Measuring a drug in milk can establish a route of potential infant exposure without reconstructing the amount taken by the mother. A two-person 2009 study of intravenous methamphetamine use demonstrates that distinction particularly clearly: the milk concentrations were measured, but the source material’s amount and purity were unknown.
What did the investigators actually observe?
Bartu, Dusci and Ilett opportunistically studied two breastfeeding mothers following self-reported intravenous use. They did not administer the drug. Urine was collected about four hours afterward; milk was collected before use and at two- to six-hour intervals for 24 hours. GC–MS identified urine analytes, and HPLC quantified milk analytes. Breastfeeding was withheld during the collection period. Bartu et al., 2009.
Average first-day milk concentrations were methamphetamine 111 and 281 µg/L, with amphetamine 4 and 15 µg/L, respectively. Estimated combined infant doses were approximately 17.5 and 44.7 µg/kg/day, expressed as methamphetamine equivalents. These were calculated potential milk-borne doses, not observed infant ingestion or infant plasma measurements. The paper used “methylamphetamine,” an alternative name for methamphetamine. Original methods and results.
Why cannot those measurements recover a maternal dose?
The unknown input and the observed milk output are different parts of a pharmacokinetic problem. Working backward requires information about distribution, elimination, sampling and individual variability. Two concentration profiles cannot establish a general conversion factor from a milk concentration to an injected amount.
A street-unit description is also not an analytical mass. Even if the user accurately describes the material obtained, its drug content remains uncertain unless the material is measured. A numerical dose inferred from that description would add precision unsupported by the study.
Why keep methamphetamine and amphetamine separate?
The laboratory measured two compounds. Combining their estimated doses requires an explicitly defined conversion, which is why the paper labels the sum as methamphetamine equivalents. That convention does not make the raw concentrations interchangeable. Nor does detecting both compounds, by itself, prove that two separate drugs were administered.
A potential infant dose in µg/kg/day is also different from a milk concentration in µg/L. Converting between them requires an intake assumption. If a report omits milk volume or uses a different intake model, the resulting dose should not be presented as a direct laboratory finding.
Can this study define a universal waiting period?
A 24-hour collection window is an observation period, not proof that drug disappears when that period ends. A historical recommendation derived from a tiny pharmacokinetic series is also different from a current, broadly validated clinical protocol. This article does not turn the study’s timing into individualized feeding advice.
For retrospective interpretation, the defensible approach is to separate measured milk concentration, modeled potential intake and documented feeding. Those three records may point in the same direction, but they are not substitutes for one another. Without infant specimens or independently documented ingestion, the study cannot establish a particular infant’s absorbed dose, clinical effect or cause of an adverse event.
Source
Bartu A, Dusci LJ, Ilett KF. Transfer of methylamphetamine and amphetamine into breast milk following recreational use of methylamphetamine. British Journal of Clinical Pharmacology. 2009;67:455–459. doi:10.1111/j.1365-2125.2009.03366.x. Two-person observational pharmacokinetic study; historical evidence.