Comment: Prediction of Milk/Plasma Concentration Ratio of Drugs

Drugs in Lactation

One impediment to breastfeeding is the lack of information on the use of many drugs during lactation, especially newer ones. The principles of drug passage into breastmilk are well established, but have often not been optimally applied prospectively. Commonly used preclinical rodent models for determining drug excretion into milk are very unreliable because of marked differences in milk composition and transporters compared to those of humans. Measurement of drug concentrations in humans remains the gold standard, but computer modeling is promising. New FDA labeling requirements present an opportunity to apply modeling to preclinical drug development in place of conventional animal testing for drug excretion into breastmilk, which should improve the use of medications in nursing mothers.

Modeling drug passage into human milk

Breastfeeding has positive health consequences for both the breastfed infant and the nursing mother.(1,2) Although information on drug use during lactation is available through sites such as LactMed,(3) available information is often incomplete. Unlike pregnancy, in which large numbers of pregnant women need to be studied to assure safety, measurement of drug concentrations in breastmilk in a relatively few subjects can provide valuable information to assess drug safety. This article reviews methods of measuring and predicting drug passage into breastmilk.

Individualized drug and dose: The clinical pharmacologist's calling or curse?

1. The role of the clinical pharmacologist is to promote the rational, safe and effective use of medicines. This revolves around the notion of variability, between and within patients and between and within drugs, in terms of both pharmacokinetics and pharmacodynamics. Ideal therapeutics involves tailoring the drug and its dosing to the individual patient, taking into account this variability. 2. In the 25 years of my membership of the Australasian Society of Clinical and Experimental Pharmacologists and Toxicologists, three themes have dominated my research: (i) drugs and breast feeding; (ii) aminoglycoside dosing; and (iii) pharmacogenetics. In all these, the research has been orientated towards identifying factors involved in variability and working towards dose individualization based on the understanding of these factors. 3. Our model for predicting drug concentrations in milk has assisted not only in estimating the safety of drug ingestion via breast milk, but also in the understanding of the processes involved in drug transfer. 4. The aminoglycoside studies have assisted in the understanding of the basis behind extended interval dosing, leading to a model for dose prediction that is widely used, especially in Australasia. 5. Pharmacogenetics is a field widely acclaimed as having a huge future in terms of individualization of drug therapy. Our early studies in this area lend only cautious support to this optimism.