Pharmacokinetics of Ketamine Transfer Into Human Milk.

PURPOSE/BACKGROUND: Ketamine is an N -methyl- d -aspartate-antagonistic dissociative anesthetic infused intermittently for off-label management of treatment-resistant depression, acute suicidality, and postpartum depression. Despite the prevalence of postpartum depression nearing upward of 15% of deliveries, almost no research has been done to evaluate its safety during lactation. METHODS: In this study, human milk samples were released from the InfantRisk Center's Human Milk Biorepository of 4 participants treated with intermittent ketamine infusions (49-378 mg) to determine the levels of the drug and its active norketamine metabolite using liquid chromatography-mass spectrometry. RESULTS: The absolute infant dose of ketamine from human milk was 0.003 to 0.017 mg/kg per day, and norketamine was 0.005 to 0.018 mg/kg per day. The relative infant dose (RID) for ketamine ranged from 0.34% to 0.57%. The RID for norketamine ranged from 0.29% to 0.95%. There were no reported infant adverse effects. CONCLUSION: The findings of this study suggest that the transfer of ketamine, as well as its active metabolite, norketamine, into human milk is minimal, as estimated by RIDs less than 1% in all participants. These relative doses are well below standardly accepted safety thresholds.

Cladribine transfer into human milk: A case report.

BACKGROUND: Cladribine is an antimetabolite used for the treatment of relapsing-remitting multiple sclerosis. At present, there are no data available on its use in breastfeeding mothers and its transfer in human milk. OBJECTIVE: We present a case of a lactating mother who donated her milk samples to study the transfer of cladribine following a 20-mg oral dose. METHODS: Analysis was done using liquid chromatography-mass spectrometry. RESULTS: The relative infant dose calculated in this study was 3.06%. CONCLUSION: This is the first case report suggesting the transfer of cladribine in human milk in measurable quantities. However, caution should be advised during lactation.

Minimal to no transfer of certolizumab pegol into breast milk: results from CRADLE, a prospective, postmarketing, multicentre, pharmacokinetic study.

BACKGROUND: Women with chronic inflammatory diseases face uncertainty regarding the safety of biologics during breast feeding. CRADLE was the first industry-sponsored study to evaluate certolizumab pegol (CZP) concentrations in human breast milk and estimate average daily infant dose (ADID) of maternal CZP. METHODS: CRADLE (NCT02154425) was a pharmacokinetic study of lactating mothers receiving CZP. After ≥3 CZP doses, breast milk samples were collected across one dosing period (14 days for 200 mg every 2 weeks [Q2W]; 28 days for 400 mg every 4 weeks [Q4W]). Optimal analytical methods were developed to determine CZP and polyethylene glycol (PEG) levels in breast milk. ADID and relative infant dose (RID) were estimated. Safety events in mothers and infants were assessed. RESULTS: 19 CZP-treated mothers were screened; 17 entered the sampling period: 16 on 200 mg Q2W, 1 on 400 mg Q4W. 77/137 (56%) breast milk samples had no measurable CZP. For 4/17 mothers, all samples were below the lower limit of quantification (LLOQ). Estimated ADID was 0-0.0104 mg/kg/day; median RID: 0.15%. PEG was undetectable in 134/137 samples (results could not be determined in three samples). Infants of CZP-exposed mothers had a safety profile consistent with that of unexposed similar-age infants. CONCLUSION: When quantifiable, CZP concentrations were <3× LLOQ (<1% plasma concentration observed with therapeutic dose), indicating no/minimal CZP transfer from plasma to breast milk. RID was 0.15% of maternal dose; <10% is considered unlikely to be of clinical concern. No PEG transfer was observed. CZP absorption by infants via breast milk is unlikely due to its low oral bioavailability and Fc--free molecular structure. These findings are reassuring and support continuation of CZP treatment during breast feeding. TRIAL REGISTRATION NUMBER: NCT02154425; Results.

Drugs in Breast Milk.

Most drugs appear in breast milk in very small and safe amounts. The obstetric care provider evaluates drug transfer most commonly in the peripartum period, postpartum hospitalization; and they are often consulted when the new mother has a subsequent need for drug therapy. The chapter provides the foundations for the safest decisions for the mother and her breastfed infant. The foundation of safe decisions is accomplished through a review of the physiology of lactation, the lactation pharmacology, and the specific pharmacology and infant safety of drugs common to everyday obstetric practice.

