Figure 3. Idealized output of drug release systems.

(A) Systemic bolus of intravenous chemotherapy results in a quick spike of the tumor drug concentration followed by short duration of therapeutic drug concentrations in the tumor. The therapeutic index is much narrower between (A) systemic chemotherapy and (B & C) local therapy. (B) Local implants with slow sustained drug release can maintain a therapeutic drug dose, however the long ramp up time to reach therapeutic doses may increase drug resistance. (C) Ideally, an implant has quick-burst drug release to quickly reach therapeutic drug levels followed by sustained delivery of drug to maintain therapeutic dosage (solid line). Implants that burst release too much of their loading drug dose will be unable to maintain tumor drug levels at a therapeutic dosage (dashed line).