L1 - Compatible
Drug which has been taken by a large number of breastfeeding mothers without any observed increase in adverse effects in the infant. Controlled studies in breastfeeding women fail to demonstrate a risk to the infant and the possibility of harm to the breastfeeding infant is remote; or the product is not orally bioavailable in an infant.
L2 - Probably Compatible
Drug which has been studied in a limited number of breastfeeding women without an increase in adverse effects in the infant, and/or the evidence of a demonstrated risk which is likely to follow use of this medication in a breastfeeding woman is remote.
L3 - Presumed Compatible
There are no controlled studies in breastfeeding women; however, the risk of untoward effects to a breastfed infant is possible, or controlled studies show only minimal non-threatening adverse effects. Drugs should be given only if the potential benefit justifies the potential risk to the infant. (New medications that have absolutely no published data are automatically categorized in this category, regardless of how safe they may be.)
L4 - Possibly Hazardous
There is positive evidence of risk to a breastfed infant or to breast milk production, but the benefits from use in breastfeeding mothers may be acceptable despite the risk to the infant (e.g., if the drug is needed in a lifethreatening situation or for a serious disease for which safer drugs cannot be used or are ineffective.)
L5 - Hazardous
Studies in breastfeeding mothers have demonstrated that there is significant and documented risk to the infant based on human experience, or it is a medication that has a high risk of causing significant damage to an infant. The risk of using the drug in breastfeeding women clearly outweighs any possible benefit from breastfeeding. The drug is contraindicated in women who are breastfeeding an infant.
Drug Monograph:
The narrative text summarizes what is known about the drug's transfer into milk, concentrations measured, and clinical relevance. We report what the literature documents and note where data are lacking.
Relative Infant Dose:
The estimated percentage of the maternal weight-adjusted dose that the infant receives via milk. Calculated as: (infant dose via milk in mg/kg/day) / (maternal dose in mg/kg/day) x 100 unless otherwise noted. An RID below 10% is generally reassuring, but this must be interpreted in context of the drug's potency and the maternal dose being used. RID ranges reflect values reported across different studies. See previous detailed discussion of RID and its limitations.
In this book, RID is calculated assuming a 70-kg mother and infant milk intake of 150 mL/kg/day. I chose the data I felt was best, often including larger studies with AUC calculations of mean concentrations in milk. Please note that authors calculate RID differently - some are not weight-normalized, others report RID per feeding rather than daily average. Values in this book may vary slightly from other sources due to these differences in calculation method.
Kinetic Parameters:
For detailed information on the kinetic parameters, please refer to the relevant sections previously discussed in the Preface.
| Parameter | What It Tells You |
|---|---|
| T½ (Adult Half-life) | Time for plasma concentration to drop by half. Shorter half-lives allow timing feeds to reduce exposure. Long half-lives may result in infant accumulation. |
| M/P (Milk/Plasma Ratio) | Ratio of drug concentration in milk to plasma. Limited clinical utility. A high M/P with low plasma levels still means low milk levels. |
| Tmax | Time to peak plasma concentration after dosing. This is when milk levels will be highest. Avoid feeding at Tmax when possible. |
| PB (Protein Binding) | Percentage bound to plasma proteins. High PB (>80%) means little free drug available to transfer into milk. |
| Oral (Oral Bioavailability) | Percentage absorbed into systemic circulation after oral administration. Low oral bioavailability in the infant means less systemic exposure even if the drug is present in milk. |
| Vd (Volume of Distribution) | How widely the drug distributes in the body (L/kg). High Vd (>1-2 L/kg) means the drug disperses into tissues, keeping plasma levels low. |
| pKa | The pH at which the drug is half ionized. High pKa (>7.2) can lead to ion trapping in milk. |
| MW (Molecular Weight) | Size of the molecule in Daltons. Drugs >500 Da passively transfer poorly. |
Adult Concerns:
This section lists the most prevalent undesired or bothersome side effects listed for adults. As with most medications, the occurrence of these is often quite rare, generally less than 1%-10% of the time. Side effects vary from one patient to another and should not be overemphasized, since most patients do not experience untoward effects.
Adult Dosage:
This is the usual adult oral dose provided in the package insert. While these are highly variable, I chose the dose for the most common use of the medication.
Pediatric Concerns:
Adverse effects reported in breastfed infants in the published literature. "None reported" does not mean "no risk" - it may reflect limited data.
Infant Monitoring:
Potential side effects that may occur in the infant from exposure to a medication in breast milk. The infant monitoring parameters can be used by the clinician to educate the mother about potential side effects that could occur in the infant.
Alternatives Drugs:
Listed in this section may be suitable alternate choices for the medication listed above. In many instances, if the patient cannot take the medication or it is a poor choice due to high milk concentrations, these alternates may be suitable candidates. WARNING: The alternates listed are only suggestions and may not be at all proper for the syndrome in question. Only the clinician can make this judgment.