Increasing earnings of social security disability income beneficiaries with serious mental disorder.

BACKGROUND: Persons with severe and persistent mental disorders (SPMD) have extremely low earnings levels and account for 29.1 percent of all U.S. Social Security Disability Income (SSDI) disabled worker beneficiaries under age 50. Social insurance and disability policy experts pointed to several factors that may contribute to this situation, including disincentives and obstacles in the SSDI program, as well as lack of access to evidence-based behavioral-health interventions. In response, the Social Security Administration (SSA) funded the Mental Health Treatment Study (MHTS) demonstration that included 2,238 beneficiaries of SSDI whose primary reason for disability is SPMD. The demonstration, implemented in 23 different localities, consisted of two evidence-based services (individual placement and support supported employment (IPS-SE), systematic medication management (SMM)), and provision or coverage of additional behavioral-health services (OBH). STUDY AIMS: This study focused on estimating MHTS intervention effects on earnings in the intervention period (two-years). The main outcome variable was self-reported average monthly earnings. METHODS: Subjects were randomly assigned to intervention or control groups. Data were drawn from the baseline survey, seven follow-up quarterly surveys, a final follow-up survey, and SSA administrative data. In all surveys, respondents were asked about earnings prior to the interview. Dependent variables were average past-30-days earnings reported in all follow-up surveys, similar averages for the first four follow-ups and for the last four follow-ups, fraction of surveys with prior earnings above SSA's substantial gainful activity (SGA) threshold, and final-follow-up earnings for the past 90 days. Regression analyses compared earnings of intervention vs. control group subjects. Covariates included baseline values of: (i) beneficiary demographic and social characteristics; (ii) beneficiary physical and mental health indicators; (iii) beneficiary recipiency history; (iv) beneficiary pre-recruitment and baseline earnings; and (v) local labor-market unemployment rates. RESULTS: Results show significant positive MHTS earnings impacts. Estimated annual increases of earnings range from USD791 (based on the 2-year average) to USD1,131 (based on the final quarter of Year 2). Effects on the fraction of quarters with earnings exceeding SGA are positive and significant but very small in magnitude. DISCUSSION: The consistent increase in earnings impacts over the study period suggests the possibility of even larger impacts with longer-term interventions. The moderate size of the intervention impacts may partly be explained by a study population that already had an average of 9 years on SSDI, and whose labor-supply decisions continued to be affected by concerns about possible loss of benefits. Limitations are that (i) earnings effects of specific intervention components cannot be estimated since all treatment subjects received the same package of services, and (ii) study results may not generalize to the majority of the beneficiary population due to selection effects in beneficiaries' participation decisions. IMPLICATIONS: Replication of the MHTS on a broader scale should show similar positive earnings impacts for a substantial number of beneficiaries with characteristics similar to the study population. Future studies should consider reducing policy barriers to labor supply of persons with SPMD. Future studies should consider longer-term interventions, or at least measuring impacts for follow-up periods greater than two years.

No Measurable Transfer of Oxytocin-Receptor Agonist Merotocin Detected in Human Breast Milk.

Objective: The study aimed to assess the transfer of merotocin from systemic circulation to breast milk in early postpartum women and women with established lactation. Methods: This was a two-part, multicenter, open-label, parallel-group study. Merotocin was administered as a single 90-minute intravenous (iv) infusion mimicking the intranasal pharmacokinetic profile. In Part A, 12 early postpartum women received doses of either 4 µg (n = 6) or 16 µg (n = 6) of merotocin within 4 days of delivery. In Part B, six women with established lactation received 20 µg of merotocin. The total concentration of merotocin in plasma and breast milk and its metabolites excreted in breast milk were measured at various time points. Adverse events (AEs) were also assessed for both parts of the study. Results: In both early postpartum and established lactation groups (mean age, 26.3 years; 83.3% Caucasian), merotocin and its metabolites in breast milk were below the limit of quantification (25.0 pg/mL) at all time points. Sixteen treatment-emergent AEs occurred in early postpartum women only, including seven events of uterine spasm and three of breast engorgement. There was one moderate event, whereas all the other events were considered mild. Conclusion: Merotocin was undetectable in breast milk after single iv administration of up to 20 µg in early postpartum women and women with established lactation.

Transfer of Injected Triamcinolone into Human Milk of a Lactating Patient Suffering from Idiopathic Granulomatous Mastitis.

