Therapeutic Availability TA

Hunt et al. [6] introduced the term Therapeutic Availability as the ratio of the fraction of the dose reaching the target sites, if the dose is administered as the drug-carrier conjugate, to the fraction of the dose which reaches the same sites if an equal dose of the active drug is administered intravenously, as formulated below. 

Boddy et al. [7] defined the Therapeutic Availability as the ratio of the rate of input of free drug divided by that of the drug carrier for the same degree of maximal therapeutic effect. When considering steady-state conditions, this definition is equivalent to that shown in Eq. 13.20 and 13.21. 

Hunt et al. [6] also introduced the Drug Targeting Index, which was defined as the ratio of drug delivered to the target and toxicity sites when the drug-carrier conjugate is administered, divided by the same ratio when the active drug is administered intravenously and is formulated as follows. 

Hunt et al. [6] demonstrated that the DTI is also equivalent to the ratio of the therapeutic index (abbreviated to TI in Hunt et al. s paper in this chapter TI is defined differently, see Section 13.4.3) of the drug-carrier conjugate and that of the free drug. The therapeutic index (also called the therapeutic ratio) is a statistical measure defined as the ratio of the median toxic dose to the median effective dose [22]. 

Hunt et al. [6] considered the DTI the best measure of the effectiveness of the carrier. 

---