Dual-electrode amperometric detection for the determination of SR4233 and its metabolites with microbore liquid chromatography.

3-Amino-1,2,4-benzotriazine-2,4-di-N-oxide (SR4233) is a promising new antineoplastic agent based on reductive activation. SR4233 and its major metabolites (SR4317 and SR4330) are all easily reduced at a carbon electrode. Reductive amperometric detection can therefore provide high selectivity and low detection limits with chromatographic analysis and is an ideal approach to detection of SR4233 in microdialysis samples. However, in order to use amperometric detection in the reductive mode, sample deoxygenation is necessary. This is typically done by purging the sample with either argon or nitrogen prior to injection. This approach is not feasible for microdialysis samples because only 5-10 microliters is usually available. In this report, a microbore liquid chromatographic method with dual-electrode amperometric detection is described for the determination of SR4233 and its metabolites without predeoxygenation. A dual-electrode amperometric detector was used in the series configuration with an upstream potential of -450 mV to reduce SR4233 and its metabolites to a common product and a downstream potential of +400 mV to oxidize this product. Oxygen is only electroactive at the upstream electrode because of its irreversible behavior. This method is compatible with the small sample volumes provided by microdialysis sampling. Linear calibration graphs were obtained up to 55 microM for SR4233, and 140 microM for both SR4317 and SR4330. The detection limits were 70 nM for SR4233, and 50 nM for SR4317 and SR4330. The average intra-day variation over 5 days was 1.8% (SR4233), 1.4% (SR4330), and 1.8% (SR4317), whereas the inter-day variation over 5 days was 14.1% (SR4233), 8.6% (SR4317), and 2.6% (SR4330).

Microdialysis sampling in tumor and muscle: study of the disposition of 3-amino-1,2,4-benzotriazine-1,4-di-N-oxide (SR 4233).

Microdialysis sampling was used to study the pharmacokinetics and disposition of SR 4233 (3-amino-1,2,4-benzotriazine-1,4-di-N-oxide), a representative of a new class of bioreductive antineoplastic agents. The pharmacokinetics of unbound SR 4233 in plasma was determined using a flexible microdialysis probe implanted into the jugular vein of conscious, freely-moving rats. No difference in the plasma pharmacokinetics was observed between healthy and tumor bearing rats. In both cases a biexponential decay following an i.v. dose was observed with t1/2 (alpha) of 13.4 +/- 3.2 minutes and t1/2 (beta) of 37.0 +/- 14.4 minutes. Binding of SR 4233 to plasma proteins was determined to be concentration independent at 21.4 +/- 2.9%. A linear microdialysis probe was used to sample solid tumor and muscle tissue in vivo to study the disposition of SR 4233 into these tissues. Similar elimination kinetics were observed in both tissues although the peak concentration of SR 4233 in muscle was 20 times that in the tumor. The extent of reductive metabolism was much greater in the tumor relative to muscle. This was observed after both a systemic dose of SR 4233 and direct dosing to the tissue through the microdialysis probe. This study demonstrates the potential of microdialysis sampling in vivo to the study of the disposition of drugs.

Investigation of the degradation mechanism of 5-aminosalicylic acid in aqueous solution.

The solution degradation of the antiinflammatory agent 5-aminosalicylic acid (5-ASA) was investigated in order to elucidate a mechanism for degradation. Two degradation pathways were considered: decarboxylation by analogy to 4-aminosalicylic acid (4-ASA) decomposition and oxidation from consideration of 5-ASA's aromatic ring substitution pattern (i.e., relation to p-aminophenol). The oxidation of 5-ASA was investigated using cyclic voltammetry and flow electrolysis. These studies showed that 5-ASA is more easily oxidized than is 4-ASA and that 5-ASA undergoes a two-electron, two-proton oxidation consistent with formation of 5-ASA-quinoneimine (5-ASA-QI). This oxidation is followed by subsequent complex chemistry. The decomposition of 5-ASA in solution was examined under a variety of conditions. 5-ASA decomposes most rapidly under conditions promoting oxidation and is most stable under conditions tending to inhibit oxidation. Decarboxylation was not found to be a significant degradation pathway.