Background: Idiopathic granulomatous mastitis (IGM) is a chronic inflammatory condition of the mammary gland that presents as a painful mass, and it must be distinguished from both infectious mastitis and breast cancer. When diagnosed during lactation, it can result in significant distress and early weaning. Injection of triamcinolone has been used as a successful treatment method, but safety in breastfed infants has not been established. Methods: We present a case of a lactating patient who received a direct injection of triamcinolone (dosage 40 mg) in her breast to treat IGM after failure of oral corticosteroids. Breastmilk samples were expressed by the patient 0, 1, 4, and 24 hours after the procedure, and then daily for 1 week. All the samples were analyzed using liquid chromatography mass spectrometry. The patient was supported by a breastfeeding and lactation medicine clinic. Results: After injection of triamcinolone into the granulomatous mass, breast milk samples were collected and analyzed. No samples were found to contain triamcinolone. A temporary but significant decrease in milk production was noted after injection, though only a slight decrease had been noted with 6 weeks of systemic corticosteroids. With support, the patient rebuilt milk production and continued to breastfeed from both breasts. Conclusion: Triamcinolone was not found in any milk samples (≥0.78 ng/mL) following therapeutic injection of the affected breast. The patient was able to continue breastfeeding from the affected breast with intermittent symptoms.

Anti-CD20 monoclonal antibody therapy in postpartum women with neurological conditions.

OBJECTIVE: Postpartum, patients with multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD) have increased risk for disease activity. Anti-CD20 IgG1 monoclonal antibodies (mAb) are increasingly used as disease-modifying therapies (DMTs). Patients may wish to both breastfeed and resume DMT postpartum. This study aimed to determine the transfer of anti-CD20 IgG1 mAbs, ocrelizumab, and rituximab (OCR/RTX), into mature breastmilk and describe maternal and infant outcomes. METHODS: Fifty-seven cis-women receiving OCR/RTX after 59 pregnancies and their infants were enrolled and followed up to 12M postpartum or 90 days post-infusion. Breastmilk was collected pre-infusion and serially up to 90 days and assayed for mAb concentration. Medical records and patients' questionnaire responses were obtained to assess neurologic, breastfeeding, and infant development outcomes. RESULTS: The median average concentration of mAb in breastmilk was low (OCR: 0.08 µg/mL, range 0.05-0.4; RTX: 0.03 µg/mL, range 0.005-0.3). Concentration peaked 1-7 days post-infusion in most (77%) and was nearly undetectable after 90 days. Median average relative infant dose was <1% (OCR: 0.1%, range 0.07-0.7; RTX: 0.04%, range 0.005-0.3). Forty-three participants continued to breastfeed post-infusion. At 8-12 months, the proportion of infants' growth between the 3rd and 97th World Health Organization percentiles did not differ for breastfed (36/40) and non-breastfed (14/16, p > 0.05) infants; neither did the proportion with normal development (breastfed: 37/41, non-breastfed: 11/13; p > 0.05). After postpartum infusion, two mothers experienced a clinical relapse. INTERPRETATION: These confirm minimal transfer of mAb into breastmilk. Anti-CD20 mAb therapy stabilizes MS activity before conception to the postpartum period, and postpartum treatments appears to be safe and well-tolerated for both mother and infant.

Psychiatric Manifestations of Withdrawal Following Domperidone Used as a Galactagogue.

Background: Domperidone is a dopamine-2 antagonist used off-label to increase breast milk production. Dosages commonly promoted for lactation are often far above those of studied on-label indications and might pose additional risks, especially upon discontinuation of the drug. Patients: Three U.S. patients are presented who used domperidone for lactation and experienced varying degrees of psychiatric withdrawal symptoms lasting months during dosage tapering and after cessation. Conclusion: Domperidone as a galactagogue may pose a significant psychiatric risk upon discontinuation. This presentation is commonly confused with, but clinically distinct from, postpartum depression. Lactating mothers who present with psychiatric symptoms should be explicitly probed about domperidone use, even in areas where domperidone is not authorized for use. Maternal hesitancy to disclose domperidone use may lead to suboptimal outcomes for the patient and delay management of withdrawal manifestations. The best course of treatment remains unknown, but a slow hyperbolic taper to gently discontinue domperidone may minimize withdrawal symptoms in these patients. Individuals exploring domperidone use should be informed of potential risks upon withdrawal, including psychiatric manifestations, requisite taper, and potential impacts of using unstudied high doses.

