Methods for covalently immobilizing glucose oxidase in polypyrrole are investigated. The enzyme was chemically modified with pyrrole using one of three different reactive side chains found in the protein. The reactions involve carbodiimide coupling to either lysyl or carboxyl residues on the enzyme and Schiff base reaction of the carbohydrate moiety. O ptimal coupling was achieved with the carbodiimide reaction, 15-20 mol of pyrrole/mol of enzyme compared with 6 mol of pyrrole/mol of enzyme for the Schiff base method. The pyrrole-substituted enzymes were electrochemically active, showing that the pyrrole moieties were oxidizable. Electropolymerized enzyme films deposited from solutions of free pyrrole and amounts of native or pyrrole-modified enzyme of equivalent activity resulted in covalently immobilized enzymes showing both higher enzyme activities and amperometric glucose responses than polypyrrole-entrapped native enzyme. The apparent Michaelis constant (Km* 1) and pH optimum of the modified enzymes electrodes correlated with that of the native enzyme electrode. Enzyme films generated from carbodiimide-modified enzymes were 6-fold more stable to thermal denaturation than native enzyme electrode.

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An excretion balance and pharmacokinetic study was conducted in cancer patients with solid tumors who received a single oral dose of capecitabine of 2000 mg including 50 microCi of 14C-radiolabelled capecitabine. Blood, urine and fecal samples were collected until radioactive counts had fallen to below 50 dpm/mL in urine, and levels of intact drug and its metabolites were measured in plasma and urine by LC/MS-MS (mass spectrometry) and 19F-NMR (nuclear magnetic resonance) respectively. Based on the results of the 6 eligible patients enrolled, the dose was almost completely recovered in the urine (mean 95.5%, range 86-104% based on radioactivity measurements) over a period of 7 days after drug administration. Of this, 84% (range 71-95) was recovered in the first 12 hours. Over this time period, 2.64% (0.69-7.0) was collected in the feces. Over a collection period of 24-48 h, a total of 84.2% (range 80-95) was recovered in the urine as the sum of the parent drug and measured metabolites (5'-DFCR, 5'-DFUR, 5-FU, FUH2, FUPA, FBAL). Based on the radioactivity measurements of drug-related material, absorption is rapid (tmax 0.25-1.5 hours) followed by a rapid biphasic decline. The parent drug is rapidly converted to 5-FU, which is present in low levels due to the rapid metabolism to FBAL, which has the longest half-life. There is a good correlation between the levels of radioactivity in the plasma and the levels of intact drug and the metabolites, suggesting that these represent the most abundant metabolites of capecitabine. The absorption of capecitabine is rapid and almost complete. The excretion of the intact drug and its metabolites is rapid and almost exclusively in the urine.