The ongoing patent battle relating to Cefdinir polymorphism and crystalline forms is described from a scientific point of view. This case study illustrates some of the strategies adopted by generic bulk manufacturers to challenge originator's patents on polymorphic forms.

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Cytotoxicity, morphological neoplastic transformation, cellular uptake and metabolic reduction were determined in BALB/3T3 Cl A31-1-1 cells for trivalent arsenic (sodium arsenite, As3+) and for pentavalent arsenic (sodium arsenate, As5+). The levels of cellular uptake of 73As-labelled sodium arsenite and arsenate were dose-dependent and highest in the first hour. At equimolar concentration (3 X 10(-6) M), cellular uptake was 4-fold higher for As3+ than for As5+. Cytotoxicity was higher for As3+ than for As5+, but when correlated to total As cell burden it showed no significant difference for the two forms. Morphological transformation focus assays showed transforming activity for both As3+ and As5+, with relative transformation frequencies also of approximately 4:1. Recovery from the cytosol after exposure for 1-24 h was greater than 90% for either form of absorbed As. Exposure to As3+ yielded 100% as As3+ in cytosol, but exposure to As5+ yielded greater than 70% as As3+, showing a high rate of intracellular metabolic reduction. No methylated metabolites were detected by ion-exchange chromatography. After 24-h incubation in cell-free medium, oxidation of As3+ to As5+ occurred up to 30% of the dose, but incubation in the presence of cells lowered the oxidation level to 4%. As5+ was recovered unchanged from cell-free medium (24-h incubation), but in the presence of the cells it yielded up to 5% as As3+ within 24 h and the cumulative release of As3+ by cells exposed to As5+ was dose-dependent. Glutathione depletion by diethylmaleate inhibited reduction of As5+ to As3+ by these cells up to 25% of controls, showing that As5+ reduction is partly dependent on glutathione. These results suggest that As3+ is the form responsible for the cytotoxic and transforming effects, independently of the valence state of the inorganic arsenic in the culture medium.

Cytotoxicity and morphological transformation has been studied in BALB/3T3 Cl A31-1-1 mouse embryo cells for ammonium vanadate [vanadium(V)] and vanadyl sulphate [vanadium(IV)] alone or in combination with diethylmaleate (DEM), a cellular glutathione (GSH)-depleting agent. Cells exposed for 24 h to 10(-5) M vanadium(V) alone or in combination with 3 x 10(-6) M DEM showed the characteristic hyperfine EPR signal of vanadium(IV), which was more obvious in the case of exposure to vanadium(V) alone. This suggests that the amount of vanadium(V) reduced to vanadium(IV) decreased in GSH-depleted cells. While vanadium(IV) at concentrations of 3 x 10(-6) M and 10(-5) M was not transforming in the cells, vanadium(V) showed neoplastic transforming activity (P < 0.025 and P < 0.001 for the two doses, respectively) in comparison to controls (vanadium unexposed cells). Cytotoxicity and morphological transformation in cells exposed to vanadium(V) in combination with 3 x 10(-6) M DEM were significantly more intensive (P < 0.005 and P < 0.01 for the two doses of vanadate tested) compared to the corresponding values observed in cells exposed to vanadium(V) alone. This suggests that the final transforming activity response is dependent on the intracellular GSH-mediated mechanism of reduction of vanadium(V) to vanadium(IV): (i) the extent to which vanadium(V) should be bioreduced to less toxic vanadium(IV) via intracellular GSH is a key point in determining the intensity of the observed neoplastic action; (ii) the carcinogenic potential of vanadium(V) should be strictly dependent on its intracellular persistence which could lead to changes in normal metabolic patterns of vanadium(V) in the oxidized form due to lack of GSH-mediated reduction.

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