Oie-Tozer equation

The distribution of a drug in the body is largely driven by its physicochemical properties and in part for some compounds by the contribution of transporter proteins [17]. By using the Oie-Tozer equation and estimates for ionization (pfCj). plasma protein binding (PPB) and lipophilicity (log quite robust predictions for the volume of distribution at steady state (Vdss), often within 2-fold of the observed value, can be made [18]. 

The//(tissue) values are averaged for the species, this average is assumed to be the value for human, inserted back into the Oie-Tozer equation and combined with the measured value of /,(piasma) in human to obtain a predicted value for human VD. However, despite its increased complexity it does not offer additional accuracy over the above mentioned dog-human proportionality method and may only be most appropriate when plasma protein binding shows considerable inter-species variability. 

Some physiological volumes are known or have been estimated. Over two decades ago, Oie and Tozer proposed a relationship between the volume of distribution of a drug and its extent of plasma and tissue binding, using various fixed values for plasma and extracellular fluid volumes [1], This equation has been utilized in some methods used for prediction of steady-state VD, which will be discussed later ... 

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