Reduction in absorption of gallium maltolate in adult horses following oral administration with food: chemistry and pharmacokinetics.

Gallium (Ga) is under study for the treatment of osteolytic disorders in equines. Previous studies indicate that oral gallium maltolate (GaM) would provide a higher bioavailability than oral Ga salts. However, oral administration to adult horses of 2 mg/kg of GaM, in the form of a solution mixed with food, did not lead to detectable Ga levels in plasma. Therefore, a study was performed to model the chemical behaviour of GaM in the digestive tract. The equilibrium formation constants for Ga(III) and maltol were calculated by means of UV­visible measurements and validated by 1H-NMR measurements at selected pH values. Data indicate that the dissociation of GaM in aqueous solutions is very rapid, while the re-association is slower. Based on these results, poor Ga absorption seems to be due to the equilibrium dissociation of GaM in the stomach and to its slow formation rate in the intestine. The concomitant presence of high concentrations of phytates (strong charged metal chelating agents, which represent about 1% of dry matter in vegetables) might also explain the low absorption of GaM by the gastrointestinal tract. Methods of optimizing Ga absorption after oral administration of GaM require further investigation.

Pharmacokinetics of gallium nitrate after oral administration in adult horses--pilot study.

Gallium (Ga), a metal in group IIIA of the periodic table, has shown a remarkable activity against bone resorption and could therefore possibly prove useful in the treatment of certain diseases in sport horses, for example navicular disease. The aim of this study was to gain more information concerning the kinetics of Ga after oral administration of gallium nitrate (GaN) in adult horses. Six horses received a single dose of 10 mg/kg of GaN mixed with the food ration. Absorption was slow (T(max) = 10 ± 3 h, T(½abs) = 2 ± 0.8 h), and a C(max) of 26 ± 11 µg/L was achieved. Excretion followed a one-phase elimination model, with a long half-life (T(½el) = 52 ± 14 h). By means of a mathematical model, we estimated that the plasmatic levels should reach 93 µg/L (1.33 µm) at steady state, following the repeated daily administration of 10 mg/kg of GaN. A three times lower concentration has been demonstrated as effective in inhibiting the osteolytic activity of osteoclasts in vitro. The results of this study suggest that the administration of oral GaN at a rate of 10 mg/kg per day may be considered for future clinical studies.