Pharmacokinetics of anticancer drugs used in breast cancer therapy are well established. This chapter reviews preclinical and clinical pharmacokinetics of the following drugs: cyclophosphamide, docetaxel, doxorubicin, 5-fluorouracil, methotrexate and tamoxifen. The absorption, distribution, metabolism and elimination of drugs are discussed in the context of breast cancer. The effect of age and menopause status on drug pharmacokinetics is evaluated. The important role of pharmacokinetic-pharmacodynamic modeling in understanding the phenomenon of chemo fog, memory deficit in breast cancer chemotherapy, is explored.