How to interpret the information
Medication levels in breastmilk are affected by several properties, such as the medication’s molecular weight, protein binding, pKa, and volume of distribution. A few commonly used terms in lactation literature for medications include the relative infant dose (RID) and milk/plasma (M/P) ratio.
RID provides information about relative medication exposure for the infant. It is calculated by dividing the infant’s dose of a medication via breastmilk (mg/kg/d) by the mother’s dose (mg/kg/d).7 Most consider an RID <10% to be safe.7
M/P is the ratio of medication concentration in the mother’s milk divided by the medication concentration in the mother’s plasma. A ratio <1 is preferable and generally indicates that a low level of medication has been transferred to human milk.7
Another factor that can be evaluated is protein binding. Medications that are highly protein-bound do not tend to pass as easily into breastmilk and can minimize infant exposure.
Several risk categorization systems are available, depending upon the resource used to obtain lactation information. One common system is Hale’s Lactation Risk Categories, with 5 safety levels ranging from L1 (breastfeeding compatible) to L5 (hazardous) (Table 17). Briggs et al8 utilize 7 categories to summarize recommendations ranging from breastfeeding-compatible to contraindicated; however, it is important to read the full medication monograph in the context of the rating provided. Table 27,8 provides breastfeeding information from Hale’s7 and from Briggs et al8 for some commonly used antidepressants.
In addition to interpreting available literature, it is also important to consider patient-specific factors, including (but not limited to) the severity of the patient’s psychiatric disorder and their previous response to medication. If a mother achieved remission on a particular antidepressant in the past, it may be preferable to restart that agent rather than trial a new medication.
CASE CONTINUED
Two weeks later and following the use of a variety of resources, Ms. D’s treatment team finds that mirtazapine is rated Probably Compatible (L3 in Hale’s Lactation Risk Categories), with an M/P ratio of 0.76.7 The RID of mirtazapine ranges from 1.6% to 6.3%, and limited data from infants exposed to maternal use of mirtazapine during breastfeeding have not shown adverse effects.5 The treatment team administers the EDPS to Ms. D again and she scores 18. Given Ms. D’s previous remission with mirtazapine, current severity of depressive symptoms, and the risk/benefit assessment from lactation resources, the decision is made to restart mirtazapine 15 mg/d at bedtime with the option to titrate up if indicated. Ms. D plans to continue breastfeeding and will monitor for signs of any adverse effects in her infant. The Figure provides a summary of navigating this individualized decision with patients.
Related Resources
- MotherToBaby. Medication fact sheets, option to contact for no-charge consultation, free patient education information materials. www.mothertobaby.org
- Reprotox. Summaries on effects of medications on pregnancy, reproduction, and development (subscription required). www.reprotox.org
Drug Brand Names
Bupropion • Wellbutrin
Citalopram • Celexa
Duloxetine • Cymbalta
Escitalopram • Lexapro
Fluoxetine • Prozac
Mirtazapine • Remeron
Nortriptyline • Pamelor
Paroxetine • Paxil
Sertraline • Zoloft
Trazodone • Oleptro
Venlafaxine • Effexor
Vortioxetine • Trintellix