Pharmacokinetic and pharmacodynamic aspects of site-specific drug delivery

Experimental determination of a drug targeting index for S(+)ibuprofen using the rat air pouch model of inflammation

We have used the rat air pouch model of inflammation and S(+)ibuprofen as an experimental model system to enable the quantitative assessment of the pharmacokinetic determinants of site specific drug delivery. S(+)ibuprofen (50 & 1mg/kg) was administered directly into six day old air pouches immediately following the injection of the irritant carrageenan. Serial exudate and plasma samples were collected and analysed for ibuprofen by HPLC. The procedure was repeated following administration of S(+)ibuprofen (20 & 5mg/kg) intravenously. The parameters describing events in the air pouch and plasma indicated linear kinetics over the doses employed. The dose normalised AUCs were then used to formulate a quantitative measure of benefit for S(+)ibuprofen delivered directly to the air pouch. A Drug Targeting Index (DTI) was calculated from the ratio of AUC in the air pouch and plasma following direct intrapouch administration divided by the same ratio following intravenous administration and gave a value of 130. This pharmacokinetic measure of benefit represents the maximum advantage afforded by the site specific delivery of S(+)ibuprofen as the whole of the administered dose is delivered directly to the site of action.

Increased tumor cisplatin levels in heated tumors in mice after administration of thermosensitive, large unilamellar vesicles encapsulating cisplatin

Hyperthermia (HT)-dependent cisplatin (CDDP) release and tumor CDDP level increase after the administration of thermosensitive, large unilamellar vesicles (LUVs: LUV-1 and LUV-2) and a thermosensitive, small unilamellar vesicle (SUV: SUV-1) were examined in comparison with those following administration of a non-thermosensitive LUV (LUV-3) and a CDDP solution (Sol) in tumor bearing mice. The LUV-1 and LUV-2 released CDDP at a faster rate than SUV-1 when incubated in saline at temperatures between 41 and 44 degrees C. The blood CDDP levels after liposome administration were higher than those after Sol administration. The systemic clearance of LUV-2 was slightly larger than those of the other liposomes. The tumor CDDP levels after thermosensitive liposome administration were increased in response to HT in comparison to LUV-3 or Sol. The increased ratio for LUV-1 was the largest. The ratio of the area under the tumor CDDP level versus time curve (AUC) for LUV-1 + HT to the AUC for Sol + HT was approximately 5. The results indicate that (1) the tumor-CDDP level increase after thermosensitive liposome administration is due to CDDP release from the liposome in the blood at or adjacent to the heated tumor, (2) the increase is highly dependent on the heat sensitivity and systemic stability of the liposome, and (3) LUV, such as LUV-1, exhibit higher heat sensitivity and larger, targeted drug delivery efficiency than SUV.

Application of a linear recirculation model to drug targeting

Current interest in drug targeting has inspired theoretical considerations of its potential and problems. Previously, drug targeting has been considered in terms of more or less elaborate compartmental models. The present paper shows how an equivalent analysis of the potential advantage of drug targeting may be derived with the minimum reliance on a specific model. A linear recirculation model is used to describe the drug concentration profile at some target site and in the rest of the body. Equations for the AUCs of drug and of a drug-carrier conjugate can then be derived. These AUCs are used to define a drug targeting index (DTI), a measure of drug targeting selectivity previously derived from a specific model. It is shown that the DTI can be defined solely in terms of extraction ratios for elimination of free drug, when release of drug is confined to the target site. The expression for DTI is shown to be equivalent to that previously derived from several more model-dependent approaches.