The effect of sulphamethoxypyridazine on liver and plasma levels of vitamin A in rats.

1 Long-acting sulphonamides are highly bound to plasma proteins; the present study deals with the effects of this binding property upon a vitamin A compound also transported by plasma proteins. 2 Sulphamethoxypyridazine was administered in rats either orally or by intraperitoneal injection. 3 A significant fall in plasma vitamin A level and an increase in hepatic vitamin A concentration were observed. 4 These results suggest an interference by sulphamethoxypyridazine with the transport of vitamin A, either through competition between the drug and vitamin A for binding sites of plasma proteins, or through altered secretion of the vitamin from the liver.