Prediction of drug concentrations in human skim milk from plasma protein binding and acid-base characteristics.

1. Protein binding in human skim milk of a series of seven drugs with diverse plasma protein binding and acid-base characteristics, was measured by ultrafiltration. 2. A mathematical relationship between plasma and skim milk unbound fractions was established using measured values from this study along with values from the literature. 3. The relationship enables prediction of unknown protein binding values of drugs in skim milk from known plasma protein binding values. 4. Knowledge of milk protein binding enables a more accurate assessment of total milk concentrations than is available from existing theory which is limited to prediction of unbound drug.