Pharmacokinetics is the science which describes quantitatively the uptake of drugs by the body, their transformation inside the body, their distribution, their effect upon the body's function, the metabolism of the drugs, and their elimination from the body. Both total amounts of the drugs taken and their ultimate concentrations in tissues and organs are considered by the pharmacokineticist.
Toxicokinetics is essentially the same term applied to metabolically active chemicals other than drugs.
This writeup is based on work I did for the science dictionary at http://biotech.icmb.utexas.edu/.