used substances overall were ferrous sulfate (17.8%), paracetamol (15.9%), folic acid (15.5%), amoxicillin (13.0%), cyanocobalamin (12.8%) and ibuprofen (10.3%).

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 after birth, probably due to continuation since pregnancy or due to post-partum anemia. Analgesics and penicillins were also frequent during breastfeeding, which might be used for common acute conditions, such as mastitis. Our main limitation is the potential underreporting of drug exposure due to lack of information on over-the-counter drugs.