Sarah Delaney (Presenter)
SickKids Hospital/University of Toronto
Authorship: Sarah Delaney (1), Masanobu Takeuchi (2), Ernest Wong (3), Cristiana Stefan (3), Shinya Ito (1, 2), David Colantonio (1, 2)
(1) University of Toronto, Toronto, ON Canada, (2) SickKids Hospital, Toronto, ON, Canada, (3) Centre for Addiction and Mental Health, Toronto, ON, Canada
| Short Abstract The health benefits of breastfeeding are well described. It has been reported that ~70% of women take medication in the postpartum period; however, little is known about drug excretion into breast milk. Measuring drug concentrations in breast milk will help determine the extent of infant drug exposure and risk for toxicity. We developed two LC-MS/MS assays to measure concentrations of two first line medications, escitalopram and methotrexate, in milk. An animal model, population pharmacokinetics, and physiologically-based pharmacokinetic modeling were used to help provide insight into the risk of infant drug exposure via breast milk. |
Long Abstract
Introduction: The health benefits of breastfeeding are well known for both infant and mother. Current American Academy of Pediatrics guidelines recommend exclusive breastfeeding for at least the first 6 months of life. It has been reported that 66-80% of women take medication in the postpartum period; however, data on drug excretion into milk is limited and the risk of drug exposure to the nursing infant largely remains unknown. The lack of knowledge and uncertainty on drug safety during lactation causes women to discontinue breastfeeding prematurely or decide not to initiate breastfeeding altogether. Further complicating this issue, there have been reports of infant adverse events and even fatalities in infants exposed to drugs in breast milk. Chronic diseases such as postpartum depression and rheumatoid arthritis (RA) are common diseases occurring in the postpartum period and often require the use of medication for disease control. Escitalopram (ESC) and methotrexate (MTX) are considered to be first line treatments for postpartum depression and rheumatoid arthritis, respectively; however their safety during lactation is limited. Although not all drugs may be considered incompatible with breastfeeding, it is essential to determine safety profiles of drugs commonly used during the lactation. The objectives of this study are to: 1) develop LC-MS/MS methods with additional sensitivity to measure low concentrations of ESC and MTX in breast milk, 2) using a mouse model, determine the role of drug transporting proteins in excreting drugs into milk, and 3) perform population pharmacokinetics (popPK) and physiologically-based pharmacokinetic modeling (PBPK) to simulate drug concentrations in milk and infant plasma to estimate risk of toxicity.
Methods: Women receiving ESC or MTX therapy were recruited through the SickKids hospital pregnancy and lactation helpline as part of the Drugs in Lactation Analysis Consotrium (DLAC) study framework. Breast milk was collected at 3-5 time points across their dosing interval. Breast milk is a complex lipid- and protein- rich matrix, with drugs partitioning to either the aqueous or lipid phase, thus requiring meticulous sample processing before analysis. The difference in composition between foremilk and hindmilk must also be considered, as hindmilk is more lipid-rich than foremilk. We experimented with various organic solvents to create a simplified drug extraction method using hexane, methanol and acetonitrile to facilitate efficient drug extraction from breast milk. Two LC-MS/MS methods were developed for ESC/desmethylescitalopram (D-ESC) and MTX/7-hydroxymethotrexate (7OH-MTX). The Thermo Scientific™ TSQ™ and Ab Sciex™ QTRAP® 5500, were the platforms used to measure ESC/D-ESC and MTX/7OH-MTX, respectively. Both methods utilized multiple reaction monitoring (MRM) using electrospray ionization in positive mode. The methods were both validated in accordance with CLSI guidelines in terms of linearity, precision, recovery, limits of quantification, ion suppression and method comparison.
It has been established that the Breast Cancer Resistance Protein (Bcrp) is up-regulated in lactating mammary epithelial cells. MTX is also a known substrate for Bcrp. To determine the involvement of Bcrp in excreting MTX into milk, wild-type (FVB) and Bcrp knockout mouse models were used. Mouse milk and plasma and human milk were collected and measured using the aforementioned LC-MS/MS method for MTX quantitation. Human milk was measured from 18 women taking ESC and popPK modeling was performed using the non-linear mixed effects program, NONMEM®, using the stochastic approximation expectation maximization using the ADVAN5 subroutine. PBPK modeling was performed to simulate infant plasma drug concentration from breast milk ESC exposure using PK-SIM® software.
Results: Results from the development and validation of both the ESC/D-ESC and MTX/7OH-MTX methods will be presented.
Animal Model- Bcrp knockout mice and mice treated with a chemical Bcrp inhibitor had significantly higher plasma concentrations and lower milk concentrations of MTX compared to wild-type. These results suggest that Bcrp is a major elimination pathway for MTX and also in plays a role in mediating transport of MTX into milk.
MTX- Pharmacokinetic profiling of MTX/7OH-MTX in human milk were determined following a weekly subcutaneous dose of 25 mg. Peak MTX/7OH-MTX milk concentrations were <4 nmol/L and occurred between 1-24 hours post dose; the concentration steadily decreased between 12-48 hours, with small but detectable levels from 48-96 hours. There were no difference in concentrations between the foremilk and hindmilk for MTX, however there was no detectable 7OH-MTX in the hindmilk.
ESC- There was no significant difference between ESC concentrations in the foremilk and hindmilk. A one-compartment model (+ absorption) with a proportional residual error model was selected to best describe the time-concentration profile of ESC in milk. Based on this final popPK model, we were able to estimate the infant’s exposure to ESC in milk by simulating milk concentrations in 1000 women. The median dosage an infant would be exposed to via milk was 0.009 mg/kg/day. The infant dose at the 99th percentile was 8.8% of the weight-adjusted maternal daily dose, which was approximately 0.018 mg/kg/day. Based on this data, infant ESC exposure via breast milk is well below the Reference Dose, which is considered that maximum daily oral dose that should not cause any adverse events. PBPK-simulated infant plasma ESC concentrations from breast milk ingestion will be presented.
Conclusions: Our data suggests that Bcrp is involved in transporting MTX into milk. However, MTX excretion was not completely eliminated in the Bcrp knockout mice, implying alternate drug transporting pathways are also involved. The concentration of MTX excreted into breast milk following low-dose MTX therapy is minimal and may not pose a risk to the nursing infant. More data is required to perform pharmacokinetic modeling on MTX in breast milk. This data also suggests that infant exposure of ESC in breast milk is less than 10% of the maternal weight-adjusted dose, suggesting the risk for infant adverse events may be low. Therapeutic drug monitoring, mechanistic drug transporter and pharmacokinetic modeling/simulation data from this study provide a comprehensive view of drug excretion into milk that will help guide decision making for drug use during lactation. Filling in the gaps of knowledge that exist in this area is essential to understanding drug safety and preventing the risk of adverse events in infants exposed to drugs through breast milk.
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