Dr. Hale's Lactation Risk Categories

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 Probably 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 Potentially Hazardous

There is positive evidence of risk to a breastfed infant or to breastmilk 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.

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% to 10%. Side effects vary from one patient to another, with most patients not experiencing untoward effects.

Pediatric Concerns

This section lists the side effects noted in the published literature as associated with medications transferred via human milk. Pediatric concerns are those effects that were noted by investigators as being associated with drug transfer via milk. In some sections, I have added comments that may not have been reported in the literature, but are well-known attributes of this medication.

Infant Monitoring

This section provides advice to the clinician regarding potential side effects that may occur in the infant from exposure to a medication in breastmilk. The infant monitoring parameters can be used by the clinician to educate the mother about potential side effects that could occur in the infant.

Relative Infant Dose

The Relative Infant Dose (RID) is calculated by dividing the infant’s dose via milk in “mg/kg/day” by the maternal dose in “mg/kg/day” (see page xi). This weight-normalizing method indicates approximately how much of the “maternal dose” the infant is receiving. Many authors now use this calculation because it gives a better indication of the relative dose transferred to the infant. I report RID ranges, as this gives the reader an estimate of all the RIDs published by the various authors.

Please understand, however, that many authors use different methods for calculating RID. Some are not weight-normalized. In these cases, their estimates may differ slightly from this book. While I often place these authors’ estimates of RID in the text, the RID range that I calculate is weight-normalized in all instances when the maternal weight is provided. So RID may be slightly different according to how it is calculated.

Many researchers now suggest that anything less than 10% of the maternal dose is probably safe. This is usually correct. However, some drugs (metronidazole, acetaminophen) actually have much higher RIDs, but because they are quite non-toxic, they do not often bother an infant. To calculate this dose, I chose the data I felt were best, and these often included larger studies with AUC calculations of mean concentrations in milk. When maternal weights are not published, I choose an average body weight of 70 kg for an adult. Thus, most of the RIDs herein are calculated assuming a maternal average weight of 70 kg and a daily milk intake of 150 mL/kg/day in the infant.