Mode of Cannabis Use and Factors Related to Frequency of Cannabis Use Among Breastfeeding Mothers: Results from an Online Survey.

Background: In the United States, 5% of breastfeeding mothers report using cannabis. Frequent cannabis use results in higher delta-9-tetrahydrocannabinol (THC) in breast milk, and mode of cannabis use may also impact risk to the infant. The aim of this study was to understand how breastfeeding mothers use cannabis and factors related to frequency of its use. Methods: An anonymous online survey was conducted among mothers who used cannabis while breastfeeding. Frequency of cannabis use was ascertained along with modes of and reasons for cannabis use. Respondents were grouped by frequency of use: less-than-daily (n = 686), low-daily (1-3 times/day; n = 423), and high-daily (≥4 times/day; n = 218). Chi-square and analysis of variance tested between-group differences, and ordinal logistic regression examined factors associated with cannabis use frequency. Results: Smoking (88%) was the most common mode of cannabis consumption, followed by vaping (48%) and oral/edibles (36%). Smoking and vaping differed by cannabis use frequency. Only 54% used cannabis to get high, but was reported more among frequent users. In contrast, 89% of mothers used cannabis for mental or physical health symptoms, including anxiety, depression, gastrointestinal symptoms, chronic pain, and posttraumatic stress disorder. These symptoms differed by cannabis use frequency. Reporting more symptoms was associated with higher frequency of use. The odds of increasing cannabis use frequency was 2.7 for those reporting 1-2 health reasons, 5.6 for those reporting 3-4 health reasons, and 13.1 for reporting ≥5 health reasons. Conclusions: Strategies are needed to address maternal mental and physical health, which may be key to reducing cannabis use among breastfeeding mothers.

Human Milk and Plasma Pharmacokinetics of Single-Dose Rimegepant 75 mg in Healthy Lactating Women.

Objective: Investigate whether rimegepant-an oral small molecule calcitonin gene-related peptide receptor antagonist for the treatment of migraine-is excreted in human milk after a single 75 mg dose and characterize its concentration-time profile in the plasma and milk of healthy lactating women to determine the relative infant dose (RID). Methods: This open-label, single-center study enrolled healthy lactating women aged 18-40 years with a gestation of 37-42 weeks and uncomplicated delivery of a single healthy child ≥2 weeks (14 days) and ≤6 months before study drug administration. Plasma samples were collected 0, 1, 2, 4, and 8 hours postdose; human milk samples were collected at 0, 1, 2, 4, 8, 12, 16, 24, 32, and 36 hours. The milk:plasma drug concentration ratio was estimated as the ratio of the human milk:plasma areas under the curve. The RID (%) was calculated as 100 times the quotient of the body weight-normalized infant and maternal doses. Results: Subjects (N = 12) were enrolled between 25 January and 15 September 2020. The mean (standard deviation [SD]) age was 29.8 (3.6) years; mean (SD) body mass index was 26.8 (4.9) kg/m2. The mean (SD) RID of rimegepant was 0.51% (0.14). The mean (SD) body-weight normalized infant dose was 0.005 (0.001) mg/kg/day, the mean (SD) body-weight normalized maternal dose was 1.04 (0.18) mg/kg/day, and mean (SD) maternal body weight was 74.0 (13.3) kg. Conclusion: On a weight-adjusted basis, the mean RID of rimegepant was <1% of the maternal dose.

Maternal and Child Symptoms Following COVID-19 Vaccination Among Breastfeeding Mothers.

