Local disposition kinetics of floxuridine after intratumoral and subcutaneous injection as monitored by [19F]-nuclear magnetic resonance spectroscopy in vivo.

PURPOSE

To test the utility of [19F]-nuclear magnetic resonance (NMR) spectroscopy for studying the kinetics of local drug disposition after interstitial application in vivo.

METHODS

Floxuridine at 30 micromol (2.5% of the reported i.p. 50% lethal dose, LD50) was injected into rats either intratumorally (Morris hepatoma M3924A) or s.c. [19F]-NMR spectra were obtained at the site of administration for up to 5 h after injection using a 2-cm diameter surface coil at 2.0 T. Signal-time data obtained for floxuridine and the metabolite 5-fluorouracil were analyzed using linear compartment models.

RESULTS

The lower limit for the quantitation of drug remaining at the site of administration was 1 micromol for tumors and 0.2 micromol for the s.c. injection site. Local drug disposition was biexponential in four of six tumors where the half-lives of the fast and slow components of disposition ranged from 4 to 26 and from 33 to 289 min, respectively. It was monoexponential in the remaining two tumors (half-lives 49 and 128 min) and in the s.c. injection experiments (n = 4, half-life 6-9 min). 5-Fluorouracil could be quantitated in three of six tumors; the estimated fraction of floxuridine converted intratumorally into 5-fluorouracil was 11-23%. Alpha-fluoro-beta-alanine was detected in the sum spectra of three of the six tumours.

CONCLUSIONS

Local drug-disposition kinetics after interstitial application can be monitored noninvasively by in vivo [19F]-NMR spectroscopy. Disposition kinetics after local injection is highly variable and has a slow component in this tumor, whereas it is much less variable and relatively fast in subcutaneous tissue. The results suggest that NMR spectroscopy may be useful for in vivo studies of drug release from depot preparations designed for interstitial application.