Jill: I'm no pharmacologist, but I did attend a lecture by Cheston Berlin, one of the members of the AAP's Committee on Drugs in Human Milk, about 2-3 years ago at a LLL Physician's Seminar. He said that the concept of the drug being stored in the breast is incorrect. The production of milk is a very dynamic process, with reabsorption and diffusion back into the bloodstream. Although a small amount of milk is stored over time, the bulk of the milk produced is being made at the time the baby nurses, therefore it is the concentration in the milk at that time that counts. It's important to keep in mind that there is a big difference between drugs used acutely for a few days, which peak after a dose and drop to fairly low concentrations at the end of a dosing interval (known as the trough), compared with chronic medications, which after the initial several half-lives reach what's known as steady-state concentration. This means that although the concentration of the drug in the mother's bloodstream goes up a little with each dose and drops slightly at the trough, the drug has a significant steady concentration in the mother's blood. This would be a situation where the timing of the dose probably wouldn't make much difference. I don't have a reference, but I can try to get one if you need. Alicia. [log in to unmask]