Background: The impact of COVID-19 vaccination on breastfeeding is unknown. The primary aim of this study was to determine whether vaccine-related side effects following COVID-19 vaccination were associated with an adverse impact on breastfeeding. Secondarily, we sought to determine perceived symptoms in breastfed children and maternal opinion about COVID-19 vaccination. Materials and Methods: We conducted a cross-sectional survey of breastfeeding mothers who underwent COVID-19 vaccination >2 days before the survey. Subjects were recruited through social media and websites. Data included sociodemographic information, vaccine history, maternal and child symptoms, and impact on lactation/breastfeeding. Bivariate statistics (chi-square, Wilcoxon rank sum, and t tests) and multivariable logistic regression models examined the association of vaccine side effects with lactation, symptoms in breastfed children, and maternal opinion on vaccination. Results: Analysis included 4,455 breastfeeding mothers. Maternal postvaccination symptoms were more common after the second dose (p < 0.001). Overall, 77 (1.7%) respondents reported a negative impact on breastfeeding postvaccination, and these mothers were more likely to have experienced fatigue, headache, muscle pain, injection site pain, chills, fever, or allergic reactions. After adjusting for confounding variables, higher odds of an adverse impact on lactation were associated with lower breastfeeding intensity, dose of vaccine, and child symptoms. Even among mothers who reported an adverse impact on breastfeeding, maternal opinion about vaccination and confidence in their decision to receive the COVID-19 vaccine were high. Conclusions: COVID-19 vaccination among breastfeeding mothers resulted in minimal disruption of lactation or adverse impact on the breastfed child. These findings may be considered in vaccination decision-making.

Maternal Transfer of Cetirizine Into Human Milk.

INTRODUCTION: Cetirizine hydrochloride is a second-generation H1 histamine antagonist with Food and Drug Administration approval for treatment of allergic rhinitis and urticaria. Currently, the Food and Drug Administration does not recommend use of cetirizine during breastfeeding, as there are insufficient studies on both the transference of cetirizine into human milk and the effects of cetirizine in infants. MAIN ISSUE: To determine the concentration of cetirizine in human milk, samples were analyzed using high performance liquid chromatography mass spectrometry. MANAGEMENT: Based on calculations, relative infant dose was found to be 1.77% at 24 hr. In addition, there were no reported adverse effects seen in the infants. CONCLUSION: We suggest that transfer of cetirizine into human milk is minimal and unlikely to pose a significant risk to the breastfeeding infant. This is the first report presenting the transfer of cetirizine in human milk.

Transfer of the Serotonin Modulator Vortioxetine into Human Milk: A Case Series.

Background: Vortioxetine (Trintellix) is a serotonin modulator used in the treatment of major depressive disorder in adults. There are no data presently published on the transfer of vortioxetine into human breast milk. Case Report: The present study determined the drug concentration-time profile of vortioxetine in milk samples collected from three lactating mothers, two consuming 10 mg once daily and one consuming 20 mg once daily. Milk levels were measured using liquid chromatography mass spectrometry. At a dose of 10 mg/day, the maximum concentration of vortioxetine in milk was 13.89 ng/mL. At a dose of 20 mg/day, the maximum concentration in milk was 52.32 ng/mL. The relative infant dose was calculated to be 1.1% for 10 mg dose and 1.7% for 20 mg dose. Conclusion: In these three cases, we found the levels of vortioxetine in breast milk to be low and dose proportional. However, both RID's for 10 and 20 mg doses (1.1% and 1.7%, respectively) fall below the 10% theoretical level of concern and no adverse effects were reported by the mothers. As this is a small patient sample, caution should be exercised until further studies report the safety profile of vortioxetine in breastfeeding infants.

Human Milk Endocannabinoid Levels as a Function of Obesity and Diurnal Rhythm.

The endocannabinoid system is involved in the regulation of a variety of physiological and cognitive processes. While the endocannabinoids 2-arachidonoylglycerol (2-AG) and anandamide (N-arachidonoylethanolamine, AEA) have been found in breast milk, their role(s) have yet to be determined. This study determined the normal concentration ranges of endocannabinoids (2-AG and AEA) in breast milk and the influences, if any, of obesity and diurnal rhythms on their levels. Milk samples were collected from 36 breastfeeding mothers at 4-8 weeks postpartum at each feed over a 24-h period, and further stratified into three groups based on body mass index (BMI). The samples were analyzed using liquid chromatography mass spectrometry. AEA was below the limit of detection and 2-AG levels averaged 59.3 ± 18.3 ng/mL (± SD) in women with normal BMI. Wide-ranging 2-AG concentrations in the overweight (65.5 ± 41.9 ng/mL) /obese (66.1 ± 40.6 ng/mL) groups suggest BMI may be a contributing factor influencing its levels. Following a diurnal pattern, there was a significantly higher 2-AG concentration observed during the day, as compared to night time samples. In conclusion, our study clearly suggests that appropriate milk collection and storage conditions are critical. Further, body weight and diurnal rhythm appear to influence levels of 2-AG. Based on these results, future studies are underway to determine what specific roles endocannabinoids may play in human milk and how elevated levels of 2-AG may modulate infant appetite and health.

Dexmedetomidine Levels in Breast Milk: Analysis of Breast Milk Expressed During and After Awake Craniotomy.

Background: Dexmedetomidine is an α2-adrenoreceptor agonist with utility in sedation and analgesia for the perioperative or intensive care patient. The literature regarding the safety of dexmedetomidine in lactating patients is very limited. Methods: We present a case of a lactating patient who received dexmedetomidine bolus and infusion as part of her intraoperative sedation during an awake craniotomy. Breast milk samples were expressed by the patient twice intraoperatively and twice postoperatively. All samples collected were analyzed using liquid chromatography mass spectrometry. Results: Dexmedetomidine concentrations in the breast milk were measured at various intervals and were 88 and 50 pg/mL intraoperatively, and 89 and 15 pg/mL postoperatively. Conclusion: Levels of dexmedetomidine in breast milk were exceedingly low. Interruption of breastfeeding and/or discarding expressed breast milk may not be necessary after dexmedetomidine in breastfeeding mothers. Further investigation with a larger sample size is warranted to describe safety profile of dexmedetomidine in breastfeeding infants.

Rivaroxaban Treatment in Two Breastfeeding Mothers: A Case Series.

Background: Rivaroxaban (Xarelto) is a reversible direct factor Xa inhibitor used for the treatment and prevention of coagulation in numerous syndromes. There is very limited information available on the transfer of rivaroxaban into human breast milk. Case Report: This study determined the drug concentration-time profile of rivaroxaban in milk samples collected from two lactating mothers consuming 15 mg twice daily. After 21 days, each mother transitioned to 20 mg once daily. Levels in milk were measured using liquid chromatography mass spectrometry and analysis was done for both dosages. The maximum concentration of rivaroxaban observed for the 15 mg dose was 0.3 ± 0.02 µg/mL and that for the 20 mg dose was 0.26 ± 0.01 µg/mL. The relative infant dose (RID) was calculated to be 5% and 4%, respectively. Discussion: This relatively low infant dose is probably explained by the high plasma protein binding of rivaroxaban and its subsequent poor penetration into human milk. The results indicate that rivaroxaban receded to minimum concentration over a period of 12 hours. Conclusions: In these two cases, we found the levels of rivaroxaban in milk to be quite low, and the RID to be 5% of the maternal dose. Although the levels detected were low, rivaroxaban does transfer into breast milk. Caution should be exercised until further studies are conducted and report the safety profile of rivaroxaban in breastfeeding infants.

Transfer of Dicloxacillin into Human Milk.

Background: Dicloxacillin is a beta-lactam antibiotic that is commonly used in the treatment of lactational mastitis in breastfeeding women. Although penicillins have long been considered safe for breastfeeding mothers and their infants, there is almost no data on the transfer of dicloxacillin into human breast milk despite the fact that it is commonly used for mastitis. Case Report: This study determined the drug concentration-time profile of dicloxacillin in milk samples collected from three lactating mothers consuming 500 mg dicloxacillin taken every 6 hours for treatment of mastitis. Milk levels were measured using liquid chromatography mass spectrometry. The maximum concentration of dicloxacillin in milk was 67.6 ng/mL. The relative infant dose (RID) was calculated to be 0.03%. This value is well below the theoretical level of concern of 10%. Discussion: The limited transfer of dicloxacillin into human milk is probably explained by the high plasma protein binding of dicloxacillin and its subsequent poor penetration into human milk. Conclusion: In this case series, the level of dicloxacillin in milk was found to be very low, and the RID to be only 0.03% of the maternal dose. Although the levels detected were low, dicloxacillin does transfer into breast milk. Caution should be exercised in infants with hypersensitivity to penicillins.

Dimethyl fumarate transfer into human milk.

Dimethyl fumarate (DMF) is approved for the treatment of relapsing-remitting multiple sclerosis. It is unknown whether DMF or its primary metabolite monomethyl fumarate (MMF) are excreted into human milk. We present two cases of lactating patients who donated milk samples to study the transfer of MMF into human milk following a week of 2 × 240 mg daily oral dose. Samples were analyzed using liquid chromatography mass spectrometry. The calculated relative infant dose was 0.019% and 0.007%. This is the first study to demonstrate that MMF is transferred into human milk, with only limited exposure to an infant.